Full text of "Textbook of Oyster Biology and Culture in India"

See other formats

Textbook of

Digitized by the Internet Archive

in 2018

https://archive.org/details/textbookofoysterOOOOnara

Textbook of

Oyster Biology
and

Culture in India

. r**

Textbook of

Oyster Biology
and

Culture in India

K.A. NARASIMHAM

Formerly Principal Scientist and Head of Molluscan Fisheries Division,
Central Marine Fisheries Research Institute, Cochin, Kerala 682 018

and

V. KRIPA

Senior Scientist

Central Marine Fisheries Research Institute, Cochin, Kerala 682 018

ICAR

' &>; j

V Copy

Published by

Directorate of Information and Publications of Agriculture

Indian Council of Agricultural Research
New Delhi 110 012

PRINTED : JULY 2007

Project Director (DIP A) : Dr T.P. Trivedi

Incharge (English Editorial) : Dr R.P. Sharma

Editing : Reena Kandwal

Chief Production Officer :
Technical Officer (Production) :

V.K. Bharti
Punit Bhasin

Senior Artist : B.C. Mazumder

ISBN No. : 81-7164-070-2

Price : Rs 400

Published by Dr T.P. Trivedi, Project Director (DIPA), Indian Council of
Agricultural Research, Krishi Anusandhan Bhavan I, Pusa, New Delhi 110 012;
Lasertypeset at M/s Print-O-World, 2579, Mandir Lane, Shadipur, New Delhi
110 008, and printed at M/s Chandu Press, D-97, Shakarpur, Delhi 110 092.

Preface

OYSTERS, an important group among the bivalve molluscs are highly
esteemed as seafood in many temperate countries where consumption of
raw oysters is popular. Oyster is probably the most studied invertebrate and
marine aquaculture may have begun with oysters. Oyster farming has a long
history and it has been reported that the Chinese practiced oyster culture
before the Christian era while in Europe the Romans farmed oysters since the
beginning of the first century B.C. by adopting the simple method of relaying
the oyster seed in suitable grow out areas. In late 1 920s the Japanese developed
the ‘hanging culture’ and by 1950s made rapid strides by adopting the raft and
long line oyster culture in depths upto 30 m. The latter half of the 20th century
ushered in the spread of oyster culture to several parts of the world and there
is growing interest in tropical countries, which have the advantage of cheap
labour and producing market size oysters in a short period of 6-10 months
against about 2 years or more in temperate countries, depending upon the
method of culture and the species. The noted oyster biologist Dr.Gary Newkirk
stated that oysters are cultured in all the continents except in the Antarctica.
As per the FAO statistics, the world aquaculture production of molluscs in
2003 was 1,22,84,758 mt and among them the oysters accounted for 44,96,609
tonnes (36%). These figures highlight the importance of oysters in the global
perspective. China emerged as a world leader in oyster production with about
three-fourth production as its share.

In India, the first attempt to farm the oysters on scientific lines was made
in 1910 by the British Biologist Dr. James Hornell. Realizing the importance
of oyster culture, the Central Marine Fisheries Research Institute initiated a
Research Project on oyster culture at its Tuticorin Research Centre in late
1970s by collecting natural spat. A devoted band of scientists under the able
leadership of Shri K. Nagappan Nayar, followed by others, have successfully
developed the technology of seed collection from nature, farming systems
using racks for holding trays and oyster rens and also large scale hatchery
production of seed. During 1 993-95 several programmes were taken up by the
CMFRI to assess the suitability of various sites in several states for oyster
culture by using both hatchery and natural spat. These studies showed that
several places in the four southern states are suitable for oyster culture, and the
most important being the Ashtamudi lake in Kerala which emerged as a highly
suitable site both for spat collection and grow-out culture. In the mean time,
significant contributions on various aspects of oyster culture have come from

Oyster Biology and Culture in India

the College of Fisheries, Mangalore. After nearly two decades ol research and
development by the CMFRI, the first commercial oyster farm came up in 1 996
at Dalavapuram in the Ashtamudi lake. Since then, with active suppoit, in
imparting training, technology transfer and continuous interaction in the field
with the oyster farmers by the CMFRI scientists, coupled with the involvement
and participation of financial institutions, developmental agencies and others,
oyster culture is fast picking up in Kerala, with the current production being
750-800 t. The average annual production of oysters by the harvest of wild
stocks is 18,800 tonnes / year. A major constraint at this time is marketing,
since in India oyster consumption is traditionally limited to a few coastal
communities and oysters are practically unknown in the vast interior of the
country except for a few metropolitan cities. The technology for the preparation
of several products with oysters is readily available in the country. The
availability of indigenously developed and time tested packages of oyster
culture technology, a strong research base to optimise production, increased
awareness among the prospective farmers about the economic benefits of
oyster culture and the readiness of developmental and financial institutions to
provide credit, augurs well for the rapid development of oyster culture in the
country.

Dr. K.A. Narsimham, senior author rendered over 37 years of service in
the CMFRI and has over 70 scientific papers to his credit. During his long
association with this Institute, he made significant contributions on most
groups of molluscs of commercial importance in India. He functioned as the
Head of Molluscan Fisheries Division for over four years. He played a major
role, in association with his colleagues, in identifying various sites suitable for
oyster culture in India and in the transfer of oyster culture technology to the
farmers. As Principal Investigator of the bivalve hatchery project, in
collaboration with his colleagues, he achieved a major breakthrough in the
large-scale hatchery seed production of various clam species. He is a recipient
of Ind. Aqua 1993 award, in recognition of his outstanding contributions in
developing complete package of technology for clam culture.

Dr. (Mrs.) V. Kripa, Senior Scientist and co-author of the book is working
in the CMFRI for the last 20 years. She has worked on the clam, oyster, mussel
and cephalopod resources of the south-west coast of India. She took the Ph.D.
degree from Cochin University of Science and Technology for her thesis on
the rock oyster Saccostrea cucullata. She also received National award in
2001 for her article in Hindi on “Molluscan Mariculture” under the non-Hindi
speaking category. She is playing a significant role in the technology transfer
of oyster culture with particular emphasis on women empowerment in this
area.

This book, Oyster Biology and Culture in India contains 12 Chapters and
after a general introduction to oysters in Chapter 1, oyster resources, their

Oyster Biology and Culture in India

VII

distribution and ecology are dealt in Chapter 2. Biology, unwanted species,
fisheries, seed production, technology of farming, economics of oyster culture
and technology transfer are dealt in Chapters 3 to 9 respectively. Chapter 10
gives information on oyster culture practices in major oyster producing countries
in the world and Chapter 1 1 on recent developments in oyster culture in the
global perspective. In the concluding Chapter 12, the authors, after a critical
examination of the current status of oyster resources and culture in India,
underscore the strategies for developing oyster culture in the country. This
book, although mainly targeted to meet the requirements of university teachers,
researchers and students is also expected to cater to the needs of personnel
from fisheries / rural development agencies, financial institutions, NGOs and
entrepreneurs. I am confident that this book will stimulate further research and
development initiatives in oyster culture in India.

(Mohan Joseph Modayil)

Director

Central Marine Fisheries Research Institute

Cochin - 682018.

Acknowledgements

WE are thankful to the Indian Council of Agricultural Research, New
Delhi for according sanction and providing financial assistance to write
this book on OYSTER BIOLOGY AND CULTURE IN INDIA under
‘University Level Text Book Writing Scheme’. It gives us great pleasure to
place on record our thanks to Prof (Dr) Mohan Joseph Modayil, Director,
Central Marine Fisheries Research Institute, Cochin for providing us all the
facilities for successfully completing the work, encouragement, and for the
keen interest evinced during the course of the work. We consider it a great
privilege to place on record our deep sense of gratitude to Dr P Vedavyasa
Rao, former Principal Scientist, CMFRI, who has spent considerable time by
critically going through the manuscript, for several helpful discussions and
constructive comments which have vastly contributed towards improving the
quality of presentation of the material in various chapters. We are indebted to
Dr KK Appukuttan, Principal Scientist and former Head of Molluscan Fisheries
Division, CMFRI for providing us the facilities and support given in various
ways, and for suggesting valuable improvements in the manuscript.

Several of our colleagues working in the CMFRI have extended help in
various ways. We are thankful to Dr TS Velayudhan, Principal Scientist for
literature and photographs, Dr KS Mohamed, Head, MFD, for going through
the section on Probiotics, for suggestions, help rendered in taking photographs
and for literature, to Dr P Jayasankar, Senior Scientist for going through the
section on genetics and offering comments, to Dr VK Pillai, Dr CP Gopinathan,
Principal Scientists and Dr PK Krishna Kumar, Senior Scientist for providing
literature. We are also thankful to Dr P Muthiah, Principal Scientist for giving
latest information on oyster culture. One of us (KAN) expresses his thanks to
Dr H Mohamed Kasim and Dr (Mrs) S Sivakami, former Officers-in-Charge
and Dr R Narayanakumar, Scientist-in-Charge, Dr AK Unnithan, Senior
Scientist and the staff of the Kakinada Research Centre of CMFRI for facilities
and help provided in various ways. The help rendered by Shri P Radhakrishnan,
Shri Mathew Joseph, Shri PS Alloycious, Ms J Sharma and other staff of
Molluscan Fisheries Division, CMFRI at Cochin is also gratefully
acknowledged. We are thankful to Dr NGK Pillai, Principal Scientist and
Head of Pelagic Fisheries Division, CMFRI for help rendered in several ways.

We express our thanks to Dr I Karunasagar, Professor, College of Fisheries,
Mangalore for the help rendered in sending the latest literature on microalgal
toxins and for the services put in by Shri KCS Kondala Rayydu, Ms Seema
Shri BNP Raju and Fellows, for the assistance given at various times during

Oyster Biology and Culture in India

the course of the work. We also express our gratitude to the Senior Research
Fellows, Mr Ramalinga, Ms R Jugnu, Ms Ani Kumari, Ms Leena Ravi, Ms R
Sreejaya and Ms Anjana Mohan for the assistance given for literature collection
and final compilation of the manuscript.

December, 2006

Dr KA Narasimham
Dr (Ms) V Kripa

Contents

Preface

A cknowledgements

Introduction

Questions

Oyster Resources,

Distribution and Ecology

Taxonomy

Distribution of Oysters

Ecology of Oyster Beds

Oyster Reef

Questions

Biology

Anatomy

Food and Feeding Habits

Reproduction

Age and Growth

Condition Index

Biochemical Composition

Questions

Unwanted Species

Foulers

Borers

Predators

Control of Foulers, Borers and Predators

Parasites and Diseases

Questions

Fisheries

World Oyster Production

Oyster Production in India

Oyster Fishing Methods

Fishing Season and Species Composition

Size and Age Composition

Subsoil Shell Deposits

Management of Oyster Fishery

Questions

XII

Oyster Biology and Culture in India

6. Seed Production 91

Natural Spat Collection 91

Natural Spat Collection in India 92

Seed Production in the Hatchery 96

Hatchery Production of Oyster Seed in India 97

Dry weight (mg) per million cells 107

Transportation of Oyster Seed 1 10

Questions 112

7. Technology of Farming 1 1 3

Selection of Farm Site 1 1 3

Nursery Rearing of Spat 1 15

Grow out Culture 116

Purification of Oysters for Market 129

Utilisation 134

Questions 135

8. Economics of Oyster Culture 136

Economics of Rack and Ren Method of Culture 137

Economics of Rack and Ren method as practiced by farmers 140
General Considerations 141

Questions 141

9. Transfer of Technology 142

Training on Oyster Culture 1 42

Development of Oyster Culture in Kerala 143

Social Impact of Oyster Culture 144

Oyster Culture and Rural Development 146

Questions 147

10. Present Status of Oyster Culture in the World 148

China 148

United States of America 150

Japan 152

France 156

Philippines 159

Thailand 161

Questions 163

11. Recent Developments in Oyster Culture 164

Remote Setting 170

Nursery Rearing of Spat 172

Probiotics 173

Genetics 174

Oysters as Biofilters in Aquaculture 184

Questions 188

Oyster Biology and Culture in India

xiii

12. Strategies for Development of Oyster Culture 189

Oyster Resources 189

Biology 190

Natural Seed 190

Hatchery Seed 190

Nursery Rearing of Seed 191

Genetics 191

Grow out Culture 192

Economics 194

Social Considerations 194

Technology Transfer 194

Market 1 95

Questions 195

References 196

Index 232

A v

■

Chapter 1

Introduction

OYSTERS are bivalve molluscs occurring worldwide in temperate,
subtropical and tropical seas. Generally they inhabit the coastal waters.
Certain species of oysters also occur in lagoons, estuaries and backwaters.
They are endowed with a pelagic larval life which ensures wider distribution.
The larvae settle on hard substrates such as rocks, molluscan shells or on firm
bottom areas, undergo metamorphosis and lead sedentary life. Oysters are
filter feeders, feed low in the food chain and play a crucial role in the coastal
ecosystem. The soft body parts of the oyster are enclosed within two shells
which protect the animal from external disturbances. Oyster meat is nutritious
and rich in protein and minerals.

From time immemorial, the oysters are traditionally eaten in many parts
of the world and are currently among the high priced seafoods in many
temperate countries where consumption of raw oysters is very popular. They
are exploited from the natural beds and are also farmed on a large scale in
many countries. In view of their economic importance oysters are the objects
of intensive studies by a large number of workers. Angell (1986) stated that
“The oyster is probably the most studied invertebrate organism and much is
known about its biology”. During 2003, the world production of oysters by the
harvest of natural populations was estimated at 1,99,517 mt and through
aquaculture at 44,96,609 mt. Among the oysters, Crassostrea (Sacco) is by far
the most important genus. The Eastern oyster, also called American oyster,
C.virginica (Gmelin) formed a significant portion (83.5%) of the production
by the harvest of wild stocks while the Pacific oyster, C.gigas (Thunberg) is
the most dominant among the farmed oysters accounting for 97.3% of world
oyster production in 2003 (FAO, 2003a; 2003b).

The oyster fisheries in many parts of the world have declined due to habitat
destruction, pollution, diseases and overfishing. Historically, the growth and
decline of the Eastern oyster, C.virginica fishery in the Chesapeake Bay, USA
is perhaps the best documented. The oyster catch peaked in Maryland at
6, 1 5,000 1 in 1 884 and declined to 1 2,000 1 in 1 992. The decline was attributed
to ‘reduced water quality’, diseases and fishing (see Rothschild et al, 1994).
Habitat destruction by using dredges for harvest and overfishing were considered
as prime factors by Rothschild et al (1994). For the recovery of the fishery
these authors suggested a 4 - point strategy namely: ( 1 ) fishery management (2)
replenishment (3) habitat replacement and (4) broodstock sanctuaries.

Oyster Biology and Culture in India

Oyster fanning has a long history as reported by Guo et al (1999), and the
Chinese cultured oysters since more than 2000 years ago. Bardach et al
(1972), stated that “Marine aquaculture may well have begun with oysters,
which were cultivated in Europe during Roman times”. In Japan, oyster
culture began in 1670 in the Hiroshima Bay (Imai, 1977). Newkirk (1991)
stated that oysters are cultured on every continent except Antarctica. Oyster
culture began by collecting oyster seed on stones and similar hard materials
(cultch) and relaying the cultch on firm grounds. There was little management
practice involved and the production was low. This was followed by the stick,
stake and rack culture methods which were independent of the nature of
substratum and gave higher production when compared to the on-bottom
culture. By 1950s with most of the shallow coastal grounds used for oyster
farming, the Japanese initiated raft and longline culture extending up to 30 m
depth. When compared to rafts, longlines were found better suited to withstand
the rough sea conditions in coastal waters. Extension of the farming grounds
into deeper waters resulted in substantial increase in the production of oysters
in Japan. Hatchery technology for oyster seed production was developed in
1950s.

China has emerged as the world leader in oyster farming accounting for
84% of production in 2003 followed by Japan (5.8%), Korean Republic
(5.3%), France (2.6%) and the USA (2.4%). Several technological advances
have been made in oyster culture in recent years, particularly in temperate
countries. Following the success of oyster culture in these nations, and in the
context of increasing demand of the commodity, the tropical countries also
evinced keen interest to develop oyster culture where it is practiced as a small-
scale activity. The tropical countries have the advantage of faster growth rate
requiring only 6-8 months of culture against 2-4 years in many temperate
countries. Besides, low production cost due to cheap labour is also a favourable
factor. The major problems faced by the oyster culture industry include
pollution, diseases and continuous high stocking density culture in the same
site, exceeding the carrying capacity of the water body. Low domestic market
demand is a constraint in some countries.

In India, the first attempt to bring together the available information on
oyster resources was made by Alagarswami and Narasimham (1973) followed
by Rao (1974). The Central Marine Fisheries Research Institute brought out
a comprehensive account on oyster resources, biology and culture in a Bulletin
entitled 'Oyster Culture: Status and Prospects’ (CMFRI, 1987). Rao et al.
(1992) described the technology of seed production and farming of Crassostrea
madrasensis and James and Narasimham (1993) gave an account on oyster
culture in a Handbook on farming of molluscs in India. Narasimhan et al
(1993) gave an overview of the molluscan resources of the country which
included oysters. Joseph (1998) dealt on oyster culture in the tropics, which
included India. Recently Appukuttan et al (2000) gave an update account of

Introduction

oyster culture along with the mariculture of other bivalves in the country while
Muthiah et al (2000) gave information on oyster culture. Kripa et al. (2004)
described the development of oyster farming as a rural development program
in Kerala especially as a group farming activity.

Among the Indian oysters, Crassostrea madrasensis is the most dominant,
occurring in the estuaries, bays and backwaters along the east coast and
south-west coasts (. Fig.l. ). Oysters are harvested at low tides in shallow
waters by dislodging them with a chisel and hammer. Oyster fishing is a small-
scale activity in the country. Many preparations are made with cooked oyster
meat and it is also processed into several products. The oyster shell finds
application in lime-based industries. The average annual production of oysters
by fishing for the period 1995-1999 from the country was estimated at 18,800
tonnes (CMFRI, 2001). This reflects substantial increase in production when
compared to mere 1000 tonnes/year reported for 1980s by Alagarswami and
Meiyappan (1989).

Fig.l. The oyster Crassostrea madrasensis with one valve removed to show the
meat in shell

Courtesy: CMFRI, Cochin, Kerala

During 1970s work on oyster culture was taken up at the Tuticorin
Research Centre of CMFRI, Tuticorin. Methods of natural spat collection,
grow out culture by using trays and rens held on or suspended from racks were
developed. With the setting up of the Shellfish hatchery in 1980 at Tuticorin,
oyster spat were successfully produced in 1982 (Nayar et al., 1984). This
hatchery at Tuticorin played a significant role in providing oyster seed to
undertake location testing studies to find out their suitability for culture, at

Oyster Biology and Culture in India

several places along the Indian coast. The very first attempt in 1993 to test the
suitability of the Ashtamudi Lake in Kerala for oyster culture proved successful.
In 1994, the CMFRI has set up a rack and ren oyster culture demonstration
farm in the Ashtamudi Lake. This water body proved to be a very good site
for oyster seed collection. The first commercial oyster farm was set up in 1996
by an enterprising farmer in the Ashtamudi Lake, close to the demonstration
farm of CMFRI, followed by several villagers venturing into oyster culture in
the estuaries of Kerala. Beginning in 1980s at Tuticorin and since 1995 at
Ashtamudi, the CMFRI is conducting training programmes covering all aspects
of oyster culture to farmers and others, lending technology support and is
linking the farmers with developmental agencies for finance and marketing.
The rack and ren method of farming is adopted by the farmers. The annual
production of farmed oysters ( C.madrasensis ) in India is estimated to be
between 750-800 tonnes.

In India, coastal aquaculture is at present mainly centered around shrimps,
largely due to their high price, demand in the export trade and the technological
advancements made in breeding, seed production and field culture. However,
over the past decade, frequent disease outbreaks and negative environmental
impact of their culture in coastal areas have greatly hampered the accelerated
expansion and extension of this sector. In this context, entrepreneurs and
farmers are attempting to diversify the farmed species, and oysters are among
the most preferred species, in view of their biological characteristics, adaptive
capacity to varying environmental conditions, growing demand in export
market and enlarging acceptance by the domestic consumers. In this scenario,
the foremost requirement of developing oyster culture on a scientific and
sustained basis is the availability of information on different aspects of its
culture and the related paradigm. This book on oyster biology and culture in
India endeavours to meet this requirement. It is mainly written to cater to the
needs of university teachers, researchers and students in India. It is also useful
to a wide spectrum of personnel drawn from Fisheries / Rural Development
Agencies, Financial Institutions, NGOs and entrepreneurs. In the chapters
presented in this book the emphasis is chiefly on the status of oyster culture
in India. Also the progress made in oyster culture in the major oyster producing
countries of the world is briefly reviewed. The recent technological advances
made in other countries in the hatchery production of seed and grow out
culture have been dealt with. In the light of the developments in oyster culture
in other countries, the gaps in knowledge, future research needs, constraints
faced by farmers and the steps to be taken for the development of oyster
resources and culture on a sustainable basis in the Indian context are highlighted.

The production of figures in tonnes by weight given in this book are in
metric tonnes.

QUESTION

1 . Write briefly on the development of oyster culture in India

Chapter 2

Oyster Resources,
Distribution and Ecology

OYSTERS are placed under the Class Bivalvia which encompasses aquatic
molluscs that show a fundamental bilateral symmetry. Oysters inhabit
the littoral and shallow subtidal areas. Their distribution extends to wide range
of ecosystems including the coral reefs, mangroves and rocky shores. The
species identification of these bivalves has been very difficult due to exceedingly
variable morphological features of the shell, influenced by the environmental
variation and the nature of substratum. In the last two decades considerable
effort has been put in to revise the taxonomy of oysters based on the external
shell morphology, anatomical characters of soft body parts and electrophoretic
studies. Another thrust area of molluscan research is to evaluate the ecological
significance of oyster assemblages. Studies have shown that oyster reefs play
a critical role in enhancing the species richness of the habitat and are now
considered as Essential Fish Habitats (EFH). A brief description on the
taxonomy, distribution and ecology of oysters is given below.

TAXONOMY

Considerable work has been done on the taxonomy of oysters (Thomson,
1954; Carreon, 1969; Stenzel, 1971; Ahmed, 1975; Carriker, 1976; Torigoe,
1981;Angell, 1986; Harry, 1986; Arakawa, 1990). About one hundred species
of living and five hundred species of extinct oysters were recognized initially
(Korringa, 1952). Later it was realized that most of the species were not valid.
In 1955, the International Commission on Zoological Nomenclature (ICZN)
stated that the nominal species Gryphea angulata was not the type species of
any nominal genus and the generic name Crassostrea (Sacco, 1897) was
available for use for that species. Consequent to this many important oysters
were placed under the genus Crassostrea.

Stenzel (1971) in his treatise on the systematics of oysters recognized
eight living and fossilized genera. Several generic names have been introduced
in recent years. Harry (1985), after an exhaustive study based on the morphology
of shell and soft parts of oysters, found it necessary to extend the classification
beyond that proposed by Stenzel (1971). This revised classification has resulted
in the synonimyzation of names of oysters in several geographic regions that
are simply different populations of one species. Recently electrophoretic

Oyster Biology and Culture in India

investigations on the population genetics of several species of oysters have
been attempted (Buroker etal., 1983; Newkirk, 1980; Hedgecock and Okazaki,
1984; Klinbunga et al. 2000).

Diagnostic characters

The shell is irregular in shape, more or less inequivalve, and is permanently
attached to the substrate. Unlike the mussels and scallops which attach by
byssus threads, the oysters are cemented by the left valve to the substrate. This
sedentary mode of life has led to atrophy of foot and byssal gland. Oysters are
characterised by single adductor muscle, hinge without teeth, pallial lobes free
with marginal tentacles and pallial line without sinus, obscure or absent.

Classification

Oysters come under Phylum Mollusca, Class Bivalvia (also called as
Pelecypoda, Lamellibranchiata or Acephala), Order Mytiloida, Super Family
Ostracea.

Currently the living species of oysters are grouped into two families,
Ostreidae and Gryphaeidae. The identifying characters of these two families
are given in Table 1 (Fig. 2).

Table 1. Distinguishing characters of Gryphaeidae and Ostreidae

Gryphaeidae Ostreidae

Shell structure vesicular
Adductor muscle circular

Adductor muscle placed closer to
the hinge than to the ventral margin

Chomata long, sinuous and branched

Shell structure not vesicular

Adductor muscle scar oval or kidney
shaped

Adductor muscle median in position or
placed nearer to the shell margin

Chomata if present short and simple

The oysters coming under the family Ostreidae are grouped into three
subfamilies namely Ostreinae, Crassostreinae and Lophinae. The species
coming under Crassostrinae have a promyal passage, are non incubatory and
the shell is chalky. In Ostreinae and Lophinae the promyal passage is absent
and they incubate the young ones for a short period. The shell is chalky in
Ostreinae while in Lophinae it is not chalky.

Based on the shell characteristics, shape, size, colour and the
anatomical features of the promyal chamber, gill ostia, heart, gut and breeding
habits, the various genera and species are identified. The identification characters
of some of the important oyster genera coming under Ostreidae and Gryphaeidae
as described by Quayle and Newkirk (1989) and FAO (1998) are given below.

Crassostrea: Chomata absent. Adductor muscle scar reniform and variously
coloured according to the species. Chalky deposits often present on the shell.
Promyal chamber present. Fairly large oysters upto 200 mm having wider

Oyster Resources, Distribution and Ecology

Fig. 2. Internal shell characteristics of Gryphaeidae and Ostreidae

distribution than the flat oysters and have the ability to tolerate wide variations
of the environmental conditions.

Ostrea: Small and inconspicuous chomata present near hinge region.
Right valve usually flat, left valve with small radial plicae. The nacre often
coloured, scar reniform, promyal chamber absent. Moderate to large size. Less
tolerant to salinity variation than Crassostrea.

Saccostrea: Chomata present, often completely around the periphery.
Left valve plicate. Muscle scar reniform and generally coloured. Promyal
chamber present. Medium sized oysters. Habitat similar to Crassostrea.

Tiostrea: Chomata present in the young but disappears with age. Adductor
muscle scar reniform. Medium sized oysters. Larviparous oysters.

Striostrea: Characterized by full left valve attachment. The right valve
with brittle lamellae. Large, elongate and chomata present. Large oysters upto
200 mm. Found in shallow subtidal areas.

Hyotissa: Oysters with thick valves. Promyal chamber present. Posterior
margin deeply folded. Large oysters growing upto 200 mm. Widely distributed
in subtidal tropical rocky regions and coral reefs.

Lopha: Surface of both the valves roughened by numerous small low and
rounded protruberances arranged in obscure radial rows. Imbricating scales
absent.

Dendostrea: Surface of both valves without small low and rounded
protuberances, imbricating growth scales often present. Left valve with recurved
spines forming clasping shelly extension for attachment of shell to extraneous
object.

Oyster Biology and Culture in India

Alectyronella: Valve margins strongly plicate, chomata forming 2 to 4
rows of numerous pustules in right valve only; fingerprint shell structures
generally present.

Planostrea : Chomata restricted to the dorsal half of the internal shell
margins. Valve margin smooth.

In the last century considerable effort was made to identify and place the
living oysters in south-east Asia in appropriate taxonomic position. In the Gulf
of Thailand and the Andaman sea, nine species of oysters viz. Hyotissa hyotis,
Parahyotissa (Parahyotissa) imbricate (Gryphaeidae), Crassostrea belcheri,
Crassostrea iredalei, Saccostrea cucullata, Saccostrea forskali, Striostrea
(Parastriostrea) mytiloides, Lopha cristagalli and Dendostre a folium have
been identified by Yoosukh and Teerapang (1998). Genetic diversity and
species-diagonostic markers of C. belcheri, C. iredalei, S. cucullata, S. forskali
and S. mytiloides were investigated by the randomly amplified polymorphic
DNA- RAPD analysis (Klinbunga etal, 2000). Nine species-specific markers
in C. belcheri, 4 in C. iredalei and 2 in S. cucullata were identified. Genetic
distances between pairs of oyster samples were between 0.105 and 0.011. A
neighbour joining tree indicated distant relationships between Crassostrea
and Saccostrea oysters, but closer relationships were observed between the
latter and Striostrea mytiloides. The commercially important species are mostly
in the family Ostreidae.

Indian oyster resources

Along the Indian coast, oysters were identified and studied since the beginning
of the 20th century. One of the first records on the taxonomy of Indian oysters
is by Hornell (1910 a). Since then a series of reports on the taxonomy of Indian
oysters were made by Annandale and Kemp (1916); Preston (1916); Gravely
(1941); Satyamurthi (1956); Durve (1968); Rao (1974); Rao (1987) and Rao
et al. (1992). The Indian oysters were originally referred to the genus
Ostrea, but later included under the genus Crassostrea. Apart from this,
occurrence of another oyster genus Saccostrea was also recorded. The generic
characters of Crassostrea and Saccostrea have been described above. In India,
four species of oysters have been considered as economically important (Rao
et al, 1992), which come under the subfamily Crassostrinae. They are
Crassostrea madrasensis (Preston), Crassostrea gryphoides (Schlotheim),
Crassostrea rivularis (Gould) and Saccostrea cucullata (Born). The detailed
description of the four species based on the above mentioned literature are
given below.

Crassostrea madrasensis ( Preston , 1916): Shell valves usually elongate, and
very irregular in shape. Outer surface of shell with numerous foliaceous
laminae with sharp edges. Left valve is deep and slightly concave. Hinge
narrow and elongate; sometimes elevated with a median depression. Adductor

Oyster Resources, Distribution and Ecology

Fig. 3. Left and right valves of Crassostrea madrasensis

muscle scar situated subcentrally, reniform and dark purple in colour. Colour
of outer surface of shell grey, green or light purple (ecophenotypic variations).
Inner surface of valves is smooth, glossy and white in colour with purplish
black colouration along the margin of the valves. (Fig. 3)

Crassostrea gryphoides (Schlotheim, 1813): Shell valves elongate and thick.
Left valve cup like, hinge area well developed with a deep median groove with
lateral elevations. Denticles not present on the inner margin of valves. Adduc¬
tor muscle scar is broad, more or less oblong (Fig. 4. A). Striations on the scar
are obscure or absent. Inner surface of valves and adductor muscle scar pearly
in colour .

Crassostrea rivularis (Gould, 1861): Shell valves large, roughly round and
flat. Shell cavity is shallow. Left valve is thick and slightly concave and the
right one is almost the same size or slightly larger. Adductor muscle scar is
oblong and white or smoky white in colour (Fig. 4.B). Inner surface of valves
is white and bright.

Saccostrea cucullata (Born, 1778): Shell valve hard and stony, trigonal or
pear shaped. The left valve is deep or moderately deep. Right valve is flat or
slightly convex. Hinge straight, umbonal cavity well developed. Margins of

Oyster Biology and Culture in India

Fig. 4. Inner view of left valves of A, Crassostrea gryphoides; B, Crassostrea
rivularis ; C, Saccostrea cucullata (hn, hinge; ams, adductor muscle scar)

both the valves have well developed angular folds sculptured with laminae.
Small tubercles present along inner margin of the right valve and there are
corresponding pits in the left valve. Adductor muscle scar is kidney shaped,
striated and white or greyish in colour (Fig. 4.C). Outer surface of shell pale
white, grey, light brown, green or purplish. Inner surface white.

Rao et al. ( 1 996) have mentioned that Crassostrea rhizophore (Guilding)
occurs in stray numbers in the mangroves of Tamil Nadu. In addition to these
five species of oysters coming under the family Ostreidae, one species under
Gryphaeidae has also been reported from India. The Giant oyster, Hyotissa
hyotis (Linnaeus) with large robust shell is found in the coral reefs. Incubatory
or larviparous oysters have not been reported from Indian waters (Rao et al,
1992).

As mentioned earlier, in the absence of well established taxonomic status
of different species of oysters, there exist varying opinions as regards the
nomenclature, identity and synonymy of the species by different workers. Rao
(1987) has listed the synonyms of the Indian oysters. For further synonyms
and discussions on this aspect the readers may refer to Stenzel (1971), Torigoe
(1981) Harry (1985), Coan et al. (1995) and Carriker and Gaffney (1996).
Iorigoe (1981) considered C. rivularis and C.ariakensis as the same species,
but this is probably incorrect usage (Coan etal., 1995). Harry (1985) concluded
that rivularis is a junior synonym ol pestigris and placed pestigris in the new
genus Planostrea.

DISTRIBUTION OF OYSTERS

Oysters are widely distributed in the temperate and tropical waters. Though
they are common in the shallow intertidal and subtidal zones of coastal waters
(Galtsoff 1964; Mahadevan 1987) their occurrence in deeper areas has also

Oyster Resources, Distribution and Ecology

been reported. Neopycnodonte cochlear commonly known as deepsea
oyster or spoon oyster lives in depths extending from 27 to 2,100 m (Harry,
1985).

Commercially important oysters

Some of the commercially important oysters and their distribution summa¬
rized from Quayle and Newkirk (1989) and Carriker and Gaffney (1996) are
given below. The taxonomic designations are mainly based on the most
commonly used species names as found in literature and should not be taken
as the last word on nomenclature.

Crassostrea gigas (Thunberg, 1793)

Common name: Giant Pacific oyster, Miyagi oyster, Magaki
Distribution: Indo-west Pacific from Pakistan to Japan and Korea and the
Philippine Islands, Borneo and Sumatra, all along the China coast . Introduced
to west coast of Canada, United States, Mexico, Chile, Korea, Taiwan and
New Zealand.

Economic Importance: One of the most important food oyster; widely
farmed especially in Japan, Korea, west coast of United States, Canada
Europe, Brazil, Chile and Ecuador.

Crassostrea rivularis (Gould, 1861)

Common name: Chinese oyster
Distribution: Japan, China, Pakistan, India
Economic Importance: Cultured in China

Crassostrea belcheri (Sowerby, 1871)

Common name: Malaysian oyster
Distribution: Southeast Asia

Economic Importance: A large rapidly growing oyster and experimentally
cultured. Principal commercial species in Southeast Asia .

Crassostrea iredalei (Faustino, 1932)

Common name: Slipper shaped oyster, talabang, tsinelas
Distribution: Philippines, Southeast Asia

Economic Importance: Important fishery on east coast of Malaysia,
widely cultivated in Philippines; a commercial species in Southeast Asia .

Crassostrea madras ensis (Preston, 1916)

Common name: Indian backwater oyster

Distribution: Sri Lanka, India, South China sea coasts, Pakistan
Economic Importance: Commercial species in India, commercially farmed
in India (Appukuttan et al., 2000).

Oyster Biology and Culture in India

Crassostrea virginica ( Gmelin , 1791)

Common name: Eastern oyster

Distribution: Western Atlantic from Gulf of St. Lawrence in Canada to
Gulf of Mexico, Carribbean and coasts of Brazil and Argentina

Economic Importance: Occurs naturally in some areas as extensive reefs
on hard to firm bottoms; commercially important; extensively exploited;
widely farmed.

Crassostrea columbiensis (Hankey, 1845)

Common name: Columbian oyster

Distribution: Eastern Pacific from Chile north to Gulf of California.
Economic Importance: Commercial species from the Gulf of California
to Panama, cultured in Mexico.

Crassostrea rhizophorae ( Guilding , 1828)

Common name: Mangrove oyster
Distribution: Gulf of Mexico, Caribbean, Brazil

Economic Importance: Cultured on the Caribbean coasts. In Brazil
cultivated on a pilot scale by family enterprises.

Crassostrea gasar ( Adanson , 1757)

Common name: West African mangrove oyster
Distribution: Central West Africa, Senegal to Angola .

Economic Importance: Economically important in Gambia. Harvested
from wild. Experimentally cultured in Senegal .

Crassostrea angulata ( Lamarck , 1819)

Common name: Portuguese oyster

Distribution: Eastern Atlantic from equater north to Mediterranean and
Atlantic coast of Iberian peninsula, Japan, China, Pakistan, India
Economic Importance: Widely cultivated in southern Europe

Crassostrea paraibanensis ( Singarajah , 1980)

Distribution: Northern Brazil

Economic Importance: Was previously confused with and still locally
called C.brasiliana. Cultured commercially in north-eastern Brazil.

Dendostrea folium (Linne, 1758)

Common name: Bronze oyster, Cox-comb oyster, flat oyster, leaf oyster,
imbricated oyster

Distribution: Widely distributed in Indo-Pacific region.

Economic Importance: Experimentally cultured in Malaysia; some
harvesting from wild populations in Morocco to Gabon area of western
Africa.

Oyster Resources, Distribution and Ecology

Hyotissa hyotis ( Linne , 1758)

Common name: Honey comb oyster, hyoid oyster, giant oyster
Distribution: Tropics of Indo-West Pacific and eastern Pacific
Economic Importance: Commercial species in the tropics. Harvested
from wild populations

Lopha cristagalli (Linne, 1758)

Common name: Cock’s comb oyster

Distribution: Mediterranean Indo-west Pacific, east coast of Africa and
Red sea to Ryuku Islands, Philippines, Indonesia and rare in northern Australian
waters.

Economic Importance: Associated with coral reefs at depths of a few
meters.

Ostrea edulis Linne , 1 758

Common name: Edible oyster, European flat oyster
Distribution: Eastern Atlantic from Norway and British Isles to Morocco
and Mediterranean and Black seas, Aegean and Marble seas .

Economic Importance: Cultivated since ancient Roman times; farmed in
France, Netherlands, United Kingdom and Spain.

Saccostrea commercialis (Iredale and Rough ley, 1933)

Common name: Sydney rock oyster

Distribution: East coast of Australia, New Zealand and Thailand
Economic Importance: Widely farmed in eastern Australia and New
Zealand. Introduced to Hawaii.

Saccostrea cucullata (Born, 1778)

Common name: Bombay oyster, Indian rock oyster, Red sea oyster
Distribution: Tropical coast of west Africa and offshore islands, around
Cape of Good Hope, Indo-west Pacific to southern Japan, southern and
Western Australia, northern New Zealand, all along Chinese coast, and
Philippines .

Economic Importance: Commercial species in Indian Ocean and South¬
east Asia.

Saccostrea echinata (Quoy and Gainard, 1834)

Common name: Black bordered oyster

Distribution: South-east Asia, Japan, Australia, Indian Ocean and Western
Pacific Islands.

Economic Importance: Widely cultivated in Indian Ocean and South¬
east Asian countries.

Oyster Biology and Culture in India

Saccostrea glomerata (Gould, 1850)

Common name: New Zealand rock oyster

Distribution: New Zealand, Hong Kong, Pakistan and Arabian Sea
Economic Importance: It is the main commercial species in New Zealand

Striostrea prismatica (Gray, 1825)

Distribution: Mexico and Pacific coast of Columbia
Economic Importance: Cultured experimentally in the Pacific coast of
Columbia.

Distribution of oysters in India

The distribution of oysters along the Indian coast shows a distinct pattern (Fig.
5). C.madrasensis is the major oyster species found along the east coast,
except West Bengal, from Orissa to Tamil Nadu (Mahadevan, 1987; Das,
1993; Narasimham et al., 1993; Rao et al., 1996). Along the west coast it is
more dominant in the south than in the north (Mahadevan, 1987). C.gryphoides
is the main oyster species in the north-west region especially in the Gulf of
Kutch. Mixed populations of C.gryphoides and C.rivularis are seen along the
north-west coast (Chhaya et al., 1993). One interesting observation is that
though distribution of C.gryphoides is restricted to north-west region,
occurrence of its fossils has been recorded from Calcutta (Durve, 1986).
Saccostrea cuccullata has wider distribution and is found along with all the

Fig. 5. Locations showing the distribution of commercially important oyster spe¬
cies in India (after Rao et al., 1992)

Oyster Resources, Distribution and Ecology

species of the genus Crassostrea occurring in India (Mahadevan, 1987; Joseph
and Joseph, 1988; Sundaram, 1988; Rao et al., 1996). Along the east and
south-west coast, it coexists with C.madrasensis (Rao et al ., 1996) while
along the north-west coast it is seen along with C.gryphoides (Chhaya et al.,
1993). Apart from this, oyster populations dominated by S.cucullata are also
seen especially in Karnataka (Joseph and Joseph, 1988), Maharashtra
(Sundaram, 1988) and Gujarat (Chhaya et al., 1993). This species is also
widely distributed in the inshore waters of Andaman and Nicobar islands.

C.madrasensis has been found to be morphologically similar to the
American oyster. Durve (1986) has critically analyzed the distribution of
C.madrasensis, its morphological and biochemical similarity to the other
major Crassostrea species and vis-a-vis commented “it thus could be conjured
that C.madrasensis, C.gigas, C.gryphoides, C.virginica are all closely related
and may have emerged as independent species by geographic separation and
subsequent isolation.” He also hypothesized that the extension of distribution
of C.gryphoides and C.rivularis to the south-west coast of India might have
been prevented by the now extinct land bridge from India to Madagascar.

Horizontal zonation

Within an estuary, horizontal zonation of different oyster species in a population
has been observed. In most estuaries, Saccostrea cucullata is found more in
the marine environment (Rao, 1987). In the Ashtamudi Lake in Kerala, near
the barmouth, S.cucullata occurs in dense concentrations contributing to
81.7% of the total oyster density, the rest being C.madrasensis. Towards the
estuarine region, the density of this species becomes thin and forms only 15
to 1 9% of the total oyster population. C.madrasensis dominates in the estuarine
region and, towards the river side S.cucullata is completely absent (Kripa,
1998). This zonation pattern from marine to brackishwater can be due to the
better adaptive capacity of C.madrasensis to low saline condition than
S.cucullata, i.e. due to the difference in the lower threshold of their salinity
tolerance. In the intermediary zone between the two extremes of marine and
estuarine conditions the two species occur together..

Density of oysters

High densities have been observed in the natural beds during the spat fall
season. In the Pulicat Lake and Ennore backwaters, the density of spat has
been found to range between 300 to 1500 nos/ m2 and 90 to 1800 nos/ m2
respectively. The density of oysters in different estuaries along the Indian
coast is given in Table 2.

Relative abundance of oyster resources

The magnitude of oyster resources shows wide variation along the Indian
coast mainly due to seasonal variations in the hydrographic conditions of the

Oyster Biology and Culture in India

Table 2. Oyster densities (nos/ m2) in different oyster beds along the Indian coast

State

Location

Species

nos/ m2

Reference

Gujarat

Sikka

S. cucullata

142

Chhaya et al. (1993)

Maharashtra

Bandra

S. cucullata

576-1,792

Sundaram (1988)

Worli

S. cucullata

256-1,536

Karnataka

Kalinadi estuary

S. cucullata

12 -150

Ramachandran

C. madrasensis

nil-0.7

(1988)

Chendia creek

S. cucullata

C. madrasensis

0.5

Mulki estuary

S. cucullata

15 to 320

Joseph and Joseph
(1988)

Kerala

Ashtamudi Lake

C. madrasensis

14-104

Kripa (1998)

S. cucullata

43-258

Tamil Nadu

Muttukadu

C. madrasensis

60-320

Sarvesan et al.

backwaters

(1988)

Pulicat Lake

C. madrasensis

7 - 298

Thangavelu and
Sanjeevaraj (1988a)

C. madrasensis

300-1,500

Rao et al. 1 996

Ennore estuary

C. madrasensis

90-190

Rao et al. 1 996

Pondicherry

Chunnambaru

estuary

C. madrasensis

160 -3,010

Rao et al. 1 996

oyster beds (Rao et al. , 1996). During 1987 -90, the Central Marine Fisheries
Research Institute (CMFRI) made an effort to assess the standing stock along
the south-east and south-west coasts of India through planned surveys (Rao et
al., 1996). Apart from this, information on the resource abundance of selected
regions of Orissa, Karnataka, Maharashtra and Gujarat is available from the
works of Ramachandran (1988), Sundaram (1988), Das (1993) and Chhaya et
al. (1993). From other states information on oyster resources is not available.
Following is a brief report on the oyster resources of different maritime states
of India.

Orissa : The Bahuda estuary near Sonapur harbours a rich bed of
Crassostrea madrasensis. Mahadevan (1987) has indicated that oysters were
seen in approximately 5 ha area in Sonapur. Recently, Das (1993) stated that
the oyster beds extend to an area of 128 acres.

Andhra Pradesh: The total area of the oyster beds in this state, spread in
11 estuaries is 28.54 ha (Table 3). C. madrasensis is the main resource.
Saccostrea cucullata formed 30 % and 10% of the oyster population in
Kakinada harbour area and Kandaleru estuary respectively. The Pennar estuary
has the richest oyster bed of 3.2 ha with a population of 727 t followed by
Peddapatnam Revu and Kandaleru estuary. Rao etal. (1996) have commented
that oyster resources at certain localities in this state are limited due to
turbidity and fast water flow.

Oyster Resources, Distribution and Ecology

Table 3. Estimated standing stock of oyster in Andhra Pradesh during 1990

Location

Total area of beds
(ha)

Total stock
(tonnes)

Length range
(mm)

Uppada creek

17.6

12-117

Kakinada harbour

0.74

Kakinada Port

0.60

Peddapatnam Revu

0.25

486

Machilipatnam creek

0.40

16.8

28-59

Mudugondi estuary

1.26

Gundalakamma estuary

0.27

4.1

Pennar estuary

3.20

727

Kandaleru estuary

1.80

88.7

Swarnamukhi estuary

7.3

Konderu estuary

0.02

1.8

Total

28.54

1,554.3

Source: Rao et al. (1996)

Tamil Nadu and Pondicherry

The total standing stock was estimated at 19 1 65.6 1 in 243.6 ha area. Cmssostrea
madrassensis is the major resource in most of the estuaries though in some
estuaries like Uppanar, Gadilam, and Alambau, Saccostrea cucullta formed
10 to 32 % of the population. Crassostrea rhizophore was found in the
Coleroon estuarine complex attached to the roots of mangroves. The Ennore
estuary had the richest oyster beds with an estimated standing stock of 14, 379
tonnes spread over 45.8 ha (Table. 4). In Pondicherry, the Chunnambaru
estuary had the maximum oyster resource, 2219.6 tonnes in 54.4 ha. In almost
all the estuaries large size C.madrasensis (>100 mm) were seen. Rao et al.
(1996) have attributed the reasons for such abundance to low rainfall and
moderate current action in the vicinity of oyster beds. These conditions are
favourable for breeding, spatfall and growth of oysters. In a survey conducted
during September-December 1986 Sarvesan et al. (1988) the stock of
C.madrasensis in 3.61 ha beds at 545 metric tonnes in Muthukadu backwaters.
Sreenivasan et al. (1996) reported that a survey conducted on 13 and 14
September 1995 revealed the presence of C. madrasensis stock of 3,712
metric tonnes in 25.2 ha oyster beds. They measured 35-141 mm in length.

Kerala: The standing stock of oyster was estimated as 3938 tonnes in 30.
8 ha spread in 1 1 estuaries (Table 5). Though C. madrasensis was the major
resource, S.cucullata formed 21 to 35% of the oyster population in estuaries
like Shriya, Murad, Beypore, Chaliyam, and Nileswar. Most of the estuaries
had limited oyster resource. Korapuzha estuary is the richest with 3,664
tonnes in 27 ha contributing to more than 93% of the State’s oyster resource.
The length, total weight and meat weight of the oysters recorded in most
estuaries was smaller than that of Tamil Nadu. While the length of

Oyster Biology and Culture in India

Table 4. Estimated standing stock of oyster in Tamil Nadu and Pondicherry during 1 988
-1990

Location

Total area

of beds
(ha)

Total

stock

Length
range
(mm )

Average

total

weight (g)

Average

meat

weight (g)

Pulicat Lake

10.3

10.4

18-167

5.3

Ennore estuary

45.8

14,379

24-208

6.2

Kovalam backwaters

3.1

4.2

22-143

4.9

Edayar backwater

2.0

3.5

36-177

5.6

Alambaru estuary

11.0

715

30-77

2.1

Chunnambaru estuary

54.4

2219.6

12-128

3.4

Gadilam estuary

8.9

29.5

29-126

3.1

Uppanar estuary

18.7

147.1

31-109

4.2

Vellar estuary

50.1

456.9

27-123

3.4

Coleroon estuary

30.5

391.5

14-148

Vellayar estuary

2.4

5.0

58-163

148

4-12

Vettar estuary

1.4

2.6

31-121

Transquebar

0.6

25.6

55-124

Athankarai estuary

1.7

380.8

61-138

128

Kanjirangudi estuary

0.2

19-123

Kallar estuary

0.1

61-103

Karapad creek

0.5

84.9

71-122

143

Korampallam creek

1.1

272

70-133

136

9.5

Palayakayal estuary

0.2

2.6

75-136

131

Pinnakayal estuary

0.6

31.4

28-133

Total

243.6

19,165.6

C.madrasensis in Tamil Nadu ranged between 12 to 208 mm in Kerala it was
17 to 1 18 mm. Similar difference was observed in the case of S.cucullata also,
the length ranges being 15 to 70 mm in Tamil Nadu and 13 to 52 mm in Kerala.

Karnataka: Several estuaries in Karnataka harbour resources of C.
madrasensis and S.cucullata. Mahadevan (1987) has reported that Nethravathi,
Sharavathi and Kali estuaries, have oyster beds ranging from 1 to 5 ha.
Ramachandran (1988) has estimated the standing stock of the Kalinadi and
Chendia estuaries of Karnataka as 1 .2 and 2.2 tonnes in 0.65 ha and 2.0 ha area
respectively. The population is composed of both C.madrasensis and S.cucullta.

Goa: Oyster settlement has been reported from Ribander, Siolim and
Curca (Mahadevan, 1987). However, the extent of the oyster beds and their
abundance has not been studied in detail.

Maharashtra: C.gryphoides has been reported from Dahanu creek, Boiser,
Satpuri, Palghar, Kelwa, Malad, Navapur, Utsali, Dahisar, Mahim creek,
Alibag, Purnagad, Ratnagiri, Jaytapur, Malwan, Worli, Versova, Marve,
Gobbunder, Cuff Parade, Bandra, Madh, and Bhate Bunder. In Mahim, Ratnagiri
and Jaytapur C.rivularis occurs along with C.gryphoides. S.cucullata is also
reported to occur along with these oysters. Sundaram (1988) has reported that

Oyster Resources, Distribution and Ecology

Table 5. Estimated standing stock (in tonnes) of oyster in Kerala in 1987

Location

Total area

of beds
(ha)

Total

stock

Length
range
(mm )

Average

total

weight (g)

Average

meat

weight (g)

Chandragiri estuary

0.5

26-62

Shiriya estuary

0.2

20-45

Nileshwar

0.4

36-102

10-150

Azhikkal

0.4

38-118

147

Murad estuary

0.5

26-55

Korapuzha estuary

3664

55-99

Beypore estuary

0.2

Chaliyam estuary

0.4

17-94

Periyar estuary

0.7

21-61

Thottapilly estuary

0.2

40-75

Kayamkulam estuary

0.3

31-73

Total

30. 8

3,938

NA= Not Available
Source: Rao et al ( 1996)

S.cucullata is the major species in the intertidal area of Worli and Bandra and
he estimated the stock at 335 tonnes in 8.75 ha.

Gujarat : C gryphoides is the dominant oyster species in Gujarat, followed
by S.cucullata and C.rivularis. Chhaya et al. (1993), have observed that the
oyster resource is very negligible in most parts of the coast. In some regions
the density is low, with about one oyster per m2 while the maximum has been
found to be 142 nos per m2. From the density of oyster beds, it can be inferred
that moderately rich oyster beds occur in Harshad Medha creek, Navibandar
and Sikka regions. Details are given in Table 6.

Andaman Nicobar Islands: C.madrasensis is found in Port Blair, Havelock
Island, Mayabunder and Dighlipur regions (James and Narasimham, 1993)

ECOLOGY OF OYSTER BEDS

Oysters live in a highly dynamic environment. With their sedentary habit they
are particularly vulnerable to the environmental perturbations. However, through
an array of physiological and behavioral mechanisms they have established
themselves as one of the successful estuarine species. The effect of
environmental variations such as salinity changes on oysters depends on the
range of fluctuations and the abruptness of these changes (Hand and Stickle,
1977). The ecology of some of the oyster beds of India has been studied and
the parameters such as temperature, salinity, turbidity and food availability
have been considered as most important and have received the maximum
attention (Homell, 1910a; Paul, 1942; Rao, 1951; Rao and Nayar, 1956;
Durve and Bal, 1962; Mahadevan and Nayar, 1987; Thangavelu and
Sanjeevaraj, 1988a ; Yavari, 1994; Kripa, 1998).

Oyster Biology and Culture in India

Table 6. Distribution of oyster resources in Gujarat during 1988-92

Location

Resource

Area surveyed
(ha)

Total oysters
(Nos.)

Katlwada

C.gryphoides

7.5

10,000

Namathi creek

C.gryphoides

0.5

1100

Sikka

S.cucullata

0.05

66,456

Gagawa

C.gryphoides

C.rivularis

1.17

200

Harshad Medha creek

C.gryphoides

41.55

90,000

Navibandar

C.gryphoides

22.50

75,000

Samadhiyani

C.gryphoides

3.50

3500

Datardi

C.gryphoides

1.0

6000

Umargoan

C.gryphoides

10.0

10,000

Khalwada

C.gryphoides

7.5

10,000

Source: Chhaya et al. (1993)

Temperature

Virtually every aspect of the oyster biology including feeding, respiration,
utilization of stored food reserves, reproduction, disease interactions, growth
and distribution is affected by temperature and salinity. Temperature variations
(range) observed in oyster beds along the east coast are : 27.5 to 34.5°C during
1975 -1976 at Athankarai ( Rao et al., 1987); 25.2°C to 31.93° C at Tuticorin
(1992-93) (Yavari, 1994) and 22.8° to 33.6° C at Kakinada Bay during 1985-
86 (Narasimham, 1987). In the Ashtamudi Lake in Kerala, the temperature
ranged between 28.2 to30.8°C during the period 1994 tol996 (Kripa, 1998).
The water temperature variations between 22.8 and 34.5°C are within the
normal distributional range of C.madrasensis. In high temperatures (> 41°C)
the oysters suffered mortality and weight loss (Fingerman and Fairbanks,
1955, 1957). The oysters were found to survive in intertidal temperatures of 46
to 49°C when immersed at low tide. Frequently inhibited pumping activity was
observed with rise in temperature. In some instances though the oysters kept
their valves open, the pumping rates were highly reduced (Shumway, 1996).

It has been observed that the combined effects of two or more environmental
variables can have profound biological consequences than any one of the
factors acting independently. In some estuaries along the east coast in summer,
the combined effect of high temperature and salinity and resultant desiccation
have caused oyster mortality (Mahadevan and Nayar, 1987; Rao et al., 1987;
1996). In south-west Louisiana and Texas the combination of high salinity and
temperature have caused mass mortalities of C.virginica (Owen, 1953).

Salinity

Butler (1949) has suggested that the single most important factor which
affects the oyster population is salinity. Salinity variations in estuaries may be
diurnal, seasonal, or spatial and changes may be abrupt or gradual.

Oyster Resources, Distribution and Ecology

How salinity influences the reproduction of oysters is described in Chapter
3. The annual variation of salinity in the oyster beds along the east coast has
been found to range between 3.49 and 35.01 ppt in Kakinada Bay during
1985-86 (Narasimham, 1987); 26.5 to 37.31 at Tuticorin during 1992-93
(Yavari, 1994). During 1975-1976 when the barmouth was closed, the salinity
reached as high as 71.62 ppt in Athankarai estuary (Rao et al. , 1987). Large
scale mortality of oysters due to continuous exposure to high salinity (>40 ppt)
has been reported by Rao and Nayar (1956) in Adayar estuary. Lowering of
salinity due to prolonged flooding during the north-east monsoon in certain
years has been reported to cause large-scale mortalities of oysters (Mahadevan
and Nayar, 1987). However, the recolonization of oysters and revival of oyster
beds have been observed in the subsequent years (Rao et al ., 1987).

Along the west coast, the oyster beds are more affected by low saline
conditions. The freshwater incursion into the estuaries during south-west
monsoon causes drastic changes in the oyster population. The annual variation
in salinity of the oyster bed was between 7.2 to 34.1 ppt during 1994-95 in
Ashtamudi Lake (Kripa, 1998). However, this has not caused mass mortalities.
In Cochin backwaters, very high mortality of oysters has been observed when
the salinity of the oyster bed remains below <1 ppt for a prolonged period
(Purushan et al ., 1983). Similar changes in oyster populations take place in the
estuaries of Karnataka due to salinity variation ( Joseph and Joseph, 1988).

The tolerance of oysters to withstand changes in salinity is enhanced by
their ability to close the shell valves when exposed to extreme conditions.
Valve movements and water transport were abnormal and growth inhibited
when the eastern oyster was exposed to low saline conditions (0 to 5 ppt)
(Loosanoff, 1953). Galtsoff (1964) observed that the oyster responded to low
salinity by partial or complete closure of the valves and slowing or cessation
of water current through gills. Exposure to an abrupt reduction from 27 ppt to
20, 15, 10, and 5 ppt resulted in decrease in pumping rate of 24, 89, 91, and
99.6% respectively for 6 hrs after transfer. Thereafter normal activity resumed
and there was no long-term effect on pumping rate.

Turbidity

Turbidity is another important ecological factor which has significant influence
on the tropical oyster beds (Yavari, 1994). Even if the productivity of the oyster
bed is high, the food cannot be filtered by the oyster in turbid condition. High
turbidity has been found to reduce the feeding rates, reduce the growth and
even lead to mortality in C.madrasensis beds along the east coast (Rao et al .,
1996). Continued occurrence of turbid waters for more than a week has been
found to affect the oyster spat more than the adult oysters. Along the west coast,
the growth and survival of C.madrasensis populations are adversely affected
by high silt load in the habitat during the monsoon period. High turbidity and
low salinity affect the oyster population along the west coast (Purushan et al. ,

Oyster Biology and Culture in India

1983, Rao et al., 1996), though quantitative estimates of mortality have not
been mentioned. Loosanoff ( 1 962) observed an average reduction of 57 to 94%
in the pumping rate of C.virginica in concentrations of 100 to 400 mg/1 of silt
and no pumping at all at higher concentrations. Suspended particles reduce
oyster gill functions and metabolic efficiency by increasing pseudofaeces
production. Oysters exposed to sediments have decreased growth and
reproductive efficiency, while mortality and disease susceptibility also increase
(Heral et al ., 1983). Hsia (1950) observed that in very turbid waters when the
silt was allowed to settle on the oysters, there was an immediate cessation of
shell movements for 16 to 19 hrs. The oysters subsequently attempted to
reopen the valves in an effort to remove the silt. If the silt deposits remained for
more than 3 days, mortality of oysters was observed. Siltation also reduces the
quality and quantity of suitable habitat for oyster ‘spat’ settlement (Keck et al.,
1973; Bahr, 1976; Mackenzie, 1983; 1989).

Food availability

Food availability is another important ecological factor which affects the
oyster population. Rao and Nayar (1956) have suggested that food availability
is probably the most important factor affecting the growth of C.madrasensis
in Adayar estuary. Chlorophyll-a concentration can be taken as a suitable
indicator of available food for oysters. For the Indian oyster C .madrasensis,
diatoms have been identified as the major food component. Yavari (1994) has
experimentally proved that chlorophyll -<2 and turbidity are critical parameters
which affect the growth of C.madrasensis. Apart from growth, favourable
phytoplankton blooms have been observed to induce spawning in C. gigas in
Spain (Ruiz et al., 1992).

Though very little is known about the optimum density and species
composition of the oyster’s plankton food source, some studies have indicated
that phytoplankton density influences the growth rate. In C.rhizophorae,
Wright et al. ( 1 990) found that when the phytoplankton density was 56.9 ± 1 5 .2
cells/ml the growth was 0.10 mm/day, while it was 0.58 mm/day in an area
where phytoplankton density was 178.9±100.9 cells/ml. Brown and Hartwick
(1988) have estimated 12 g chl-a/ml as the optimum level of food availability
for C. gigas. In the Ashtamudi Lake, where dense beds of C .madrasensis and
Saccostrea cucullata are seen, the average number of phytoplankton cells has
been found to be 255±155 cells/ml. Species belonging to 6 genera of
Cyanophycea, 19 genera of Bacillariophyceae, 8 genera of Chlorophyceae, 2
genera of Dinophyceae, 2 genera of Euglenaceae and 1 genus of Rhodophyceae
were found to occur in different densities in the oyster beds (Kripa, 1998).

The annual variations in pH in the oyster beds at Tuticorin were observed as
7.99 and 8.39 (Yavari, 1994) and 7.75 and 8.22 at Ashtamudi Lake (Kripa,

Oyster Resources, Distribution and Ecology

1998). Mortalities due to variation in pH have not been reported from Indian
waters. Studies conducted by Loosanoff and Tommers (1948) have shown that
pH affects the pumping rate of oysters. Oysters kept in waters of 4.25 pH
pump only 10 % as much water as control animals at 7.75 pH, even though the
oysters kept the valves open for about 75% of time.

The influence of biotic factors on oysters is given in detail in Chapter 3.

OYSTER REEF

Oysters occur as single oysters or in groups or may be scattered across dense
beds of accumulated shell, mud and sand (Winslow, 1882; Galtsoff, 1964;
Bahr and Lanier, 1981; Dame, 1996). Oyster settlement in an ecosystem is not
accidental (Keck et al ., 1973) and it is related to current speed, bottom
roughness (Wildish and Kristmanson, 1979) and hydrology (Hedgpeth, 1953).
The ability of oysters to cement to other oysters has lead to the formation of
oyster reefs. An oyster reef is an aggregation of live oysters and empty shells
occupying the bottom of an estuary (Galtsoff, 1964). The term is used
interchangeably with oyster bottoms, oyster beds, oyster banks, oyster rocks
and oyster grounds (De Alteris, 1988).

Oyster reefs are formed by continuous settlement, growth and death of
oysters in the same location over a period of time. The physical dimensions
and their structural variation or growth of the oyster reefs in the temperate
countries have been studied in detail. Bahr (1976) indicated that the development
of intertidal reefs of Georgia was an extremely slow process. De Alteris
(1988) has calculated that one oyster bed in the James River accrete vertically
at a rate of 0.5 m 100 yr-1.

Some of the oyster reefs in Chesapeake Bay are extensive. Me Comick-
Ray (1998) observed that in Chesapeake Bay, the widest reef was 2.3 km, the
longest 8.3 km, and largest 7 km2. The length of oyster reefs in India have not
been studied in detail. However, it has been observed that in certain estuaries
of east coast like Chunnambaru estuary, the oyster beds may extend to 750 m
in length and 60 to 200 m in width. Occurrence of multi- tier dense and
massive oyster heaps has been observed in Gadilam estuary, Vellar estuary,
Ennore estuary, Peddapatnam Revu creek, and Korapuzha estuary (Rao et al.,
1996). In some oyster beds, along with the live oysters, dead oyster shells are
present. In the Athankarai estuary, Sarvesan et al. (1988) have observed that
in some patches the live oysters form only 3 1 to 42% of the oyster population.
In Pulicat Lake, the oyster beds have both live and dead oysters, the former
contributing to 36.2-76.4% of the total oyster density (Thangavelu and
Sanjeevarj, 1988a). In Mudasudai- Chinnavaykal area extensive oyster beds
are seen in which live oysters formed 30%.

Oyster reefs are important components of the ecosystem. The benthic
structure caused by the horizontal and vertical expansion of oyster beds
influences the particle transport, biological organization, nutrient trapping and

Oyster Biology and Culture in India

sedimentation in the estuaries and coastal region (Me Cornick- Ray, 1998). The
functional and structural role of oysters in the ecosystem has not been very
well understood. Me Cornick- Ray (1998) has related the size of oysters
during different time frames to size of sedimentary particles as in Wentworth
scale (Ritter, 1986). The fertilized oyster egg which is 40-50 p m (Galtsoff,
1964) has the size of a clayey-silt particle, the veliger 200-300 p m, is equal
to the size of very fine sand particle initially and later develops to the size of
a fine sand particle (248-400 p m) (Carriker, 1996). After settlement, it passes
through the sizes of coarse sand (1000 p m), very coarse sand (2000 p m) to
reach the size of gravel at 90-150 mm. At this stage the oysters may be
harvested, but in certain unexploited beds the oysters continue to grow and
reach 260-350mm (Galtsoff, 1964; Haven et al, 1978; Stanley and Sellers,
1986; Ritter, 1986), which is equivalent to the size of a boulder.

Oyster reefs and their significance in the ecosystem have been the subject
of study in many parts of the world. It is now well documented that they
provide the following ecosystem services (Coen et al., 1997)

• Filter the water and curtail excessive turbidity and occurrence of
phytoplankton bloom.

• Help in benthic-pelagic coupling.

• Create feeding habitats for juvenile and adult mobile species.

• Provide substrata for sessile species (epifauna) and

• Provide nesting habitat.

Oyster reefs are considered as Essential Fish Habitat (EFH). They provide
habitat for ecologically, commercially and recreationally important finfish and
shellfish species (Coen et al., 1999). Oyster bed is a typical example of
‘biocoenosis’ or a social community of living beings, a massing of individuals
with ideal conditions governing their existence (Mobius, 1883) The shells of
oysters are natural abodes of many plants and sedentary animals which attach
to the shell surface (foulers) or bore through it (borers) to provide themselves
a well protected residence. Apart from these there are parasites which harm
the oysters while some others live within the dead oyster shells purely for
shelter. It has been observed that these reefs attract and sustain fishes of many
trophic levels (Harding and Mann, 1999).

In Pianktank River in Virginia, recreationally and commercially valuable
piscivorous finfishes including striped bass ( Morone saxatilis), bluefish
(Pomatomus salathrix) and weakfish ( Cynoscion regalis ) have been found to
be an integral component of trophic networks that depend on oyster reefs
(Harding and Mann, 1999). Further, Harding and Mann (1999) have observed
32 finfish species representing 26 families on or near the oyster reef in 1996-
1997. These pelagic fishes use oyster reefs as both feeding and breeding
ground.

The population structure and associated fauna in the oyster beds in the
Indian coast has shown seasonal variation largely dependent on the salinity of

Oyster Resources, Distribution and Ecology

the environment and the submergence time.The major variations seen in the
intertidal and subtidal oyster beds are given in Table 7.

The oyster beds in India have a wide variety of foulers, borers and other
fauna and flora. Barnacles, chiefly of the genus Balanus are probably the most
ubiquitous of all the fouling organisms. Balanus amphitrite is the main species
recorded followed by B.tintinnabulum, and Cathamalus stellata. Another
dominant fouler is the calcarean polychaete worm Hydroides sp. During the
monsoon season, these two foulers suffer mortality and several seaweeds and
bivalves succeed them. Seaweeds like Chaetomorpha, Ulva, Enteromorpha,
Gracilaria, Cladophora and Gelediella are associated with the oyster
population along the Indian coast (Rao and Sundaram, 1972; Muthiah et al.,
1987; Sundaram, 1988; Kripa, 1998). Bivalves like Modiolus striatula,
M.undulata, M.metacalfi, Anomia sp and Perna virdis are dominant in the
estuarine region. (Details about foulers, borers and predators of oysters are
given in Chapter 4)

Table 7. Variations in the oyster population structure observed in the marine intertidal,
estuarine intertidal and estuarine subtidal beds in Ashtamudi Lake

Marine intertidal

Estuarine intertidal

Estuarine subtidal

Oyster population
dominated by S.cucullata
forming 81 .7% of the
population.

C. madrasensis and

S. cucullata
(15 to 19%)

Oyster population
dominated by C.
madrasensis (>95%),
mostly live oysters.

Nature of oyster bed is
more like a reef;
approximately one
meter thick with dead
oyster shells forming

40 to 50 % of the
population. Live shells
only on the surface
of the reefs.

Thickness of oyster
bed less than half a
meter ; dead oyster
shells only 5-10% of
the population

Oysters occur as clumps
formed by the attachment
of three to four shells;
occurrence of dead
oyster shells negligible.

Barnacles are the main
epifauna throughout
the year.

Fouling by barnacles
low, seasonal variation
in associated fauna
such as calcareous
polychaetes, Modiolus sp.

Bivalves such as venerid
clams and mussels are
the main associated fauna.

Presence of seaweed low

Different types of sea¬
weeds are attached to
the oysters during late
monsoon and post
monsoon period.

Presence of seaweed low.

Polydora infestation low;
boring by sponges high.

Polydora infestation and
boring by sponge
moderate.

Polydora infestation high,
boring by sponge moderate
to low.

Oyster Biology and Culture in India

In Ashtamudi Lake, the shell surfaces and the cavities created by empty
dead shells have gastropod and fish egg cases. Juveniles of crustaceans and
finfishes are found to use the oyster beds as shelter, while several finfishes
frequently visit the sites for feeding on the foulers encrusting the oyster shells.
In the subtidal regions, oysters were associated with venerid clams like
Meretrix casta and Paphia malabarica. The empty clam shells are used by the
oysters for settlement (Kripa, 1998). In Pulicat Lake, Marphysa gravelyi ,
Eunice sp, Polynoe sp, Gammarus, polychaete larvae, amphipods, isopods
such as Sphaeoma sp, Lignio sp, Cirolina sp, nematodes, crabs and shrimps
are associated with the oyster beds (Thangavelu and Sanjeevaraj, 1988b). In
the oyster beds in Maharashtra, Sundaram (1988) has observed snails like
Planaxis sulcatus, Nerita spp, Certhium sp, and Cellana radiata, polychates,
small crabs, anemones and sponges. To the same site, the mud skipper
Boleophthalmus sp. and Therapon sp. are found to be occasional visitors.

Severe damages to the oyster reef by human activities such as intense
fishing, construction works and environmental degradation by chemical
pollution have been observed. Environmentalists, research and government
agencies are therefore taking several steps to revive these beds and restore
their species richness. Restoration of oyster habitats is now considered as an
important part of estuarine ecosystem management. In 1997 in Choptank and
Patuxent rivers in Maryland, fossil oyster shells were deposited at five sites in
a configuration of 2.5 acre flat areas and on mounds of 3 to 4 m height. Some
of these areas were planted with hatchery reared spat ( 1 million/ acre) while
the rest were left unplanted (Koles and Paynter, 1999). The planted spat
showed vigorous growth rate and spat settlement was noted on the unplanted
mounds.

In India, in certain regions like the Ennore estuary, heavy fishing of oyster
shells is prevalent. However, the damage caused by such fishing activities has
not been studied. Similarly the role of oyster reefs in the estuarine ecosystem
has not been investigated. Their significance as an essential fish habitat
serving the resident fauna and transient species remains to be critically studied.

QUESTIONS

1 . What are the major oyster species in India? Write on their distribution and

abundance?

2. Describe oyster reef/bed and associated fauna and flora.

Chapter 3

Biology

DURING the past one and half century, considerable research has been
done to understand the biology of oysters and refine the farming
techniques. The biological and physiological processes of oysters especially
the feeding mechanisms are better understood with the application of
microcinematographic techniques. Oysters live in an environment, which has
wide seasonal fluctuation, and efforts were made to apply the concepts of
physiological energetic in an environmentally realistic context. During the
past five decades, research has also targeted to identify the causative factors
responsible for mass mortalities of oysters which had lead to virtual destruction
of highly productive oyster beds.

In India, molluscan researchers were intrigued by the changes taking
place in the natural oyster beds and several studies have been conducted on the
biology. In this Chapter, the anatomy of oyster is described followed by a brief
summary of available information on the biology of Indian oysters.

External Morphology of Shell

The structure of the oyster shell has been described by several workers
(Baughman, 1947; Galtsoff, 1964; Stenzel, 1971; Breish and Kennedy, 1980).
Detailed studies about the microstructure, biochemistry and formation and
mineralization of shell have also been made (Wilbur, 1976; Carriker et cil.,
1982; Wilbur and Saleuddin, 1983; Watabe, 1984, 1988; Simkiss and Wilbur,
1989; Crenshaw, 1990; Carriker, 1996). A general description of the external
morphology and the oyster shell is given below.

The narrow end or apex of the shell is called the umbo or the beak and this
represents the oldest part of the shell. The soft body of the oyster is enclosed
within two shells, a larger lower left valve and an upper smaller right valve.
The left valve is usually cup shaped and cemented to the substratum. Juvenile
oysters attach their left valve to the substrate using fibrous organic matter
secreted from the foot (Cranfield, 1975). As they grow they begin to cement
themselves onto rocks or other hard surfaces using a part of the surface of their
lower left valve. The upper right valve is never involved in cementation under
natural condition. The thickness and strength of the shell valves are highly
variable and those grown under unfavorable condition are often thin and
fragile.

Oyster Biology and Culture in India

Shell morphology

The shell morphology of the oyster is extremely variable. Nature of the
bottom, salinity, temperature, current velocity, turbidity, direct sunlight, calcium
concentration and chemical pollution are some factors suspected to be involved
in the modification or changes in the shell morphology of oyster (Galtsoff,
1964; Carriker, 1996). The shape of oyster is determined by the contours of
substratum in which it grows and this phenomenon is called xenomorphism.

It has been observed that the oysters assume the following shapes when
grown on different substrata.

• Smooth and elongated when grown individually on soft substratum.

• Corrugated and circular shell with lower valve deep when grown on
hard bottom such as gravel.

• Irregular shape when grown with oysters.

• Circular/elongated with reduced cupped nature when grown fixed to
a firm substratum.

The highest commercial grade oysters come from areas where the bottom
is firm and non-shifting.

Biochemical composition of shell

The shell is composed of three layers: an outer thin periostracum, central thick
chalky layer and inner nacreous layer which is often thin, shiny, lustrous and
hard.

Calcium carbonate embedded in a protein mass is the main component of
the shell. The periostracum is almost all protein. Calcium carbonate constitutes
more than 95% by weight of the shell of Crassostrea virginica (Galtsoff,
1964). The conchiolin of the oyster shell is rich in aminoacids (Table 8). Apart
from this the shell is composed of a variety of minerals (Tables 9-11). Carriker
et al., (1991) conducted a study with proton induced X-ray emissions on the
distribution and concentration of 15 chemical elements (sodium to strontium
in the periodic chart of elements) of the shell of rapidly growing C.virginica.
Concentration of elements was calculated as percent by weight of the total 1 5
elements analysed. Concentration of calcium ranged between 908 ppt to 981
ppt. Titanium, chromium, manganese, iron, copper, zinc and bromine varied
from 0.01 to 4.78 ppt; sodium, magnesium, aluminium, silicon, sulphur,
chlorine and strontium ranged from less than 0.50 to 31.41 ppt. (for more
details, see also Carriker, 1996).The central layer and nacre have different
crystalline structures giving different appearances and texture. The oyster
larval shell which is ‘D’ shaped is termed Prodissoconch I and as it grows it
is termed Prodissoconch II. The adult calcareous shell formed after settlement
is termed Dissoconch.

On the inner side of the shell valve is the adductor muscle scar which is
the place of attachment of the adductor muscle. This muscle scar is the most
conspicuous area of the oyster shell and may be highly pigmented, light or

Biology

Table 8. Amino acids from the conchiolin of two species of oysters in parts of 100 parts
of protein

Amino acids

Crassostrea angulata

Ostrea edulis

Arginine

0.45

2.90

Histidine

0.65

Lysine

3.55

4.30

Glycine

15.70

Leucine

0.51

Tryptophane

0.48

Tyrosine

3.27

3.05

Valine

0.95

Cystine

0.98

Methionine

1.77

1.62

Source: Roche and Lafon (1951)

Table 9. Chemical composition of oyster shells in percent of shell weight

Constituents

Range

Constituents

Range

0.043 - 0.045

NEG-0.0009

38.78 - 38.81

0.0034-0.0035

NEG- 0.0025

57.19

0.09-0.11

0.183 - 0.189

0.196

0.009

P205

0.073-0.075

Organic matter1

1.41-1.51

Si02

0.570 -0.580

Water2

0.27-0.28

^oss above 1 10°C. Ignited; 2Loss to 100°C

NEG-Negligible

Source: Hunter and Harrison (1928)

Table 10. Chemical composition of C.virginica dredged from Galveston Bay

Constituent

Concentration Constituent

(%)

Concentration

(ppm)

Calcium (CaO)

54.6

Organic Carbon as CH4 400

Carbon (C02)

43.5

Chlorine (Cl)

340

Sodium (Na20)

0.32

Aluminium (Al)

200

Magnesium (MgO)

0.33

Iron (Fe)

180

Sulfur (S02)

0.16

Phosphorus (P)

116

Silicon (Si02)

0.16

Manganese (Mn)

110

Strontium (SrO)

0.12

Fluorine (F)

Moisture (H20)

0.58

Potassium (K)

Total

99.8%

Titanium (Ti)

Boron (B)

Copper (Cu)

Zinc (Zn)

Bromine (Br)

Iodine (1)

0.5

Source: Smith and Wright (1962)

Oyster Biology and Culture in India

Table 11. The percentage of calcium and strontium in shells of oysters

Species

Calcium

Strontium

Carbon

dioxide

Organic

matter

Atom ratio

Sr/Ca
x 1,000

O.lurida

C. virginica
C.gigas

38.6

33.7-37.8

34.6-36.2

0.085

0.92-0.107

0.097-0.100

42.5

41.8-42.4

32.6-42.5

1.68

2.16-2.34

1.33-1.71

1.01

1.25- 1.29

1.26- 1.28

even absent. A narrow band of dark elastic material called the ligament which
has a purely mechanical function is situated along the edge of the hinge
between the two valves. It helps the adductor muscle to open and close the two
shell valves. The anterior margin of the shell is the hinge side and the posterior
margin is the opposite.

Shell dimensions

The commonly used terminologies to describe the dimension of oysters are
length, width and thickness (Quayle and Newkirk, 1989) (Fig. 6). The axis or
the orientation of shell and the corresponding terminologies used are given in
Table 12

Table 12. The terminologies used to describe the shell dimensions

Axis/orientation

Dimension

Common

usage

Anterio-posterior axis

Height

Length

Maximal distance between ventral and dorsal
margin parallel to hinge axis (dorsoventral axis)

Length

Width

Maximum distance between outer surface of
closed valves measured at right angles to the
plane of closure of valves

Width / Depth

Thickness

ANATOMY

Detailed description of anatomical features of oysters is available from the
works of Moore (1898), Brooks (1905), Churchill (1920), Galtsoff (1964) and
Eble and Scro (1996). The salient features of the different systems are given
below.

Mantle

The body of the oyster (except the adductor muscle area) is covered by a soft
fleshy fold of tissue called the mantle or the pallium. The left and right folds
of mantle join together at the dorsal edge where it forms a cap and covers the
mouth. The mantle edges are also fused at the posterior margin (in the region
of the cloacal chamber). The remaining edges of the mantle are free. The large
cavity bounded by the mantle lobes is the pallial cavity or mantle cavity which

Biology

Fig. 6. Diagram showing the shell dimensions of oyster

is usually filled with water. This seawater which contains various products of
oyster’s metabolism and mucous is called ‘shell liquor’ and it helps the oyster
to survive in the intertidal zone. For oysters in the sub-tidal region, the shell
liquor helps to tide over the unfavourable situation caused by floods or
temporary presence of toxic or irritating substance in water which forces the
oyster to keep its shell closed. The mantle is always in contact with the valves,
but is not attached to them.

The mantle cavity contains the palps and gills on one side and the rectum
on the other. The rectum opens dorsally to a special portion of the dorsal
pallial cavity known as the cloacal chamber. The right lobe of the mantle is
separated from the visceral mass to form the promyal chamber (Fig. 7); the left
lobe is fused to the visceral mass (Eble and Scro, 1996). The pallial cavity is
subdivided into two chambers. The cavity formed by the fusion of the mantle
dorsally with the visceral mass and ventrally with the bases of the gills is
known as epibranchial chamber. It continues posteriorly as the cloacal chamber.
The large cavity containing the gills and bounded by the two mantle lobes is
the hypobranchial chamber.

The border of the mantle is divided into three lobes - the outer or shell
lobe is narrow and lies in contact with the margin of the shell. The middle lobe

Oyster Biology and Culture in India

Fig. 7. Promyal chamber viewed from the posterior side of an oyster

1 . Promyal chamber 2. Rectum 3. Left valve 4. Anus 5. Adductor muscle
6. Cloacal chamber 7. Mantle 8. Hypobranchial chamber 9. Right valve

bears sensory tentacles and is separated from the shell lobe by a deep cleft, the
periostracal groove (Galtsoff, 1964; Eble and Scro, 1996). The inner lobe is
called the pallial curtain (Nelson 1938). It bears long, thick tentacles. By
interlocking the long tentacles of both sides of the pallial curtain, the entrance
to the mantle cavity can be sealed. Even if the valves are open, no exchange
of water can take place where the pallial curtain is sealed. Instead of completely
closing the pallial curtain, the oyster can selectevely open certain regions. By
contracting the adducter muscle, the oyster can eject strong jets of water from
the mantle cavity. A ligamental ridge, which secretes ligament, is also situated
in dorsal region of the mantle. The main organs of Crassostrea sp. as seen
after removal of right valve is given in Fig. 8.

The main functions of the mantle are:

• Formation of shell and secretion of ligament.

• Reception of sensory stimuli and conveying them to the nervous
system.

• Shedding and dispersal of eggs and sperm.

• Respiration.

• Storing of reserve material like glycogen and lipids.

• Excretion by discharging blood cells with waste material.

Muscular system

The single adductor muscle is the main muscular part of oysters and it is
located about two thirds of the distance from umbo or nearer to umbo. It’s

Biology

Fig. 8. Organs of Crassostrea sp. after removal of right valve 1 .Outer labial palp 2.
Passage to mouth 3. Oesophagus 4. Stomach 5. Ascending intestine 6.
Descending intestine 7. Style sac - midgut 8. Liver diverticula (digestive
gland) 9. Rectum 1 0. Anus 1 1 . Cloacal chamber 1 2. Pericardial chamber 1 3.
Heart 14. Outer gill 15. Adductor muscle 16. Left mantle 17. Sensory tent¬
acle (papilla) 18. Anterior side 19. Posterior side 20. Dorsal 21. Ventral side.

major function is to control the opening and closing of the valves. In most
oysters, it accounts for 20 to 40 % of the total weight of the tissue. Adductor
muscles are composed of long, narrow uninucleate muscle cells called fibers
(Morrison, 1996). The adductor muscle consists of two sections, a large
anterior beige coloured area called the ‘quick muscle’ which is responsible for
the main opening and closure of the valves and a smaller white coloured
section called the “catch” muscle which can hold the valves in a set position
for long periods with little expenditure of energy. The adductor muscle works
continuously against the pressure of the hinge ligament which pushes to open
the valves. The power of the adductor muscle varies with the size and
condition of the oyster. A pull of over 9 kg is required to open the shell of a
good American oyster of 7.5 to 10 cm size.

Oyster Biology and Culture in India

The mantle, including the lobes is very contractile and can be withdrawn
inside the shell (Galtsoff, 1964). In the mantle the radial muscles extend from
the visceral mass of the mantle edge. They are also present in the lobes. A
layer of circular muscle is present near the pallial surface at the base of the
lobes. There is also a layer of small muscle fibres just below the epithelial
surface (Carriker, 1996).

Respiratory system

The gills perform several important functions and play a major role in
respiration, to which the mantle contributes a minor share. They create water
currents, filter the water, collect food particles, and move them to labial palps.
They also serve for dispersal of gametes and incubate the fertilized eggs in
larviparous oysters. The gills consist of four folds (demibranchs) of tissue
suspended from the visceral mass and occupy much of the ventral and ventro-
posterior portions of the mantle cavity (Fig. 9). In cross section the gills have
the shape of four V’s, a double V on the right and another on the left side of
the oyster. Each V is known as a demibranch and each arm of the V is called
a lamella, with an inner descending lamella and an outer ascending lamella.
Thus two marginally folded lamellae constitute a demibranch and two joined
demibranchs form a gill. Each lamella is composed of vertical filaments which
in turn are clustered in vertical folds or plicae.

Each gill is attached to the body of the oyster at the open end of VV
known as gill base. The projected end of the VV is known as gill margin and
it projects into the mantle cavity (Galtsoff, 1964; Eble and Scro, 1996)

Fig. 9. Diagrammatic representation of the gills of Ostredae

Biology

The inner two demibranchs are joined together at the central axis of the
gills under the common efferent vein. The structuiral unit of a gill is a tubular
filament supportd by chitinous rods. The filament has laterofrontal and lateral
cilia (Fig. 10 ).The space in the central part of the filament is periodically filled
with blood as gill plates expand and contract. The cilia are of various sizes and
beating of the cilia aids in maintaining current which helps in gaseous exchange
for respiration. The mantle participates in respiration by providing direct
exchange of gases between surface of the oyster and the surrounding water.

In Crassostrea, the exhalent system is modified by the presence of promyal
chamber. The gills filter the water and collect food particles which are sorted
and separated from incoming current of water. The filtered water is passed out
through the area behind the adductor muscle and also through the promyal
chamber. The water current also helps in dispersing the gametes during
spawning.

Digestive system

The digestive system of oysters consists of a mouth, short oesophagus, stomach,
crystalline style sac, digestive diverticulam, midgut, rectum and anus. The
mouth is a compressed U- shaped opening between the two lips, the labial
palps (Fig. 8). The labial palps lie at the extreme anteroventral side of the body
just under the oral hood of the mantle. The broad bases are attached to the

Oyster Biology and Culture in India

visceral mass dorsally while the slightly curved margins extend posteriorly to
the point where they are in juxtaposition to the free edges of the gills. The
mouth is lined with a stratified, tall, ciliated columnar epithelium (Eble and
Scro, 1996) and opens into the oesophagus, which is a short funnel shaped
dorso-ventrally compressed tube.

The oesophagial epithelium has unicellular glands that contain acid and
neutral mucopolysaccharides (glycosaminoglycans) (Beninger et al., 1991;
Eble and Scro, 1996). The oesophagus enters the anterior chamber of the
stomach at the junction of the latter with the caecum (Shaw and Battle, 1957).

The stomach is a large sac-like organ that is divided into anterior and
posterior chambers. The anterior chamber gives rise to anterior and posterior
caeca and two primary ducts that lead to the digestive diverticula. The posterior
chamber of the stomach is separated from the anterior chamber by a broad
ridge that projects into the lumen from the mid ventral wall. It also has the
gastric shield, a plate-like, translucent structure embedded in the left ventral
wall. It consists of two main lobes joined by a narrow neck. Just posterior to
the gastric shield, the posterior stomach leads into an elongated outpouching
called the style sac-midgut (Eble and Scro, 1996). The style sac produces the
crystalline style and rotates it against the gastric shield releasing the contained
carbohydrates into the lumen of the posterior stomach. The midgut is separated
from the style sac by the greater and lesser typhlosoles (Shaw and Battle 1957;
Galtsoff, 1964). The next significant part of the digestive system is the
intestine consisting of ascending, median and descending portion. The ascending
limb of the intestine arises at the common posterior chamber of the style sac
and midgut. Near the anterior extremity of the visceral mass, the ascending
limb descends ventrally to form the median limb. The descending intestine
runs posteriorly in the ventral portion of the visceral mass, then crosses
obliquely to the left and runs along the dorsal margin of the pericardial sac
before opening into the rectum. The rectum runs dorsally over the adductor
muscle and ends in the anus that is located in the cloacal chamber.

Another important component of the digestive system is the digestive
gland. Three primary ducts leave the stomach, two from the anterior chamber
and one from the posterior chamber; they divide into many secondary ducts,
which in turn branch into the pretubular ducts. These lead directly to digestive
tubules.

Circulatory system

The circulatory system consists of heart, arteries, veins and open sinusus. The
heart is situated close to the adductor muscle on the anterior side. It is
suspended obliquely in the pericardial coelom. The pericardial coelom is a
thin walled chamber between the visceral mass and the adductor muscle. It
protects the heart. The systemic heart is three-chambered consisting of two
atria and a common ventricle.

Biology

The pear shaped ventricle is larger than the two auricles. Its walls are
formed by thick bundles of non-striated muscle fibers. The auricles are dark
coloured due to the presence of pigment cells in their walls. The degree of
pigmentation varies from light brown to almost black (Galtsoff, 1964). The
walls of the auricle are thinner and lighter than those of the ventricle. The
ventricle is separated from the atria by a constriction, the atrioventricular
junction (Eble, 1996).

Lack of continuity between the arteries and veins due to the presence of
sinuses is the characteristic feature of the open circulatory system of bivalves.
The spaces which function as capillaries have no distinct walls, are of irregular
shape and appear as slits in the tissue (Galtsoff, 1964). Two large arteries, the
anterior and posterior aorta emerge from the posterio-dorsal side of the
ventricle. The arterial system consisting of several arteries like the pericardial,
visceral, rectal, circumpallial, subligamental, cephalic and labial arterie which
supply blood to different parts of the oyster. The venous system comprises the
sinuses, afferent and efferent veins and small vessels of the gills. Most oysters
also have an accessory heart which is a paired tubular structure fixed to the
mantle near the cloacal chamber. They project into this chamber. This helps in
moving the blood through the mantle. Oscillation of the blood in the mantle
is the primary function of the accessory hearts.

The mantle and the gills are the two main organs for oxygen exchange
with the environment. Eble (1996) after giving a detailed account of the
arterial and venous systems has described the physiology of circulation.
According to Eble (1996) the systemic heart pumps haemolymph to the
visceral mass and adductor muscle. The haemolymph from various organs in
the visceral mass is collected by veins and delivered to the gills. Haemolymph
in the adductor muscle flows mainly into the gills, secondarily into the kidney.
Accesory hearts pump haemolymph from the kidney to the mantle.
Haemolymph circulates through gills before returning to the heart. Large
veins in the mantle collect haemolymph which is returned to the heart.

Excretory system

The kidney is a tubular gland that lies in a large haemolymph sinus called the
renal sinus. The anterior limbs of the kidney lie anterior to the heart, embedded
in Leydig cell connective tissue just under the mantle. The main part of the
kidney lies under the heart and adductor muscle, extending the entire width of
the animal (Eble and Scro, 1996).

The excretory system consists of nephridia situated on either side of the
visceral mass (Fig. 11). The nephridia are markedly asymmetrical, the right
being larger than the left. Each nephridium consists of a central portion, the
body with its short wide duct, and two limbs, an anterior and a posterior. The
body of the nephridium encloses a large lumen and communicates with the
nephridium of the other side through a transverse canal. Both the limbs of the

Oyster Biology and Culture in India

Fig. 1 1 . Excretory system of oyster. 1 . Anterior right limb of nephridium 2. Pericar¬
dium 3. Efferent vein 4. Renopericardial opening 5. Renoperi-cardial canal
6. Right nephridium 7. Renal duct 8. Reservoir 9. Renogonadial vestibule
10. Posterior right limb of vestibule 11. Visceral ganglion 12. Anterior left
limb of nephridium 13. Ventricle 14. Auricle 15. Inter-nephridial passage
1 6. Left nephridium 1 7. Adductor muscle 1 8. Posterior left limb of nephridium

nephridium are formed by numerous branching and twisted tubules lined with
excretory cells. Most of the posterior limb of the nephridium is occupied by
a wide vesicle or reservoir for storage of urine. A short renal duct leads from
the reservoir to the outside and opens into renogonadal vestibule through
which both reproductive and excretory products are discharged. In addition to
nephridia, pericardial glands, wandering amoebocytes and the mantle epithelium
also perform excretory function (Galtsoff,1964)

Eble and Scro (1996) have stated that in the eastern oyster, the pericardial
gland is reduced to mesothelial granular cells that line the pericardial coelom
and are also present as ‘brown cells’ associated with atria. The structure and
function of brown cells as well as renal filtration and physiology are described

Biology

by Eble (1996). The wandering phagocytes are found throughout the tissues
of the visceral mass and gills. They accumulate on the surface of the body by
diapedesis and are discarded. Mucus or goblet cells on the surface epithelium
also help in excretion.

Nervous system

Oysters do not have a major control centre like the brain. The nervous system
is simple, comprising of two main ganglia, the visceral and the cerebral
ganglia (Galtsoff, 1964). They are joined by the cerebro- visceral connectives
(Fig. 12). The U-shaped cerebral commissure goes around the oesophagus and
the circumpallial nerve extends along the mantle’s edge. Several nerves
originate from the ganglion and extend to different parts of the body. The

Fig. 12. Nervous system of Crassostrea sp. seen from right side. 1 . Adductor muscle
2. Adductor muscle nerve 3. Visceral ganglion 4. Branchial nerve 5. Cere¬
bral ganglion 6. Lateral pallial nerve 7. Gills 8. Rectum.

Oyster Biology and Culture in India

pedal ganglion is absent. The tentacles along the edge of the mantle and the
pallial organ inside the cloaca are the only sense organs of the oyster. The
tentacles are highly sensitive to illumination, temperature and chemical changes
of the surrounding water. The function of the pallial organ is not well understood.
Eyes are present in fully grown larvae, but absent in adult oysters.

Reproductive system

The sexes are generally separate (heterosexual) though hermaphroditism has
been recorded. The reproductive organ is the gonad situated in the visceral
mass between the digestive gland and the mantle. It originates at the region of
the oesophagus, extending the length of the visceral mass to the pericardial
area where it bifurcates into a dorsal lobe that extends towards the rectum and
a ventral lobe extends to the posterior extension of the visceral mass. During
the resting phase the gonad cannot be distinguished grossly from the surrounding
vesicular connective tissue. The outline of the gonad is indistinct. When fully
developed the gonad measures several millimeters thick and has many branching
channels, the gonoducts which are clearly visible on the surface (Fig. 1 3). The
sex cells are discharged through the gonoducts into the urinogenital grove

Gill

Gonoducts

Mantle

-Shell

Adductor muscle

Genital opening

Fig. 13. Ripe gonad of oyster

Biology

(vestibule) and from there they are passed to the outside through the epibranchial
chamber. The sex of the oyster cannot be differentiated externally.

FOOD AND FEEDING HABITS

Oysters are filter feeders capable of filtering and utilizing the phytoplankton
and organic detritus suspended in the water. The food particles are moved
mainly by the ciliary action of the gills. With the application of new
microcinematographic techniques it has been possible to understand the various
feeding structures of bivalves in vivo (Newell and Langdon, 1996). Ward et al.
(1994), observed previously undetected tract along the most anterior margin
of the demibranch that serves to carry excess particles away from the basal
gill-palp junction. The food particles in the incurrent water pass through the
gills and get entrapped, bound in mucus and are directed towards the labial
palps. The labial palps play an important role in sorting and selecting the food.
They either direct the particles towards the mouth or reject it as pseudofaeces.
Bernard (1974) has stated that the ciliated ridges on the palps reject the entire
mucous - particle load if the size of particle is large. Considerable discrepancies
exist in the results of studies on retention efficiency and particle size. Haven
and Morales-Alamo (1970) and Palmer and Williams (1980) reported that
C.virginica can retain particles in between 3 to 6 pm size range with efficiencies
as high as for particles larger than 6 pm. Conversely, Riisgard (1988) reported
that C.virginica can retain particles smaller than 6 pm with lower efficiency
than that reported for many other bivalve species. The mucus enmeshed
particles which enter the oesophagus mix with enzymes released by the
crystalline style and extra- cellular digestion of starch takes place. By a
combination of ciliary pathway in the sorting pouches and in the stomach
itself, small and partially digested particles are carried to the tubules of the
digestive gland where intracellular digestion of fat and protein takes place
(Quayle and Newkirk, 1989).

Digestive tubules of C. madrasensis are found to be monophasic, i.e. at a
particular tidal phase almost all the tubules have a homogenous structure.
During high tide these tubules are used for digestive and absorptive phases
while during low tide the disintegrating and reformative phases are dominant
(Hameed and Paul Pandian, 1987). Histological study of the digestive tubules
of intertidal and subtidal C.virginica showed that the intertidal C.virginica
responds to tidal cycles by losing or reconstituting the crystalline style
concomitant with changes in tubule morphology. In contrast, in subtidal
oysters the digestive tubules are not affected by normal tidal cycles, supporting
the contention that they are continuous feeders (Winstead, 1997).

Yonge (1926) reported that protein and fat digestion occurred only
intracellularly within the wandering phagocytes, and the starch was digested
only extracellularly by the action of thyliamylase. Phagocytosis mainly occurs
in the digestive diverticula. The oyster is also capable of absorbing dissolved

Oyster Biology and Culture in India

organic matter in the water through the surface of gills, palps and mantle (Owen,
1 974). Apart from this, blood cells capable of engulfing the food also ingest and
digest individual particles of food.The granular haemocytes in the alimentary
canal of oysters have wide range of digestive enzymes including amylases,
lipases, esterases and proteases (Yonge, 1926;Takatsuki 1934; Mathers, 1973).
Haemocytes containing digested material in the haemocoel surrounding the
digestive tubules have also been observed (Yonge, 1 926; Morton, 1971). There
are important enzymes in the stomach which help in the digestion of starch and
glycogen. Digestive enzymes have been observed in the digestive diverticula
(Mathers, 1973; Onishi et al., 1985; Brock et al., 1986) and midgut (Mathers,
1973). He also observed different polymerases and oligomerases in the stomach
contents, stomach wall, style sac and style of oysters.

Several studies have been made on the gut microflora of oysters Cristispira
spp. A colourless gram negative spirochaete has been observed to live in the
matrix of the style of oysters (Dimitroff, 1926). These can be distinguished by
the presence of a ridge or crest-like structure called the ‘crista’ (Tall and
Nauman, 1981). Dimitroff (1926) has stated that a smaller spirillum, Spirillum
ostreae, may also be present in the style. It is believed that these contribute to
the style’s production of enzymes. However, Mayasich and Smucker (1987)
have inferred that the enzymes in the crystalline style of oysters are produced
endogeneously and that Cristispira spp. and the bacteria do not contribute
significantly to the production of enzymes. Crosby and Reid (1971) have
suggested that the gut microflora play a significant role in extracellular
digestion of cellulose, but they have not been able to determine the relative
importance of endogenous versus exogenous cellulases of bacterial origin.

The unwanted materials are directed by the caeca along a special path
called typhlosole, to the opening of the intestine, where these are compacted
into solid strings and are ejected out in the exhalent water current via the anus.
The faecal ribbons of the oysters contain many live cells-diatoms,
dinoflagellates, yeasts and others which are not digested by the gastric and
intestinal juices.

Filtration rates

The oysters, as mentioned earlier, are filter feeders and the water currents
produced by the ciliary action of the gills serve both respiratory and feeding
functions. Exogenous factors like water currents (Grizel et al., 1992), seston
concentration (Higgins, 1980a; 1980b), temperature, salinity (Rajesh et al,
2001) are some of the factors which influence the feeding processes of oysters.
The rate at which suspended food is filtered from the suspension is determined
by the pumping or the ventillation rate (rate at which water is transported
through the gills) and the retention efficiency (the efficiency with which
particles are retained by the gill) (Malcouf and Bricelj, 1989). The retention
efficiency is found to depend on the particle size and particle concentration.

Biology

It has been clearly observed that all the material retained is not utilized by
oysters and part of it is eliminated as pseudofaeces (Langdon and Newell,
1996). The combined production of pseudofaeces and faeces (material that is
ingested but cannot be absorbed or metabolically utilized) is referred to as
biodeposition rate.

The physiological measurements of filtration rate (FR), clearance rate
(CR), pumping rate (PR) and ingestion rate (IR) are generally used to study
the ecological energetics. The CR is defined as the volume of water filtered
completely free of particles per unit time. Pumping rate is the volume of water
flowing through the gills per unit time. When all the suspended particles are
removed by the gills with 100% retention efficiency, clearance rate is the same
as the pumping rate. The IR or feeding rate is defined as the number of algal
cells an organism consumes per unit time (Malcouf and Bricelj, 1989). Direct
measurements of pumping rates have posed several practical difficulties.
Hence indirect methods have been proposed and instead of pumping rates,
clearance rates have been determined (Iglesias et al., 1998). There are two
methods to measure the clearance rate.

a) Measurements in closed or static systems that are based on the rate of
depletion in particle concentration due to filtering activity. This method
is called Coughlan method. (Coughlan, 1969).

b) Measurements made in an open or flow through system. Here the
percentage of reduction in particle concentration that occurs in a water
mass when flowing through the chamber with one or more bivalves
inside is measured. Both these methods have been found to give
comparable results. When the particle concentration is high and the
oyster produces pseudofaeces, then the rate of particle rejection is
also measured. Then ingestion rate = filtration rate (FR) - rejection
rate (RR). The only way to measure rejection rate is by the direct
quantification of produced pseudofaeces, which can be easily
performed by quantitative collection followed by gravimetric
determination of collected matter (Iglesias et al. 1998). The FR and IR
are calculated using the following formulae (Ali, 1970; Walne, 1972).

log cone, t - log cone, t

The filtration rate, (F ml/hr) F = V x - - - x 60

log e t

Where V = volume (ml of algal solution used); cone. to = initial
concentration and cone. t] = algal concentration after time t.

c. - C2

Ingestion rate (I, cells/hr/animal) I = - x V x 60

Where C = initial algal concentration; C0 = final algal concentration after
time t; t = duration of the experiment in minutes, V = volume of water and n
= number of oysters.

Oyster Biology and Culture in India

The FR of C.madrasensis is influenced by the salinity. It was highest at
20 ppt salinity than at 10 and 32 ppt (Rajesh et al., 2001). The FR of
C.madrasensis of two different size groups 65-70 mm and 100-105 mm was
compared and FR of larger animals was found to be significantly (P<0.05)
higher. The FR of 65-70 mm and 100-105 mm was 15.509 1/hr/animal and
21.389 1/hr/h animal respectively in an algal cell concentration of 7.5 x 104
cells /ml at 20 ppt. During the last decade efforts have been made to apply the
concepts of physiological energetics of bivalves in an environmentally realistic
context (Navarro et al., 1991 ; Hawkins et al., 1996). Recently Hawkins et al.
(1998), have observed that bivalves are able to selectively enrich the organic
content of ingested matter relative to filtered matter, preferentially rejecting
inorganic matter prior to ingestion as pseudofaeces. In a natural system the
efficiency of selection varied positively with both the mass of seston filtered
per hour and organic content of filtered matter. Accordingly, when the food
available was high, the mass of seston filtered per hour was greatest and more
than 60% of the organic matter ingested per hour resulted from selective
processes.

REPRODUCTION

Reproduction in oysters is controlled by endogenous factors such as stored
nutrients and neuroendocrine compounds and by exogenous factors such as
salinity, temperature and pheromones (Stephen, 1980; Joseph and Joseph,
1988; Littlewood and Donovan, 1988; Mane and Nagabhushanam, 1988;
Thompson et al., 1996).

The seasonal changes in gonad development and the principal exogenous
factor which stimulate spawning in C.madrasensis have been studied (Hornell,
1910a; Panikkar and Aiyar, 1939; Paul 1942; Rao 1951, 1953, 1956; Rao
1974; Stephen 1980; Joseph and Madhyastha 1982; Rajapandian and Rajan
1983; Narasimham 1987; Joseph and Joseph 1988). Stephen (1980) and
Joseph and Joseph(1988) have investigated the changes in biochemical levels
of the adductor muscle, mantle and gonad with the gametogenic cycle of
C.madrasensis. Durve (1965) and Mane and Nagabushanam (1976, 1988)
have described the gametogenic cycle of C.gryphoides along the Maharashtra
coast. The annual reproductive cycle of S.cucullata has been studied by
Sukumar and Joseph (1988) and Kripa (1998).

In Crassostrea species the eggs produced by the female gonad and the
sperms by the male are discharged externally into the open environment where
fertilization takes place. During spawning, the sperm is discharged as a steady
stream in the exhalent water through the genital pores. The spawning in
female is slightly different; the exhalent opening of the mantle is closed, the
valves are kept open and most of the inhalent area except for small opening
in the posterior ventral region is also closed. The released eggs are collected
in the inhalant chamber as they cannot be discharged through the exhalent

Biology

chamber which is closed. The adductor muscle then contracts rapidly and the
cluster of eggs is forced out through the small opening along the mantle edge
curtain. The eggs are ejected about 30 to 60 cm away from the oyster thereby
ensuring the dispersal. Depending on the species, the maturity of the gonad
and the environmental conditons, the entire spawning may be completed at a
stretch within a short period or with short pauses or may extend for days or
week (Galtsoff, 1964; Quayle and Newkirk, 1989).

In oysters of the genus Ostrea the eggs are retained within the inhalant
chamber of female and the sperms from the adjacent spawning male enter the
female with the inhalant water current and fertilize the eggs. The fertilized
eggs are incubated in the chamber for 10 days and are released as half grown
larvae (Quayle and Newkirk, 1989) by the female.

Hermaphroditism

Oysters have no secondary sexual characters and their sex can be recognized
only during the reproductive periods by microscopic examination of gonads.
The oviparous species of oysters of the genus Crassostrea usually are not
functional hermaphrodites. Specimens in which functional eggs and sperms
are found together are rare (Galtsoff, 1964). In the viviparous Chilean oyster,
Triostrea chilensis of Northern New Zealand, simultaneous hermaphrodite
oysters have been reported (Jeffs et al., 1997). Hermaphroditism has been
noted in different populations of C. madrasensis along the east and west
coasts. Rao (1953, 1956) recorded hermaphroditism in C. madrasensis
throughout the year while Rajapandian and Rajan (1987) and Narasimham
(1987) noted hermaphroditism only in stray instances in spent and recovering
stages along the east coast. (Fig 14f)

Sex change

In C. madrasensis, young oysters of ‘O’ year group are functional males upto
78 mm size. In one year old and above (118.5 mm), 72% of the population
were females (Rajapandian and Rajan, 1987). In Ostrea the sex may alternate
once or several times within one breeding season depending on temperature
and food conditions. In general, the proportion of males and females remains
approximately equal in spite of these sex changes (Quayle and Newkirk,
1989).

Fecundity

The fecundity of the oysters of the genus Crassostrea is about 100 million
eggs (Quayle and Newkirk, 1989). The size of the ova when spawned is about
70 pm and the sperm head is about 3 pm. The eggs of C.madrasensis measure
48 - 60 pm in diameter. The fecundity of this species is 10 to 15 million eggs
(Rajapandian and Rajan, 1987).

Oyster Biology and Culture in India

Sexual maturity and Spawning season

Seasonal gonadal changes can be studied by gonadal smear or histological
preparations (Quayle and Newkirk, 1989). The gonadal changes can also be
evaluated by visual - observation. Gonadal smears are prepared by making a
small cut on the surface of the body of the oyster with a scalpel at a point half
way between the position of the mouth and the adductor muscle. The smear
taken should be examined immediately. Histological preparations provide
reliable assessment of the gametogenic state of the oysters. It is common to
divide the reproductive cycle of the oyster into 5 stages (Table. 13 and Figures
14 and 15)

Table 13. Distinguishing features of maturity stages of the oyster gonad

Stage

Condition of gonad

Indeterminate

Difficult, if not impossible, to determine sex, follicles absent.

Maturing

Beginning of gametogenesis with the appearance of follicles;
primary sex cells seen on the follicle walls.

Ripe

Follicles enlarged and gametes capable of fertilization and sperms
active.

Partially spent

Recently spawned with follicles partially collapsed, few mature
ova and sperm also present.

Spent

Completely spawned with follicles collapsed without ova or sperm.
This is followed by accumulation of Leydig tissue and back to
stage 1 or 2.

The development of gonad in an individual is a continuous process in each
follicle. It has been observed that the gonad forms about 30 to 40% of the total
body weight, exclusive of shell.

The males of C.madrasensis and Saccostrea cucullata attain maturity as
they reach a size of 12-14 mm and 18-22 mm respectively. The majority of
females of the former species mature at 24-26 mm and the latter at 20-22 mm
(Joseph and Joseph, 1988; Kripa, 1998). Along the Indian coast, it has been
observed that the majority of the oysters in a population reach maturity at the
same time and spawning is triggered through interactions between the oyster
and the environment resulting in synchronous spawning during the peak
spawning period. The spawning trigger for the Indian oysters has been attributed
mainly to variation in salinity (Homell, 1910a; Moses 1928; Paul, 1942; Rao,
1951; Durve, 1965; Stephen, 1980; Joseph and Madhyastha, 1982; Kripa,
1998). The spawning season and periodicity has been found to differ for the
Indian oysters (Table 14).

Along the east coast, at Madras Harbour, C.madrasensis has been reported
to have year round spawning, while north of this in Kakinada Bay the species
has a restricted spawning and does not spawn during July-December when the
salinity is low. Down south, at Tuticorin, two spawning periods have been

Biology

Fig. 14. Maturity stages of Crassostrea madrasensis a) Maturing female b) Ripe
female c) Partially spawned female d) Spent female e)lndeterminate stage
f) Hermaphrodites (after Rao, 1958)

observed. Along the Indian west coast, in Kerala, C. madrasensis spawns
during the post monsoon period (Nov -Dec) when the salinity and temperature
of the coastal waters increase. Minor spawning has been observed during the
summer months also. In Karnataka, the same species has a peak spawning

Oyster Biology and Culture in India

Fig. 15. Maturity stages of male Crassostrea madrasensis a) Maturing male b)
Ripe male c) Partially spawned male d) Spent male (after Rao,1956;
Narasimham, 1987)

period just during the premonsoon period (Apr-Jun) and another minor one
during postmonsoon. However, under low salinity and temperature during the
monsoon, the spawning activity is greatly reduced. Though the spawning
season of C. madrasensis along both the coasts has been found to vary, it can
be inferred that the spawning takes place when the salinity of the ambient
water is between 20 and 30 ppt. Generally spawning occurs when the salinity
increases. Homell (1910a) was the first to draw attention to the relationship
between sexual activity of oysters and salinity. This pronounced relationship
prompted Stephen (1980) to term this relationship as ‘Homel’s Rule’. Apart
from salinity variation, diurnal variations in temperature have also been
suggested as favorable for spawning in C. madrasensis along the east coast
(Rajapandian and Rajan, 1983; 1987). Spawning has also been related to a
combination of rising water temperature and salinities (Narasimham, 1987).

Biology

Table 14. Spawning season of oysters along the Indian coast

Location

Peak

spawning

period

Environmental factors
triggering spawning

Reference

C.madrasensis

Kakinada Bay

Jan - June

Rising temperature
and salinity

Narasimham(1987)

Madras harbour

Throughout
the year

Variation in salinity

Paul (1942)

Adayar estuary

Oct- Dec,
Mar - Apr

Variation in salinity

Rao (1951), Rao and
Nayar ( 1956)

Tuticorin

Jul-Sep,

Diurnal variation in

Rajapandian and

Feb- Apr

temperature

Rajan (1983)

Mulki estuary

Apr- Jun,
Nov

Variation in salinity

Stephen (1980)

Joseph and
Madhyastha (1982),
Joseph and Joseph
(1988)

Ashtamudi

Nov-Dec

Rising temperature
and salinity

Velayudhan et al.
(1995)

C.gryphoides

Kelwa back waters

July -Sep

Salinity ranging
between 1 3 and 28 ppt

Durve (1965)

Bhatia creek

Sept -Nov

Increasing salinity

Mane and Naga¬
bhushanam (1988)

S.cucullata

Ratnagiri

Oct-Jan

Rising salinity and
temperature

Mane and Naga¬
bhushanam (1988)

Someshwar

June -Sep,

Rising temperature

Sukumar and Joseph

Nov-Dec

and salinity

(1988)

Ashtamudi Lake

Nov- Feb,
May-June

Temperature and
salinity

Kripa (1998)

C.gryphoides has two different spawning periods along the Maharashtra
coast. The spawning period is from July to September in Bhatia creek, while
towards south along the Ratnagiri coast, the spawning season is during
September-November. Mane and Nagabhushanam (1988) have analyzed the
hydrographic changes occurring in the oyster beds and found that for
C.gtyphoides, the optimum salinity range for spawning in the Bhatia creek
and Ratnagiri is 13-28 ppt and 23.5-31.2 ppt respectively. Desai and Nimavat
(1983) based on neuroendocrine studies have reported that salinity and
temperature influence the reproduction of C.gryphiodes and C.rivularis.

For S.cucullata, the major spawning period is during the post monsoon in
the different populations along the west coast (Sukumar and Joseph, 1988;
Kripa, 1998).

Oyster Biology and Culture in India

Development

Several investigations have been made to study the development of oyster
eggs and larvae (Brooks, 1880; Galtsoff, 1964). Following description is
mainly summarized from Quayle and Newkirk (1989) and Rao (1983).

The eggs are viable for about 24 hours in the temperate countries while in
the warm tropical waters, the fertilizing power of both egg and sperm lasts
only for 3 to 4 hrs. The embryonic and larval stages are given in Figs. 16, 21
and 22. After fertilization the cells divide rapidly and the first polar body is
observed within 20 to 40 minutes; subsequently the second polar body is
formed. The first cleavage occurs immediately after this and the cells in the
animal pole divide resulting in the 8 -celled stage. After further cell division,
a roughly spherical morula stage is reached. In C. madrasensis in about 2¥i
hrs after fertilization, blastula with cilia is formed and it shows rotatory
movements. This is followed by gastrulation partly by epiboly and partly by
invagination. At the end of 20 hrs, a definite swimming organ called the velum
is formed and these larvae are called ‘veligers’. The velum has a ciliated part
that protrudes outside the open shell and is used for swimming as well as for
food collection. These larvae have limited mobility and move about horizontally
by the water currents. In the first few days, the larvae have a D shape and they
are often called D shaped or straight hinge larvae. The veliger larvae have
alimentary canal, foot and adductor muscle and begin to feed on minute
phytoplankton. Soon, protruberances on the straight hinge line develop and
the larvae become rounder with the formation of umbones. This stage is called
early umbone. Oesophagus, stomach, intestine, digestive gland and rudimentary
gills are formed. In later larval stages, the oysters have two adductor muscles.
The larval shell is different from that of the adult, being less dense and
transparent. This stage is termed the mid umbo stage. Further development
results in the eyed larvae with the formation of an active foot, a cement gland
and black eye spot on each side. The pediveliger is the final larval stage which
is competent to metamorphose and get attached. The pediveliger stage is
characterized by the presence of functional foot, velum, alimentary canal,
eyespot, heart, gill rudiment and two adductor muscles. These larvae can
swim and also descend to the bottom by crawling. This is known as swimming
creeping stage (Carriker, 1961b).

If the pediveliger larva finds a solid substrate, it crawls on it with the help
of foot. If the site is unsuitable the larva continues swimming. On suitable
substrate the pediveliger larva forces from its cement gland a minute drop in
which it crawls and settles with the left valve in the cement. This act of
attaching on a solid substrate is called setting or spatting. The spat is also
known as the seed. Once the spat sets, it is fixed and undergoes several
changes. The foot and the cement gland are detached, the velum is lost, the
body becomes twisted, the anterior adductor muscle is lost and the posterior
adductor muscle is retained and it moves more to the center of the shell. The

Biology

Fig. 16. Embryonic and larval stages of oyster A. Fertilised egg with first polar
body B. Two-celled stage C. Four celled stage D. Blastula E. T rochophore
F. Veliger G. Pediveliger. (Abbreviations: AC-Apical cilia, AM-adductor
muscle, E-eyespot, F-foot, M-mantle, S-shell, ST -Stomach, V- Velum, U-

umbo

Oyster Biology and Culture in India

new shell called the dissconch is quite different from the larval shell
(prodissptonch). The position of umbones of the larvae is used for the
identification of the oyster genera. Crassostrea larvae have prominent umbones
which are opisthogyrate, being twisted posterior to the centre line of the hinge,
while Ostrea larvae have broad umbones that are orthogyrate, being centrally
placed on the hinge line. Tiostrea larvae have no umbones (Quayle and
Newkirk, 1989). Polyspermy will lead to irregular cleavage of egg. In the
brooding chambers of incubatory Osterid species such as Tiostrea lutaria, all
the stages of larval development such as gastrula, trochophore and veliger
have been observed. Attempts were made to rear them outside the parent

oysters. Ex-parent rearing has not been successful for early larval stages, but

■

both veliger and pediveliger stages responded to elevated temperature and
food and settled. In O. edulis the developing larvae are incubated within the
inhalant chamber of the mantle cavity of females for approximately 7 days at
20°C, and afe, released as fully shelled, pelagic veligers into the surrounding
water where the development is completed.

AGE AND GROWTH

Growth is the change in weight/size of an organism or the mean size of
population over a period of time. Growth and survival are the two major
factors, which control the production of a culture unit. Growth can be evaluated
from changes in linear dimensions, volume (in oysters usually the condition
index) or as weight measurement of the whole animal, its live meat weight,
shell weight or dry meat weight (Quayle and Newkirk, 1989). Depending on
the objective of the study such as estimation of production and quality
assessment, the variables are selected. Usually the linear measurements are
taken and the growth estimated.

Growth can be expressed either as absolute or relative terms. Absolute
growth indicates the change in size while relative growth rate gives the rate of
change over a period of time (Wilbur and Owen, 1964). When the size of the
animal over a definite unit of time is plotted, the slope of the time relating size
with time (or age) is the absolute growth rate or velocity of growth (Warren,
1971). Although this gives a growth rate it does not give any indication about
the growth of the animal relative to its size. To account for the difference in
the size, relative growth rate is used and the commonly applied expression is
the instantaneous growth rate. The dimensionless coefficient K is obtained by
the following equation (Malcouf and Bricelj, 1989).

K= [loge L2- loge LJ

n ;.;OH:XV T _ ^

where Lj = the initial length (or other measurement of size)

L2 = the final length

t2 - tj = the elapsed time (usually in days)

Biology

The K coefficient may be multiplied by 100 to express growth as percent
per day. If the growth increment (L2- L^) is small and the time interval (t2 -
tj) is short, an adequate approximation of instantaneous growth rate may be
obtained from the average relative growth rate (ARGR) (Warren, 1971) which
is calculated as

! 1 id i ■. i CH J

L2 L[

ARGR = - - - ! -

(L2 +L.) 0.5 (t2 - t,)

t \ ; • i) i i.) VJt n i , .7 i \ J X

where Lp L2 and (t2 - t,) are as given above.

Growth in oysters depends on several factors such as variations in
temperature and salinity, the availability of food, the time of submergence,
presence of foulers, the degree of crowding and the presence of pollutants
(Galtsoff, 1964; Quayle and Newkirk, 1989; Kennedy, 1996). As the oysters
grow, the cementation of the shell is continued. At the place of cementation,
the prismatic structure of the outermost shell layer is modified to a ridge-and-
furrow structure (Yamaguchi, 1994). The furrows are ultimately filled by the
shell material. At the site of ongoing shell cementation, the mantle margin
presses the shell margin onto the substrate.

Growth in shell length and width of oysters originates from the outer
surface of the outerfold of the mantle edge while the outer surface of the whole
mantle secretes the inner shell surface or nacre, thereby increasing the thickness
of the shell.

Methods of age determination

Growth may be studied by comparing the progression of modal size groups
over a time in the successive length frequencies of a random sample of
population or by measuring the marked or tagged oysters over a period of
time. The first method is useful only when the breeding season is short and a
new brood enters the population as a well defined group with a limited size
range. In such cases each age group appears as a distinct mode in a length
frequency distribution. If the oysters have an extended breeding season, the
offsprings of different broods growing at different rates may mix and it will be
difficult to distinguish the modes. In the marking or tagging method the
oysters are marked by gluing a tag to one valve with a water proof glue or by
drilling a small hole in the umbo of the left valve and tying a tag. A number
can be etched on the shell by an electric drill and protected by covering it with
a transparent plastic. However, in the tropics during certain season due to
severe fouling the number on the tag may not be visible or there are chances
of loosing the tag when the foulers attached on it are removed.

Though length is the most commonly used measurement, other linear
parameters such as width and depth are also periodically observed. Variations
in total weight, meat weight and dry meat weight and their relationship to
length are useful to oyster farmers to plan the harvest.

Oyster Biology and Culture in India

Dimensional and Length- Weight Relationship

Variation in the shell dimensions of C.madrasensis along both the Indian
coasts has been studied. For studying the relationship between length and
weight and other linear measurements, the regression equation Y = a+bX is
used after logarithmic transformation if required (Somasekar et a/., 1982;
Narasimham, 1987; Kripa, 1998). The logarithmic values of observed length
and corresponding log weights showed a linear relationship (r=0.82; P=0. 1 %)
for C.madrasensis in Vellar estuary (Somasekar et al ., 1982). For the same
species and for S.cucullata the length- weight and morphometric relationships
observed by Narasimham (1987) and Kripa (1998) respectively are given in
Table 15. Along the west coast in Cochin estuary, it was observed that the
height and length approximated in oysters of less than 3.5 cm in height
resulting in spat of orbicular shape (Nair and Nair, 1985) while along the east
coast it was 2.5 cm (Rao and Nayar, 1956). In the oyster of shell height 3.5 cm
to 8 cm, increase in height was faster, leading to an oval shape and above 8 cm
the oyster became further elongated (Nair and Nair, 1985).

Table 15. Length-weight and linear relationships in C.madrasensis and S. cuculiata

Species

Parameter (dependent
variable)

C.madrasensis

Total weight*

-3.2421

2.6498

0.96

Shell weight*

-3.3963

2.6678

0.95

Wet meat weight*

-3.9245

2.4110

0.92

Width

7.5634

0.5823

0.84

Depth

5.0008

0.2080

0.65

S.cucullata

Total weight*

-7.5144

2.7649

0.7421

Meat weight*

-9.3594

2.5586

0.7877

Dry meat weight*

-11.1044

2.6002

0.6953

Width

6.8760

0.5310

0.7421

Depth

2.1466

0.4083

0.6387

*after logarithmic transformation

Source: Narasimham (1987) and Kripa (1998)

Growth Rates of Indian Oysters

The first report on the growth of C.madrasensis was made by Homell (1910a)
from Pulicat Lake near Chennai. Further studies on the growth of C.madrasensis
have been made by Paul (1942), Rao and Nayar (1956), Somasekar et al.
(1982), Nayar and Mahadevan (1983), Reuben et al (1983), Joseph and
Madhyastha (1982), Joseph and Joseph (1983, 1985), Nair and Nair (1985),
Narasimham (1987), Yavari (1994) and Velayudhan et al (1995, 2000).

Durve and Bal (1962) investigated the growth characteristics of
C.gryphoides in Kelwa backwaters. Aspects related to biotic potential of
S.cucullata along Karnataka has been reported by Joseph and Joseph (1988),

Biology

while Kripa (1998) has described the age and growth of this species occurring
along the Kerala coast.

The growth of three species of Indian oysters namely C.madrasensis,
C.gryphoides and S.cucullata reported by various authors based on the studies
on natural populations and experimental culture in different water bodies are
given in Table 16.

Table 16. Growth rates of oysters in different water bodies along the Indian coast

Species

Location

Source

Length

Period

Reference

attained

(mon-

(mm)

ths)

C.madrasensis

Bhimunipatnam

Reuben et al. (1983)

C.madrasensis

Kakinada Bay

58-66

Narasimham (1987)

C.madrasensis

Kakinada Bay

8.5

Rao et al. (1994)

C.madrasensis

Adayar estuary

36.8

Rao and Nayar

50.6

(1956)

C.madrasensis

Pulicat Lake

74.2

Thangavelu and

Sanjeevaraj (1985)

C.madrasensis

Vellar estuary

Somasekar et al.

(1982)

112

C.madrasensis

Vellar estuary

Patterson and
Ayyakkannu (1997)

C.madrasensis

Tuticorin

Nayar and

Mahadevan (1983)

C.madrasensis

Mulki estuary

Joseph and

91.5

Joseph (1985)

142

C.madrasensis

Cochin

Purushan et al.

(1983)

C.madrasensis

Ashtamudi Lake

65.9

Velayudhan etal.
(1995)

C.madrasensiss

Sikka

Chhaya et al. (1993)

C.gryphoides

Kelwa

37.2

Durve and Bal (1962)

backwaters

47.9

S.cucullata

Ashtamudi Lake

36.2

Kripa (1998)

51.1

57.2

Ec = Experimental culture; Nb = Natural bed

Among the three species, C.madrasensis has been found to have the
highest growth rates along both the coasts. Growth studies based on samples
collected from the natural bed are few. It has been observed that the growth of
oysters is faster during the initial stages immediately after settlement. Along

Oyster Biology and Culture in India

the east coast, in the natural bed C.madrasensis in Vellar estuary is reported
to reach only 49 mm in one year while in Kakinada Bay it grows to 58-66 mm
during the same period. At both the places suspended experimental culture
studies indicated faster growth rate (Table. 16). Along the west coast, in
Karnataka, C.madrasensis reaches 91 mm in one year indicating a
comparatively higher growth rate than the east coast oyster population. Even
in estuaries where the fresh water influx is high like the Cochin backwaters,
the oysters reach 60 mm in 5 months. The studies in the experimental culture
indicate that C.madrasensis attains about 60 mm length in 6 months and 80 -
90 mm in about one year. However, considerable seasonal variation in growth
rate is observed in all oyster populations. Extreme low salinities during peak
monsoon have been observed to arrest shell growth. Only when the conditions
become favourable, the oysters start their somatic growth and gonad build up.
Factors like high siltation during the monsoon slow down the growth.
C.gryphoides is a slow growing oyster. It reaches only 47.9 mm length in one
year which is almost half that of C.madrasensis. S.cucullata is a small sized
oyster with maximum length of < 60 mm.

CONDITION INDEX

Condition of oyster indicates the degree of fatness of an oyster or the extent
to which the meat fills the cavity. Condition indices are regarded as useful
measurements of the nutritive status of the bivalves. Several studies have been
conducted to measure these variations, which have been reviewed by Walne
(1970). Condition index may also be employed as an assay for monitoring
various pollutants and diseases (Scott and Middaugh, 1978; Scott and Vemberg,
1979; Scott and Lawrence, 1982). The first definable quantitative condition
index (Cl) equation based on the shell cavity has been described by Higgins
(1938). Subsequently, various indices of condition have been proposed. Atleast
six different condition index formulae are currently in use (Crosby and Gale,
1990). Some of the methods used are given below.

Walne (1970) defined a method based on the shell cavity volume

dry soft tissue wt (g) x 1000
internal shell cavity volume (ml)

Walne and Mann (1975) modified the method and used dry tissue weight
as a function of dry shell weight.

dry tissue weight (g) x 1000

dry shell weight (g)

Lawrence and Gordan (1988) proposed the following method
dry soft tissue weight (g) x 100

Cl =

internal shell cavity capacity (g)

Biology

Hawkins et al. (1987) gave another method of determining Cl using shell
cavity capacity.

dry soft tissue weight (g) x 1000
C I ■

internal shell cavity capacity (g)

The shell cavity capacity is determined by subtracting dry shell weight
(g) in air, of a cleaned animal from its total whole live weight (g) in air. The
method using the shell weight is not a measure of how much space is utilized
and does not account for possible variations of internal cavity due to overall
shape and shell thickness variability. It is instead a body component index,
which compares the proportions that soft body tissue and shell weight compose
of the total dry bivalve weight. It cannot be used as an index to evaluate the
nutritive status of the oyster. The method of determining the Cl based on
volume or shell cavity gravimetric capacity should be used for ascertaining the
nutritive status of oysters or to determine whether the animals are under stress.
Crosby and Gale (1990) have recommended that the method described by
Hawkins et al. (1987) as the future standard method for determining bivalve
condition index.

Apart from the numeric or the calculated value of Cl, it is very important
to evaluate the condition of the oyster by visual observation (Quayle and
Newkirk, 1989). The general size of the meat, colour and appearance of the
body surface and mantle thickness are significant parameters. The condition
is good when the colour of the oysters’, body is white to cream (the dark
digestive gland should not be visible) and the mantle is thick.

In the Indian oysters the condition index, determined by the shell cavity
method, is closely linked with the somatic and gametogenic growth. In
C.madrasensis in Mulki estuary, condition index values were moderate (> 20
<70) during the gonadal growth while high values (>70) were recorded during
somatic growth and fattening period (Joseph and Madhyastha, 1982). For the
same species, the Cl values were very high (120 -150) during March -April
and August - September in Tuticorin. It was observed that the Cl values were
high when the diurnal variation in temperature was high (Rajapandian and
Rajan, 1 983). In oyster farming, condition index in the above range is considered
to be good for harvest and less than 70 as unsuitable. In Kakinada Bay, the
condition index was high when the oysters were in the partially spent stage
(April-June) and low when the oysters were in the ‘spent’ condition
(Narasimham, 1987). Durve (1964) observed that in C.gryphoides, the seasonal
variations in condition were related to the gonadal cycles and that the oysters
were in the best condition during October- June when they were not in the
spawning condition.

BIOCHEMICAL COMPOSITION

Venketaraman and Chari (1951) and Easterson and Kandasami ( 1 988) studied

Oyster Biology and Culture in India

the biochemical composition of C.madrasensis of Ennore backwaters and
Tuticorin oyster farm. The range of variation for three components (in
percentage) is given below.

Moisture

Ash

Lipid

Protein

Glycogen

Ennore backwaters

76.7 to 85.0
1.01 to 2.06
1.49 to 2.71
6.93 to 13.31
0.44 to 5.63

Ttiticorin Farm

77.9 to 82.6
3.96 to 6.6
0.20 to 2.20
8.09 to 16.00
*0.9 to 8.6

*Total carbohydrate value determined and hence higher value

QUESTIONS

1 . Describe the basic anatomy of an oyster.

2. Write on food and feeding habits of oysters.

3. Write on types of reproduction and the various larval stages in the life
history of oyster.

4. What is condition index and describe the various methods used in its study?

5. Write short notes on: a) Filter feeding b) D-larva c) Pediveliger larva d)
Condition index e) Oyster shell

Chapter 4

Unwanted Species

THERE are several unwanted species which compete for food, space,
weaken the shell by drilling, prey upon oysters and cause diseases resulting
in oyster mortality. They are dealt in this chapter.

FOULERS

Biofoulers are the unwanted flora and fauna which attach and grow on the
cultured species and on the farm structures. The intensity of fouling varies
depending on the location and the season. Foulers are usually considered as a
nuisance in oyster farming and are called pests. They compete for food and
space with the oysters, and in extreme cases cause mortality.

The main effects of intense fouling on oyster culture are:

1 ) low settlement and high mortality rates of oyster spat;

2) reduced growth rate;

3) increased weight of the farm stock and structures and related floatation
problem;

4) hinderance in harvest and post harvest processes and

5) limitation in marketing as single oyster.

In India, reports on the fouling of oyster beds have been made by several
authors (Rao and Sundaram, 1972; Muthiah et al., 1987; Thangavelu and
Sanjeevaraj, 1988b; Sundaram, 1988 and Kripa, 1998). The commonly
encountered foulers on oysters are given below.

Algae

Seaweeds like Chaetomorpha, Ulva , Enteromorpha, Gracilaria, Cladophora,
Polysiphonia and Gelediella and blue green alga, Oscillatoria are associated
with the oyster population along the Indian coast (Rao and Sundaram, 1972;
Muthiah et al ., 1987; Thangavelu and Sanjeevaraj, 1988b; Sundaram, 1988
and Kripa, 1998). At Tuticorin, Gracdaria has been found to grow densely on
the oyster cages and affected the water flow (Muthiah et al., 1987). Along the
Kerala coast, seaweeds are found in abundance during the monsoon and
postmonsoon seasons (Kripa, 1998). In the mangrove oysters, apart from
these genera other seaweeds lik e Acanthophora spicifera, Caulerpa racemosa,
Derbesia vaucheriaeformis, Cladophoropsis membranacea, Struvea
anastomosans and Dictyota sp. have been reported to occur from the Caribbean
(Littlewood, 1991).

Oyster Biology and Culture in India

Porifera

Along the east coast of India sponges such as Haliclona sp and Hyatella sp.
have been observed on C.madrasensis (Thangavelu and Sanjeevaraj, 1988b).
Reniera tubifera , Pleraphysillia sp., Haliclona spp, Dysidon fragilis,
Mycale sp., Ulosa hispidu, Darwinella rosacea have been noted to foul on
C.rhizophorae (reviewed by Littlewood, 1991). Sponges may be encrusting or
attach solitary.

Coelenterata

Coelenterates, Garveia cerula and Aiptasia tagetes are known to foul on the
oyster C. rhizophorae in Cuba while at Puerto Rico, coelenterates like Pennaria
sp, Bougainvilla sp. and Alcyonium sp. occur on the same oyster species
(Littlewood, 1991).

Bryozoa

Bryozoans are commonly called moss animals. They are colonial. The
encrusting bryozoans are usually less than 1 mm in thickness, but one colony
may completely cover an adult oyster shell (Quayle and Newkirk, 1989). They
are not very harmful to adult oysters but may at times grow over the spat.
Seven species of bryozoans were noted on the oysters in Mulki estuary
(Joseph and Joseph, 1988). In Pulicat Lake, Thangavelu and Sanjeevaraj
(1988b) observed that Scrupoecellaria sp., Schizoporella sp. and a few
unidentified species formed 3.4% of foulers on C.madrasensis.

Annelida

The polychaetes Marphysa gravely i, Eunice sp and Polynoe sp are found in
the crevices between oysters in Athankarai estuary (Rao et al., 1987). Calcarean
polychaete worms Hydroides lunulifera, Spirorbis sp., and Pomatoceros sp.
are the common tube dwelling polychaetes observed on C.madrasensis in
Pulicat Lake and Ashtamudi Lake (Thangavelu and Sanjeevaraj, 1988b; Kripa,
1998). Sabellastarte magnifica, Sabella sp., Spirobis spp., Branchiomma
nigromaculata , Pseudobranchiomma emersoni , and Megalomma sp. are
the common foulers on mangrove oysters (Littlewood, 1991). Avault (1998)
has mentioned that in the Hiroshima Bay during a population explosion of
Hydroides elegans, 6000 oyster rafts were affected and the production dropped
by 60%.

Bivalves

Byssal attaching molluscs and cementing species other than the oyster
sometimes foul the oyster shells. In India, bivalves like Modiolus striatulus ,
M.undulatus, M.metacalfie, Anomia sp. and Perna virdis are the dominant
foulers. In Pulicat Lake, Modiolus sp. formed 8% of the foulers on
C.madrasensis (Thangavelu and Sanjeevaraj, 1988b). In Ashtamudi Lake,

Unwanted Species

they are the dominant foulers during the postmonsoon period in the intertidal
zone (Kripa, 1998). In the tropics Isognomon , Chama and Spondylus have
been considered as foulers (Quayle and Newkirk, 1989).

Crustacea

Barnacles, chiefly of the genus Balanus, are probably the most ubiquitous of
all the fouling organisms. Balanus amphitrite is the main species recorded
followed by B.tintinnabulum. In Pulicat Lake barnacles formed 69.5% of the
foulers, mainly dominated by B. amphitrite (Thangavelu and Sanjeevaraj,
1988b). At Worli in Maharashtra, Sundaram (1988) observed the conical
barnacle Cathamalus stellatus in the S.cucullata beds. Barnacles compete for
food and space in oyster beds. Dead shells provide space for secondary
attachment of foulers. Adult barnacles even prey on oyster larvae (Steinberg
and Kennedy, 1979). In India, barnacles are a menace to spat collection. Their
breeding period almost coincides with that of oysters. Hence spat settlement
gets affected (Kripa, 1998). Sometimes barnacles first settle and the oyster
spat which settles on them easily fall off as they grow. They also affect the
postharvest processes. In Ashtamudi Lake, the barnacles are the dominant
foulers on the oysters in the lower reaches of the Lake.

Chordata

Tunicates or ascidians are known to foul on oyster. Individual tunicates adhere
to the shell by a broad holdfast and the body is enclosed within a test or
envelope. The colonial types of ascidians consist of small tunicate bodies
enclosed in a fleshy encrustation upto 1 cm thick (Quayle and Newkirk, 1989).
Their occurrence is rare in the oyster farms of India where estuarine conditions
prevail. Ascidians like Botrylloides nigrum , Symplegma sp, Diplosoma
listeranum, Lisscolinum abdominale are common in mangrove oysters
(Littlewood and Donovan, 1988).

BORERS

Borers are generally considered as pests of oysters as they do not kill the
oyster but may severely affect their condition and marketability. The shell of
the oyster is bored by these animals and they reside within the shell. They
make the shell brittle, cause blisters on the nacre and make the oysters easy
prey to other predators.

Algae

Algae such as Hyella caespitosa , Mastigocoleus testarum and Gomontia
polyrrhiza penetrate the periostracum and then branch into inner layer of
oyster shells (Galtsoff, 1964). Reports on the perforating algae infecting
oysters in India are not available.

Oyster Biology and Culture in India

Sponges

This group forms one of the commonest borers in oysters. Boring by the
sponge Cliona sp. has been found to be more in the oysters inhabiting the
marine regions of an estuary. Boring is found to be comparatively low in the
oyster population where salinity is low for a long duration. In Ashtamudi Lake
low salinities prevail for prolonged period at the culture sites and hence,
severe damage to the shell has not been observed in both C.madrasensis and
Sacco strea cucullata. Along the east coast also, boring by Cliona has been
observed in C.madrasensis (Thomas, 1979; Thangavelu and Sanjeevaraj,
1988b). Cliona celata, C.vastifica, C.carpenteri, and Aka minuta are the
species of sponges recorded in oysters along the south-east and south-west
coast (Thomas, 1979). Among these C. celata was seen both on C.madrasensis
and S. cucullata while C.carpenteri was seen only in S. cucullata and A. minuta
on C.madrasensis alone. The boring Cliona creates a honey comb of tunnels
in the calcareous shell and the numerous holes they make on the shell increase
the brittleness of the shell (Thomas et al., 1993).

Annelids

The polydorid polychaete worms are found in almost all species of oysters and
are more abundant in low saline, muddy environments. The larvae of these
worms usually settle on the surface of the oyster shell and slowly penetrate
into the shell.

In Pulicat Lake, 9.2% of oysters were found to be infested by Polydora
ciliata. The number of worms in the infested oyster ranged from 2 to 54.
Maximum number was seen in 70-79 mm oysters. The size of worms ranged
from 3 to 42 mm (Thangavelu and Sanjeevaraj, 1988b). Stephen (1978)
observed that in the Crassostrea madrasensis population in Mulki Estuary the
mud worm infestation was very low, almost nil during the monsoon months.
He attributed the reason for low infestation to the almost fresh water condition
of the estuary during monsoon period indicating that continued submergence
in fresh water conditions for prolonged period is detrimental to the mud worm.
Fresh settlement of mudworm was observed with the increase in salinity.

The rate and intensity of Polydora infestation in natural and farmed
oysters ( C.madrasensis ) in Kerala was studied by Ghode and Kripa (2001). In
the natural oyster beds of Ashtamudi Lake, 80% of oysters in the age group
less than 6 months were not infested by the mud worms Polydora ciliata,
while only 44 % farmed oysters of same age were uninfested. In oysters
between 12 to 15 months age, the percentage of uninfested oysters was 48 and
17.4 in natural bed and in farmed oysters respectively. All farmed oysters
above 2 years had Polydora infestation while in the natural bed 2% were still
uninfested.

The intensity of infestation was found to increase with age in both natural
bed and farmed oysters. Severe infestation (> 50 % of the internal shell

Unwanted Species

surface as mud blister) was not observed in small oysters (less than 6 month)
in the natural bed while in the farm 8% of the same age group was severely
infested. In the farm, the percentage of oysters with severe infestation increased
from 14.3 in the first year to 46.5 after 24 months. At the same time in the
natural bed in oysters above 24 months only 38% were severely infested

Bivalves

Lithophaga sp. was found to make long and cylindrical burrows in the shell
of C.madrasensis in Pulicat Lake (Thangavelu and Sanjeevaraj, 1988b).

PREDATORS

In spite of the presence of a hard protective shell, the oysters are preyed upon
by several vertebrate and invertebrate organisms. The mode of predation
varies from simple crushing to paralyzing the oysters. The common predators
are gastropods, crabs, starfishes and fishes. Some flatworms are also known
to predate upon these bivalves.

Flat worms

The turbellarians of the genus Stylochus and Pseudostylochus attack both spat
and adult oysters. They are also known as ‘oyster leaches’ (Galtsoff, 1964)
and “oyster wafers” (Menzel et al ., 1958). It was reported that they caused 30
to 90% oyster mortality along the west coast of Florida during 1916 and 1917.
Extensive mortalities due to flatworms have occurred under typically crowded
mariculture conditions (Provenzano, 1961). P.ostreophagus, a Japanese species,
is found to drill an oval perforation of the oyster spat upto 1 cm in diameter
and is capable of causing considerable mortality (Quayle and Newkirk, 1989).
Flatworms of the genus Stylochus enter the oyster through their partially
gaping valves.

Gastropods

Certain gastropods commonly known as ‘drills’, are common predators of
oysters. They have extensible and flexible proboscis to which is attached a
radula having homy teeth. Associated with this apparatus is an accessory
boring organ whose secretion softens the shell and then with the rasping
action of the radula the shell is scraped to reach the flesh (Carriker, 1961a).
The mechanical radular movements used for drilling are termed “band-over¬
pulley” method (Butler, 1954; Gunter, 1979). Cymatid gastropods, Cymatium
martinanium and C.muricinum are not drilling gastropods; instead they insert
their proboscis between the valves of the oysters and squirt a highly acidic
toxic secretion which is believed to anaesthetize the prey. Melongena corona ,
the crown conch feeds on the oysters without drilling the shell.

In India, Thais rudolphi has been observed to attack young C.madrasensis
in Athankarai estuary (Rao et al. , 1987). In the Tuticorin oyster farm of

Oyster Biology and Culture in India

CMFRI, Cymatium cingulatum has been reported to cause 13% mortality to
oysters (Muthiah et al, 1987). Thais tissoti, Bursa granularis and Drupa
tuberculata are the predatory gastropods recorded in S.cucullata beds in
Maharashtra (Sundaram, 1988).

In temperate countries, oyster drills cause considerable damage in the
commercial farms. Urosalpinx cinerea, Eupleura caudata and Thais
haemastoma are some of the major destructive gastropods (Galtsoff, 1964;
Hofstetter, 1977). The conch Melongena corona and the lightening whelk
Buscycon contrarium are also predators of oysters (Hathaway, 1958; Menzel
and Nichy, 1958; Avault, 1998). In some seasons, the losses have been
estimated at 50% in Louisiana, 85% in Alabama and 90% along Pacific coast
of the United States (May and Bland, 1969; Hofstetter, 1977). The density of
the oyster drills has been found to be highest where salinity is high and most
active in regions of high salinity.

Crustacea

Scylla serrata, the mud crab, has ben observed in the oyster beds of Athankarai
estuary (Rao et al, 1987). In the Tuticorin farm, S. serrata and Pagurus sp.
have caused mortality to spat settled on tiles and rens but loss due to this
predation was negligible (Muthiah et al ., 1987). Crabs are known to cause
considerable mortality in natural oyster population (Krantz and Chamberlin,
1978; Bisker and Castagna, 1987). The stone crab Menippe mercenaria, the
mud crab Panopeus herbstii, rock crab Cancer irroratus and the blue crab
Callinectes sapidus are the common predators of oysters (White and Wilson,
1996; Bisker and Castagna, 1987). The blue crabs use different methods to
open the oysters depending on the size of the prey; small oysters are crushed,
while the adult oysters are devoured by chipping of their shell edge (Krantz
and Chamberlin, 1978). They feed on oyster spat by cracking the shell. Spat
set on collectors have been destroyed by crabs. Hermit crab, Eupagurus
berhardus is known to attack and devour oysters whose shells have been
damaged during declustering. One method of eradication of predatory crabs is
to lay baited traps around intertidal spat collectors and cultivated oysters. In
some regions where the blue crabs are consumed, it may be an additional
source of income to the farmer.

Echinoderms

Sea stars are a menace in the oyster farms in the temperate region. Greatest
harm is done when the oysters are grown by the on-bottom method and also
during the spat collection period (Galtsoff, 1964). Asterias forbesi is an
important predator. An oyster, between 75 and 100 mm in length may be
devoured by a starfish in less than 24 hours (Quayle and Newkirk, 1989).
Starfish predation has not been reported in the oyster farms in India.

Unwanted Species

Fishes

Striped burrfish Chilomycterus schopfi , the goby Gobiosoma bosci, the toad
fish Opsanus tau, the cow-nosed ray Rhinoptera bomasis, Summer flounder
Paralichthys dentatus. Puffer fish Diodon hystrix, skates Raja spp.prey on
oysters (Hoese and Hoese, 1967; Littlewood, 1991; White and Wilson, 1996).
The black drum Pogonias cromis, the diamond sting ray Dasyatis dipterurus
are predators of oysters. These fishes use their powerful teeth to crush the
oyster shell.

Birds

Blue bills, Nyroca marilla and Nyroca ajfinis and the white winged scoters,
Melamita deglandi prey upon oysters (Galtsoff, 1964). Bird predation of
oysters has not been reported from India.

Size related predation

Predation by gastropods and crustaceans is related to the size of the oyster. The
blue crab Callinectes sapidus, the stone crab Menippe mercenaria and the
common rock crab Cancer irroratus are noted for the size related predation.
It has been observed that rock crab, mud crab and the American lobster
Homarus americanus could not attack larger oysters (> 30-35 mm) (Elner and
Lavoie, 1983). Similarly, flatworms also have shown preference for small
oysters. Stylochus ellipticus preferentially attacks small oysters, but large
flatworms can kill oysters as large as 6 cm (Landers and Rhodes, 1970). Size
of the predator influences the intensity of destruction of the oyster bed. Adult
starfishes have been found to cause more mortality than younger ones
(MacKenzie, 1970). Fishes have also shown size related predation. Nearly all
oyster predators are limited to consuming smaller oysters but drumfish and
cow-nosed ray can prey upon oysters above 8 cm (Smith and Merriner, 1978).
It has been reported that the conch Thais sp. could eat almost 100 small oysters
per day. Although they attack large oysters, they prefer the oyster spat (May
and Bland, 1969; Hofstetter, 1977).

Thangavelu and Muthiah (1983) observed that C. cingulatum attacked
oysters of size 25 to 85 mm and the modal size of oysters killed was 53.3 mm.
Nearly 75% of the oysters were in the size group 40-65 mm. Muthiah et al.
(1987) observed that size of C. cingulatum was also related to the size of oyster
which is preyed upon. They noted that gastropods of size 45 mm preyed upon
oysters of 39 to 64 mm with a mean size of 49.7 mm. Cymatium of 74 mm
shell length preyed upon oysters of mean size 68.5 mm.

CONTROL OF FOULERS, BORERS AND PREDATORS

Fouling can be controlled by physical, chemical and biological methods.
Physical methods involve manual removal of foulers or moving of the oyster
string/oysters away from the site. It is labour intensive and increases the

Oyster Biology and Culture in India

operational expenditure of the farming systems. Chemical methods indicate
dipping the rens in chemical solution for a fixed period. Though the method
is effective, care should be taken to choose right chemical (Table 17). It should
be non-toxic and should not affect the oyster meat. After understanding their
ecological impact and other fauna they can be used to control fouling.

By placing a few dogwhelks ( Nucella lapillus) in the oyster trays, fouling
by mussels is reduced since they prefer to prey on small mussels. Most snails
under Tritinidae do not have pelagic larvae and it is suggested by some
workers that the best method to control these gastropods is to collect them
when they aggregate for breeding and egg deposition. It has been observed
that the rock crab Cancer irroratus, when present in the oyster trays, fouling
was low. A species of Haliphthoros has been proposed as a possible candidate
for biological control of the oyster drill. The probable effects it may have on
other fauna are not known. Oysters prefer light settlers while barnacles prefer
dark (Avault, 1998). The different methods used for controlling the foulers,
borers and predators of oysters are presented in Table 17.

In India, experiments were conducted to eradicate mud worms by dip
treatments in formalin, chlorine and freshwater (Ghode and Kripa, 2001).
Formalin treatments in three different doses, 1000,500 and 250 ppm for 30
minutes, 1 hour and 2 hours respectively resulted in removing 79.6%, 69.1%
and 69.6% worms from oysters with low mortality (6.6, 1.6 and 0% mortality).
Eradication treatment using chlorine at doses 1000, 700 and 500 ppm for 3, 5
and 6 hours were successful in eliminating 78.3%, 65.1% and 57.7% worms
respectively from shells with test oyster mortality of 15%, 11.6% and 3.3%.
Freshwater treatment for 3, 6, 9 and 12 hours and aerial exposure after
brushing the oysters with formalin were not effective in eradicating mudworm.

PARASITES AND DISEASES

Parasites and diseases cause large-scale mortalities of oysters in several parts
of the world. During the last three decades, a multidisciplinary approach
towards understanding the causes of major oyster mortalities that occurred in
Europe, the United States and Japan has been made. In some cases (eg. Dermo
disease) it has been possible to identify the etiological agent and document its
life cycle, mode of transmission, effects of disease on the host, the defense
mechanism and the influence of the environment (Sindermann, 1990; Ford
and Tripp, 1996). Several publications have summarized the known diseases
and parasites of oysters (Lauckner, 1983; Sparks, 1985; Sindermann and
Lightner, 1988; Fisher, 1988; Elston, 1990, 1993; Sindermann, 1990; Perkins,
1993; Bower et al. , 1994; Ford and Tripp, 1996). Not much work has been
done on oyster pathology in India. A brief description of the commonly found
parasites and the principle infectious diseases of oyster are given further.

Unwanted Species

Table 17. Physical, chemical and biological methods generally employed to control the
foulers, borers and predators of oysters.

Control method

Organism controlled

Remarks

Suction devices

Predators and
competitors

Removes the buried
predators

Mops made of iron beams
with bundles of rope yarn

Removes mainly
starfishes by
entangling

Harmless to oysters

Flaming: passing a flame over

Removes foulers

Harmless to oysters

oyster shell after drying

Air drying: exposure to sun

Destroys early stages
of sponge, tunicates
and algae/seaweeds

Harmless to oysters: but
controls only to small
extent.

Scraping, scrubbing and jet

Larval stages, egg

Controls only to

washing

cases and larger
foulers

certain extent

Chlorinated hydrocarbon

Oyster drills and
other predators

Uptake by oysters may
affect their quality,
regulation set by FDA
and EPA

Dip treatment in rock salt

Predators

Harmless to oysters

solution followed by aerial
exposure

Quicklime applied through

Controls starfish

Harmless to oysters

pumps @ 300 kg/ha

Dipping in hot water (55-60°C)
for 10 to 15 sec; in fresh water

Controls foulers
and borers

Harmless to oysters

for 30 to 50 hours, dipping in
brine solution

Avoiding placing spat

Avoidance of large

Information on the

collectors during breeding

scale settlement of

ecology and breeding of

season of foulers

barnacles, Modiolus
and calcareous
polychaetes

foulers is essential to
employ the method

Growing other compatible

General fouling

Selection of compatible

species which can eliminate
the fouler (biological control)

organism

species and under¬
standing of their mode
of action are essential

Parasites

Not much information is available on the parasites and diseases of the tropical
oysters. Oysters are infected mostly by parasitic helminths and crustaceans.
These are internal parasites and usually their effect on the host is considered
as sublethal. Molluscs are sometimes encountered as ectoparasites.

Helminth parasites. Trematodes, Cestodes and Nematodes are the
Helminth parasites of molluscs. Among these, trematode larvae are considered

Oyster Biology and Culture in India

as the most important. They use molluscs as the first intermediate host (with
sporocyst, redial and cercarial stages) or as second intermediate host
(metacercarial stage). In some instances, the mollusc may act as host for both
the stages (Sindermann, 1990). Bucephalus haimeanus, B.cuculus and
B.longicornutus are known to infect oysters (Howell, 1966; Sindermann,
1990). Sporocysts and cercariae of Bucephalidae are parasitic in oyster,
metacercaria in small fish and adults in predatory fish. Sporocysts of the genus
Bucephalus occur in the gonads and digestive gland of the oyster and may
spread to gills, mantle and even adductor muscle. They are known to cause
sterility to the host. Menzel and Hopkins (1955) observed that early infection
temporarily stimulated growth of the host, but more severe infections retarded
it. Metacercaria of Gymnophalloides tokiensis (whose definite hosts are marine
birds) and Protoeces ostreae are found in Japanese oysters (Ching, 1972).
Larvae of Protoeces maculates are reported in European oysters. Massive
infestation by the larvae of Ac anthopary phium spinulosum, with an average of
45 worms per oyster has been observed in American oysters (Little et al.,
1966).

It has been observed that some of the trematodes which infect the oyster
are hyperparasitized by haplosporidians. Howell (1967) has described
Urosporidium constantae from Bucephalus longicomutus parsitizing Ostrea
lutaria. The haplosporidean completely destroyed embryonic cercariae within
the sporocyst system. Another hyperparasite is the microsporean Nosema
dollfusi of B.cuculus in C.virginica (Sprague, 1964).

In India, trematode parasites have been observed in C.madrasensis (Samuel,
1976; Joseph, 1978; Stephen, 1978; Thangavelu and Sanjeevaraj, 1988c).
Samuel, (1976) observed infestation by the cercaria of Bucephalopsis
haimeanus , a trematode on C.madrasensis. He observed that in the infected
oysters, the gonads externally appear well developed and mature, but internally
they were devoid of eggs or sperms; the only contents were the cercaria and
tissue fluids. The parasites were densely packed in a system of ramified
tubules. In two of the infected oysters, the flesh weight was higher (gigantism)
compared to that of the uninfected one of the same size group. Only 1 % of
the oyster population was infected. Stephen (1977) has reported that 0.61 %
of oysters from Mulki estuary were infected by the larvae of Bucephalopis sp.
The primary site of infection by larval trematode, Bucephalus sp. in Crassostrea
madrasensis was the mantle (Joseph, 1978). The infection seemed to spread
to digestive gland, normal site of gonad, gills, and finally the labial palps. The
adductor muscle was never infected. The sporocysts were long, tubular,
multibranched and tangled, measuring from 24 to 368 pm in width. Signs of
total inhibition of gametogenesis were evident in all the infected oysters
(Joseph, 1978). Infestation by trematodes Bucephalopsis haimeanus was
observed in the gonads of C.madrasensis in Pulicat Lake (Thangavelu and

Unwanted Species

Sanjeevaraj, 1988c). Initially the infection was found in the gonads of oyster
and later it was found to invade other tissues such as mantle, gill and digestive
gland. Infection was more in partially spent and spent oysters than in fully ripe
and developing gonads. In infected oysters, the gonads were quickly resorbed
and thus the oysters were castrated, leading to indeterminate stage. Almost all
sizes of oysters from 20 to 129 mm were infected. The extent of infection
varied with size groups. Oysters of 60-69 mm and 100-109 mm size groups
were more heavily infected. The parasites were observed to die at a salinity of
2-3 ppt. Thangavelu and Sanjeevaraj (1988c) observed strong influence of
salinity on the infection by trematodes in oysters. They found that when
infected oysters are exposed to low salinity of 4.52 ppt, the percentage of
gonad infection was reduced from 12.7 to 0.84 after a fortnight. On further
exposure for a fortnight to low salinity (3.92 ppt), the oysters were completely
devoid of infection.

Oyster populations in several regions of the world are parasitized by
larval cestodes. The coracidium of the Tylocephalum was reported in the
stomach and gills of American oysters. The response of the host when infected
by parasites has been studied in some instances. The parasite Tylocephalum
sp. does not seem to damage the host significantly, but a thick fibrous cyst is
formed around the metacestode. Cheng (1996) showed that the host did not
respond appreciably while the parasite penetrated the gut wall, but reacted to
it when came in contact with the underlying connective tissue by enclosing it
with a complex capsule of brown cells, connective tissue fibers and haemocytes.
Stephen (1978) has observed the larvae of the cestode Tylocephalum in
C.madrasensis.

Nematodes are an inconspicuous group of parasites in oysters. They occur
as larvae. Echinocephalus sinensis ( =Echinocephalus crassostreai ) was reported
from C.gigas (Ko et al., 1975)

Crustacean parasites. The common crustacean parasites of oysters are
copepods and crabs (pinnotherid). They are not considered as very significant
pathogens, but may cause occasional mortalities under unfavourable
environmental conditions. Among the copepod parasites, Mytilicola orientalis ,
known as the red worm or le cop rouge, is an intestinal parasite which occurs
in the host’s gut. This species was first observed in C.gigas in Japan (Mori,
1935) and it was introduced to U.S. when the oyster seed were imported from
Japan. From then it even spread to the native oyster species O.lurida (Chew
et al., 1964). The parasitic copepods were introduced to France also when seed
and adult oyster (C. gigas ) were imported from Japan and North America
(Sindermann, 1990). The infected oysters had a lower condition index than the
uninfected one. Mytilicola orientalis has been found to affect the gut of
C.gigas. Normal tall columnar epithelium was reduced to squamous or cuboidal
epithelium and cilia were lost from cells in contact with the parasite. In some

Oyster Biology and Culture in India

cases, the parasite penetrated into the gut wall destroying the mucosa (Sparks,
1962). In C.glomerata, Pseudomyicola spinosus causes haemocytosis in the
connective tissue beneath the epithelium of the gut wall where appendages ot
parasite are inserted (Dinamani and Gordan, 1974).

The pinnotherid crabs, commonly called the pea crabs inhabit the mantle
cavity of oysters. They are cited as the main cause for the unusual mortalities
that occurred in Delaware Bay in 1941 (Stauber, 1945). Atleast 90 % of the
oysters were reported to harbour four to six crabs. However, in the following
years, the abundance declined considerably. They were reported to cause the
gill and palp lesions, weight loss, and reduce the filtering ability of the oyster
(Haven, 1959). In Madagascar, Poisson (1946) reported that a characteristic
irritating flavour developed in oysters which were parasitized by the pinnotherid
crab. However, he speculated that this flavour might be due to the coelenterate
Sertularia which often grows on the shells that contain Pinnotheres. They
have also been considered to have symbiotic relationship with oysters rather
than parasitic (Quayle and Newkirk, 1989).

The pea crab Pinnotheres sp. has been reported in Saccostrea cucullata
(Awati and Rai, 1931), in C. gryphoides (Durve, 1964) and in C.madrasensis
(Narasimham, 1987; Joseph and Joseph, 1988).

Molluscan parasites. The ectoparasitic gastropod Boonea impressa attaches
its proboscis to the oyster’s mantle and then pierces the host’s gut wall with
a buccal stylet and sucks the body fluids. They may occur in high densities;
nearly hundred snails have been reported on a single oyster (Robertson, 1978).
Ward and Langdon (1986) found that B. impressa reduced the energy available
to oysters for growth and maintenance.

Diseases

In the last century, the natural oyster populations and the farmed stock in many
parts of the world have been affected by catastrophic mass mortalities bringing
the oyster industry to a stand still for many years. One of the earliest mass
mortalities of oysters reported in scientific literature was the maladie du pied
which occurred in the Arachon Basin, France in 1 877 affecting the oyster
Ostrea edulis. In Europe, mass mortalities of O. edulis were reported during
1919 to 1923 due to an unknown causative factor (Korringa, 1952). In 1930,
the shell disease caused by the fungus Ostracoblabe implexa was responsible
for mass mortalities of O. edulis and C. angulata. These two species were
again affected by another disease, the digestive gland disease caused by
ascetosporan, Marteilia refringens and the gill disesase in the 1960s and 70s.
In 1979, extensive stocks of the European flat oyster were destroyed by the
disease-bonamiasis caused by the protozoan Bonamia ostreae. Mortalities due
to this disease reached 80% in the French oyster growing areas (Poder et al .,
1982.).

Unwanted Species

The natural populations of oysters have been supporting well established
fisheries in many countries. These natural oyster beds have witnessed severe
outbreaks of diseases. The C. virgina population of Canada was hit by the
Malpeque Bay disease (1915 - 1939, 1955). The impacts were so severe that
it took nearly 20 years to return to the previous level of abundance (Logie,
1956). Mortalities due to the protistan parasite Dermocystidium marinum
(now called Perkinsus marinus ) in the Gulf of Mexico began in late 1 940’s
(Mackin et al. , 1950). The annual mortalities were more than 50% in this
region (Ray et al ., 1953). In the following decade, Haplosporidium nelsoni
caused extensive mortalities accounting for above 95% leading to drastic
decline in the fishery (Farley, 1968). In New Jersey waters of Delaware Bay
the production which fluctuated around 2724 tonnes during the late 40’s and
early 50’s declined to 75 tonnes in 1960.

In Asia, the C.gigas population in different regions of Japan viz. Kanasawa
Bay, Miwura peninsula, Hiroshima Bay and Matsushima Bay suffered large
scale mortalities during 1915 to 1960 due to unknown reason (Sindermann,
1990). The cause for the mortalities were related to metabolic disturbances
associated with spawning (Mori et al ., 1965). Koganezawa (1975) related
these mass mortalities to the developments in hanging methods of oyster
farming. Further information on these mass mortalities of oysters in different
regions is available in the reports of Gross and Smith (1946) and Sindermann
(1968a, 1968b, and 1990). In India large-scale mortalities in oyster population
due to diseases have not been reported.

The common symptoms of disease in oysters as summarized by Galtsoff
(1964), Quayle and Newkirk (1989), Sindermann (1990) and Ford and Tripp
(1996) are: retarded growth, failure to fatten resulting in thin watery meat, lack
of gonad development, recession of mantle, slightly gaping valves and
discolored dirty green or brown body. A brief outline of the main diseases is
given below.

Viral diseases: The first report of viral disease in oysters was by Farley
et al. (1972) on a herpes-type infection in C.virginica. Since then considerable
work has been done on oyster mortalities which seemed to have a viral
etiology (Farley, 1978; Sparks, 1985). The major viruses reported to infect
oysters are given in Table 18. Sindermann (1990) has commented that “the
viral agents are latent in the natural population but may become patent under
conditions of environmental stress”.

A major viral disease is the gill disease, also known as maladie des
branchies , which was responsible for severe mass mortalities of C.angulata
on the French coast in 1996. This resulted in 70 % mortality of oysters in
culture areas. An iridovirus resembling lymphocystis virus of fish was identified
as the disease agent (Comps and Duthoit, 1976). These were found to affect
the gill and palp tissues leading to destruction of filaments, gill erosion and

necrosis.

Oyster Biology and Culture in India

Ovacystosis is another viral disease which is caused by Papovavirus in
C.virginica (Farley, 1973; Meyers, 1981). They cause massive hypertrophy of
gametocytes and eggs. The larvae of C.gigas have suffered large-scale mortalities
(upto 50 %) due to the attack of icosahedral virus. This is known as the Oyster
Velar Virus Disease (OVVD). They occur in the velar epithelial cells of larvae
and cause velar and mantle erosion (Elston and Wilkinson, 1985).

Table 18. Viruses reported to infect the commercially important oysters.

Host

Virus type

Effect on host

References

Ostrea edulis

IPN-like virus

Experimental infections
caused necrosis of digestive
tissue, with infiltration of
hemocytes; general tissue
edema; increased mortality
rates in experimental
populations.

Hill and

Alderman

(1979)

Crassostrea

Herpes-type

Mortalities when animals

Farley et al.

virginica

stressed by high temperatures.
Dilated digestive diverticula,
and aggregation of cells in
connective tissue
surrounding blood sinuses.

(1972)

Papovavirus

Lysis of infected cells;
low prevalence. Isolates

Farley (1973)
Meyers (1979)

Reo-like virus

were cytopathogenic for fish
cell lines, but no oyster
pathology was reported.

Meyers and

Hirai (1980)

Crassostrea

Herpes-type

Associated with enzootic

Alderman

gigas

(presumptive)

“summer disease” of C.gigas.

(1980)

Icosahedral

Velar and mantle erosion;

Elston (1979,

virus

epizootic with mortalities of
larvae of up to 50%; called
oyster velar virus disease
(OVVD).

1980)

Iridovirus

Gill erosions, similar to those
seen in maladie des branchies
of C. angulata, but of lesser
severity than in that species

Marteil (1968)

Icosahedral

virus

(presumptive)

Causes grayish discoloration
of visceral mass

Comps (1978)

Crassostrea

Iridovirus

Identified as cause of

Comps and

angulata

maladie des branchies,
causes gill erosion and
necrosis, hypertrophy of gill
epithelial cells.

Duthoit (1976)

Fungal diseases: Diseases caused by fungi are only a few and, in the
natural population, they mainly attack the shell. Fungal attacks occur in oyster

Unwanted Species

hatchery but they are not as severe as the bacterial infection.The “shell
disease” ( maladu du pied) also known as the foot disease of O.edulis is one
of the most severe diseases of oysters and has been recognized for more than
a century. Its etiological agent was first described as a bacterium but further
studies disclosed the common occurrance of a fungus. The infection occurs in
the shell under the adductor muscle attachment where it causes blisters on the
shell and degeneration of the adjacent muscle tissue. The muscle becomes
detached as irregular cysts were formed. A disease characterized by the
formation of green or brown pustules caused by Monilia was also reported
(Sindermann, 1990).

Cole and Hancock (1956) have described two distinct diseases in European
oysters, the typical one characterized by greenish rubbery warts and knobs
inside the shell particularly in the region of muscle attachment, and an atypical
form in which young oysters had thickened margins with numerous white
patches but had no deformation of the muscle attachment area. Alderman and
Jones (1967) have identified the etiological agent as a phycomycetes fungus
(< Ostracoblabe implexa ) possibly a member of Saprolegniaceae, which is
present in the shells of diseased oysters.

In India, Durve and Bal (1960) reported on the occurrance of a shell
disease in C.gryphoides. Another fungus described as Ostracoblabe implexa
was isolated from shell lesions of the rock oyster S.cucullata by Raghukumar
and Lande (1988). Direct shell-to-shell transmission was possible under
experimental condition.

Bacterial diseases

Larval vibriosis. Larvae of oysters have been found to be more susceptible
to bacterial diseases than adult oysters. Experimentally it has been proved that
adults can tolerate high population of bacteria but larvae succumb to disease
(Guillard 1959; Tubiash et al., 1965). Vibriosis or bacillary necrosis has been
recognized as an important disease of bivalve larvae in hatcheries. An exotoxin
produced by Vibrio sp. has been reported to cause 100% mortality of oyster
larvae (Sindermann, 1990). Pathogenic strain of Pseudomonas has also been
responsible for larval mortalities.

Commercial oyster hatcheries have often faced rapid epizootic mortalities
in the larval culture due to vibriosis (Tubiash et al., 1965). Two species have
been identified, Vibrio anguillarum and V.alginolyticus (Tubiash et al., 1970).
The bacterial cells are gram-negative rods, 0.6 to 10 pm long, and motile with
polar monotrichous flagella (Elston, 1990). Though the larvae can be treated
with antibiotics, routine application is not recommended because of the potential
for developing resistant strains (Brown and Losee, 1978; Elston, 1984). The
disease outbreaks can be minimized by reducing the stress factors such as
overcrowding, high temperature, insufficient food, or inappropriate oxygen
tension (Tubiash, 1975; Elston, 1984).

Oyster Biology and Culture in India

Juvenile oyster disease (JOD): Juvenile Oyster Disease has caused high
mortalities in hatcheries in United States where the juveniles of C.virginica
are reared in extensive systems. The mantle and hinge ligament are affected.
In some oysters, the attachment of the adductor muscle to the shell degenerates.
The most characteristic symptom of JOD is the presence of an anomalous
organic deposit inside one or both valves. It is formed between the mantle and
inner shell and is usually raised into a ridge around the mantle edge (White and
Wilson, 1996). The etiological agent of JOD has not been confirmed.

A protistan parasite is considered to be associated with JOD (Farley and
Lewis, 1993). It has also been suggested that rapid secretions of conchiolin
layer is a reaction to same type of irritant (Bricelj et al. , 1992). The toxic
blooms caused by the dinoflagellates Gymnodinium sanguineum, and the red-
tide causing ciliate, Mesodinium rubrum were investigated, but no direct
relationship to JOD was observed (Bricelj et al., 1992). High densities of
M. rubrum and Gymnodinium spp. frequently lead to bacterial blooms (especially
Vibrio). The bacteria use nutrients from the decaying plankton (Romalde et
al., 1990). It is assumed that a combined effect of these factors may be the
cause for JOD. A bacterial etiology has also been suggested. In tissue section,
bacteria were found in mantle lesions and anomalous conchiolin deposits of
some oysters (Bricelj et al., 1992). Although the causative agent has not been
identified, the disease can be transmitted in the laboratory to unaffected
oysters by proximity to disease bearing individuals (Lewis, 1993). The control
measure suggested was to increase water circulation in rearing containers of
juvenile oysters (Bricelj et al., 1992; Ford, 1994)

Bacterial infections have been observed in adult oysters also. Vibrio-
induced cardiac edema was reported in low prevalence in oysters of Chesapeake
Bay (Tubiash et al. , 1973). The isolates of pericardial fluids contained high
densities of V.anguillarum which are pathogenic experimentally to oyster
larvae, but adults were not affected. In Japan, mass mortalities of C.gigas in
Hiroshima Bay in the early 1960’s occurred due to “summer disease” (Numachi
et al., 1965). Similar sporadic mortalities of C.gigas have occurred in North
America since the early 1960’s. Pseudomonas enalia and Vibrio
parahaemolyticus have been isolated from the dying oyster (Colwell and
Sparks, 1967; Lipovsky and Chew, 1971). However the general conclusion
about these summer mortalities is that this disease is probably of bacterial
etiology, possibly aggravated by physiological stresses of spawning and high
water temperatures (Sindermann, 1990). A bacterium of the genus Nocardia
has been linked with summer mortality (Friedman and Hedrick, 1991).

Protozoans: Some oyster diseases which were responsible for collapse of
natural oyster population are caused by the protozoan parasites. The etiological
agents for the Delaware Bay disease (MSX), the seaside disease (SSO), the
Dermo disease, aber disease and bonamiasis are protozoans. The principal

Unwanted Species

protozoan pathogens of oysters are listed in Table 19. The salient features of
the major protozoan diseases in oysters are given below.

Table 19. Principal protozoan pathogens of oysters

Host

Disease name

Pathogen

Effect on host

Crassostrea

virginica

Delaware Bay
disease, MSX
disease

Haplosporidium

nelsoni

Mass mortalities upto 95%
occurred in North America in
late 1950s

C. virginica

Seaside
disease (SSO)

Haplosporidium

ccstale

Causes early summer
mortalities with sharp peaks

Ostrea edulis

Digestive
gland disease,
Aber disease

M arte ilia
refringens

Mass mortalities up
to 90% on French

Atlantic coast

O.eduiis

Bonamiasis,

hemocyte

Bonamia

ostreae

Epizootics and continuous
mass parasitosis mortalities
began in 1979 and spread
quickly to all growing areas

C. virginica

Dermo

disease

Perkinsus

marinus

Mortalities since the

1940s in the Gulf of Mexico;
persistent annual mortalities
in high salinity waters

Dermo disease The extensive oyster mortalities in the Gulf of Mexico
were caused by the Dermo disease. The etiologic agent was first thought to be
a fungus, Dermocystidium marinum (Mackin et al., 1950). Later, based on its
similarities to parasitic coccidians, it was placed in the phylum Apicomplexa
and renamed as Perkinsus marinus (Levine, 1978). Recent studies using small
subunit ribosomal RNA sequences, suggest that Perkinsus spp. may be more
closely related to dinoflagellates (Fong et al., 1993; Siddal et al., 1995).
Prevalence of this parasite is more than 50 % in most of the oyster growing
areas of Gulf of Mexico (Craig et al., 1989). The oysters may get infected
through feed (Perkins, 1988) or by parasites released into water by disintegration
of dead oysters and also through faeces of live oysters (Bushek et al., 1994).
It has been observed that the haemolymph sucking snail Boonea impressa acts
as a vector in the transmission of P.marinum in other live oysters.

In the infected oysters, several biochemical and biological changes have
been observed. Decrease in tissue amino acid concentration (Paynter et al.,
1 995) and an increase in the taurine - to - glycine ratio, similar to that reported
for molluscs stressed by other infectious and non-infectious diseases (Soniat
and Kaenig, 1982) have been observed. Shell and soft tissue growth retardation
and decrease in the percent of gonad area were some of the biological changes
observed (Ray et al., 1953; Dittman, 1993). The host responds to Dermo
disease by increasing the circulation of haemocytes and their infiltration into
the affected area.

Oyster Biology and Culture in India

High temperature (>25 °C), and salinity (>9 to 10 ppt) have been found
to increase the activity of the parasite (Ford and Tripp, 1996). The severity of
the disease is increased by the parasitism by the snail Boonea impressa (White
et al ., 1987) and by some chemical pollutants in the environment (Winstead
and Couch, 1988; Wilson et al., 1990). The control measures suggested are
avoiding planting of infected oyster in new areas and by using cycloheximide
(Calvo and Burreson, 1994).

MSX disease: The mass mortalities of oyster in North America in 1957
and 1959 were due to a disease commonly known as MSX with a protozoan
as the etiological agent (Haskin et al., 1965). It was given the acronym MSX
because it was found as multinucleated (plasmodial) stage with unknown
affinity, thus named multinucleated sphere X (Haskin et al., 1965). Later it
was identified as Haplosporidium (formerly Minchina ) nelsoni a spore forming
pathogen (Levine et al., 1980). In the last decade, phylogenic comparision
using 16S (small subunit)-like ribosomal RNA gene sequences suggested that
haplosporidians are more closely related to alveolates (ciliates, dinoflagellates
and apicomplexans) than to other spore forming protozoans such as
microsporidian (Siddal et al., 1995). The mode of transmission is not known.
Despite many attempts, it has not been possible to transmit the disease in
controlled condition. The portal of entry of H. nelsoni is through gill and palp
epithelia (Ford and Tripp, 1996) while P.marinus and H.co stale, other two
major parasites invade the host through the lining of digestive system.

The growth of infested oysters is retarded (Matthiessen et al., 1990), the
condition index lowered (Barber et al., 1988; Ford et al., 1988) and clearance
rate reduced to half (Newell, 1985). Variation in biochemical composition has
been reported with low levels of lipid glycogen and protein.Temperature and
salinity affect the infection of H. nelsoni (Ford and Haskin, 1982; Andrews,
1964). High temperature and low salinity were correlated with reduction of
infection (Andrews, 1983). Metabolic effects of MSX on oysters are aggravated
by other stressors such as concurrent infestation by Polydora websteri
(Little wood and Ford, 1 990). The most effective method to control the infection
is by using disease resistant strains produced in the hatchery (Ford and Tripp,
1996).

SSO disease: The SSO disease (“SSO” for seaside organism) is reported
to occur in C.virginica in North America. The causative agent is a protozoan,
Haplosporidium co stale which is closely related to H. nelsoni. The method of
transmission of this parasite is not known. It has not been possible to infect
fresh uninfected oysters by feeding and injection of spores. It has been
observed that oysters become infected only during exposure periods when
sporulating H.co stale are found in previously infected oysters. The entry into
the oyster is through the digestive epithelium. Development of the pathogen
is enhanced in salinities greater than 30 ppt. The development of lethal

Unwanted Species

infection by H.costale requires exposure during a well-defined 2-month period
followed by an incubation period of nearly a year (Ford and Tripp, 1996). The
oyster farmers plant and harvest the oyster by avoiding the periods of high
mortality.

Digestive gland disease: The digestive gland disease or Aber disease is
caused by the ascetosporan Marteilia refringens. The disease was responsible
for the mass mortalities of O.edulis (upto 90 %) on French Atlantic coast in
1967. It has been reported to affect oysters in Spain and Holland (Sindermann,
1990). The pathogenic parasite mainly affects the intestine and digestive gland
tubules. In infected oysters, the digestive gland becomes pale and the meat
becomes thin (Morel and Tige, 1974).

Bonamiasis: The ascetosporan parasite Bonamia ostreae is the etiological
agent for the disease Bonamiasis. The O.edulis population in France suffered
large scale mortalities due to the attack of this parasite in 1979. The disease
spread to Netherlands when infected oysters were imported from France
(Grizel and Tige, 1982; Balouet et al. , 1983). Consequently, in Netherlands,
an extensive programme to remove all oysters from the infected areas was
implemented and this curtailed the disease (van Banning, 1982, 1985). The
infected oysters get a yellow discolouration. Presence of gill lesions and
“microcells” has been reported (Sindermann, 1990). Another species of the
genus Bonamia has been reported to cause mortalities upto 63 % in wild
population in 1986 (Dinamani et al., 1987).

In India, samples collected and analysed from the natural oyster beds
around Tuticorin in 1984-85 indicated the occurrence of Perkinsus marinus ,
which ranged from 10 to 60%. The weighted incidence ranged from 0.05 to
0.36 (Muthiah and Nayar, 1988).

Other protozoan parasites: Mass mortalities of rock oysters,
S.commercialis, in Australia have been reported during the 1970’s. The causative
agent of this has been identified as an ascetosporan Marteilia sydneyi (Wolf,
1972; Perkins and Wolf, 1976). Necrosis of the digestive gland epithelium and
retardation of gonad development have been observed in infected oyster.

Apart from the protozoan parasites which caused large scale mortalities,
the occurrence of other protozoa in different species of oysters has been
reported (Ford and Tripp, 1996). Hexamita nelsoni is a cosmopolitan flagellated
protozoan infecting oysters, especially the haemocytes of C.virginica, C.gigas,
S.commercialis, Ostreola conchaphila and O.edulis (Schlicht and Mackin,
1968; Sprague, 1970).

Remarks

Although appreciable strides have been made on the oyster diseases in certain
European and western countries, information on this aspect with regard to the
Indian oysters is scanty. This is because, oysters are mostly exploited at
present in the country from the wild and they are yet to be farmed intensively.

Oyster Biology and Culture in India

Nevertheless, oyster culture is bound to develop soon on a large scale in view
of its great potential and its role in sea food production. It would, therefore, be
prudent that steps are taken now itself to initiate mission oriented research on
oyster diseases and cognate aspects of screening, monitoring, quarantining,
internal transmission of diseases and control measures, so as to ensure the
development of oyster culture on a sound and sustainable basis.

QUESTIONS

1. Give an account on oyster foulers, borers and predators. What are the
control measures?

2. Write on parasites and diseases of oysters.

3. Write short notes on: a) Barnacles, b) Boring sponges, c) Gastropod
predators of oysters, d) Larval vibriosis, e) Juvenile oyster disease,
1) Dermo disease, g) MSX disease, h) SSO disease.

Chapter 5

Fisheries

OYSTERS which abound the coastal and estuarine regions have been
considered as a prized food and fished by man in appreciation of their
delicate flavour since pre-Christian era. In addition to its flavour, oyster meat
is also considered to have medicinal properties. Hornell (1916) has observed
“The oyster meat is a tonic of the first order and a complete food, most
beneficial to weakned patients and those in whom appetite is deficient”. It has
been reported that the ancient Romans served large quantities of oysters at the
banquets and even used them as a monetary unit the denarius equal in value
to one oyster. Over the years the oyster stocks in several areas were overfished,
leading to the verge of extinction by intervention of mankind and by natural
disasters.

In India, currently the oyster fishery is a small scale activity at subsistence
level. Indian oyster meat is yet to make an entry into the international market.
However, oyster shell powder has been exported from India and in 2000, 1378
tonnes of shell powder, valued at Rs 4 million, was exported from the country
(MPEDA, 2000). In the last decade, oyster production by the harvest of wild
stocks has shown substantial increase. A brief description of the world oyster
fisheries, the fishing methods and the status of Indian oyster fisheries is given
in this chapter.

WORLD OYSTER PRODUCTION

The world oyster production by harvest from the natural beds during the
period 1994 to 2003 ranged between 1,58,187 tonnes in 1999 and 2,49,647
tonnes in 2000 with an average of 1,88,183 tonnes. In 2003, 1,99,517 tonnes
of oysters were landed. America was the foremost producer contributing 59.9
% of the landing followed by Mexico (24.9%) and Korea (10.1 %) (FAO,
2003a). A decline in the oyster fishery in some of the countries was witnessed
during this period. Thailand had contributed to the world oyster production
in the last decade but failed to make significant contribution in the subsequent
years. The principal geographic area which supports the oyster fishery is the
North-west and Western Central Atlantic Coast.

Crassostrea virginica singly contributed to more than three-fourths of the
global oyster landing during the year 2003. The production of this important
resource was mainly from America, Mexico and Canada. The second dominant

Table 20. World oyster production (in tonnes) during 1994 to 2003 (FAO, 2003a)

Oyster Biology and Culture in India

Is"

i —

Is"

1—

T -

Is""

co"

cm"

co"

■1 —

03"

T“

Is"

i —

Is"

i—

Is"

C\J

co"

1 —

cm"

Is""

LO"

i —

LO_

T—

io"

T—~

oo"

Is"

T—

T-

Is"

1 —

Is"

T-T

LO"

co"

Is""

03"

C\J

1—

cm"

■M"

Is"

"M-

1—

■i —

C\J~

cd"

cm"

co"

cm"

oo"

T-

^ _

1 _

■1 —

Is"

"4 —

LO"

''T

cm"

T—

cm"

•>-

cq.

T“

Is"

r"-

Is"

1—

T—

co"

cm"

LO"

Is"

■M"

ssl'

T-

oo"

co"

T-"'

io"

Is""

"sf

Is"

^ _

■'T

1"-

I —

T-

'r~

oo"

"'T

LO"

T- '

N-

1 _

Is-

Is"

1 —

Is"

T-

oo"

T—~

■'T

co"

T—

H — <
0
>4

-4 — ‘
0
>s

1—

C/3

0
-4— »
0
>4

0
■4— >
0
>
o

1—

\ _

0
-* — ‘
0

-4—'

* *

i _

"i_

'i_

■

0 ■

1 —

"3-

1s- ■

Is"

1 —

T”

cd"

Is"

1—

i —

•4—’

03 1

Is"

cm"

ID"

OO"

"■

LD 1

Is"

1™*

cm"

1—

co"

’■

03 1

Is"'

cm"

03"

cm"

Is"

CM 1

Is"

1 —

■M"

T-

Is""

03"

1—

T -

T—

■1 —

oo"

Is"

’’

1 —

oo"

03"

■4—

Is"

Is" CM

Is"

1 —

Is"

•, —

•4 —

■4— •

-4— ■

0 O

g Ql

Q. c

"0
+- >

-4 — 1

q[ 5

'-C CO

CL |-

C\J

Fisheries

species was C.gigas contributing to 10.8 % (21,536 tonnes) of the world
oyster landings. Korea was the major producer of C.gigas (20,201 tonnes)
followed by USA (1,225 tonnes). Rest of the production came from United
Kingdom-95 tonnes, France-8 tonnes, Equador-5 tonnes and Portugal-2 tonnes.
The mangrove oyster, C. rhizophorae was fished from Venezuela, Cuba and
Dominican Republic, the production being 4,197.2 tonnes. Several other
species of Crassostrea are fished commercially in south-east Asia and Brazil.
These are reported collectively in the FAO Fishery Statistics under the
designation Crassostrea spp. Details of the species wise landings during 1994
to 2003 are given in Table 20.

The group of flat oysters under the genus Ostrea, mainly O. edulis,
O.lurida, and O.chilensis formed < 5% of the landings. New Zealand, Ireland,
Denmark, United Kingdom and Turkey are the major producers of flat oysters.
Production of oysters under the genus Saccostrea was negligible. Though this
group is known to contribute to subsistence fishery in several South-east
Asian countries, it has not been documented.

The oyster production from Asia in 2003 was 20941 mt (10.5 % of the
world landing, the main contributors being Korea (96.4%), Indonesia(3.04%)
and the Philippines (0.48 %) (Table 21). Korea’s oyster fishery showed wide
fluctuations during the period 1994 to 2003. The production from Thailand
which was 1399 tonnes in 1989 was negligible during the subsequent years.
Among the oyster resources, Crassostrea gigas was the dominant species,
followed by C. iredalei. The oyster production from India is not reported to the
FAO.

OYSTER PRODUCTION IN INDIA

In India, oysters are fished and utilized in all the maritime states though the
magnitude of fishery and utilization is varied. Reports by Hornell (1910a,
1916, 1917, 1949), Rai (1928, 1932), Rao (1958, 1963, 1966, 1974), Jones
(1968), Alagarswami and Narasimham (1973), indicate that oyster fishing is
traditionally practiced by Indian coastal villagers since the last century. The
oyster production was low till the early 1990s, but since then it has improved.
The average annual landing of oysters during 1995 -99 is estimated as 18,800
tonnes (CMFRI, 2001). Based on the annual landings and the biomass estimated
through different planned surveys along the coastal regions of maritime states,
the potential yield of oysters was estimated as 33,962 tonnes (CMFRI, 2001)
indicating further scope to step up production.

The main fishing areas along the Indian coast, the species contributing to
the fishery and the resource utilisation pattern is given in Table 22. The
available information on oyster fishery is presented below.

North-east zone

Very little information is available on the oyster resources of West Bengal.

Oyster Biology and Culture in India

Oyster is locally known as ‘Kakada’ in Orissa. The main fishing area is the
Bahuda estuary in Ganjam district of Orissa. Oysters were fished even during
the pre-independence period. The fishery is mainly for the shell but live
oysters are also used by the local people. Since the late 80s the Department of
Mines leases out the fishing area annually instead of the Department of
Fisheries. During 1992-93 the lease amount realised was Rs 82,000 (Das,
1993). Annually about 1,500 tonnes of oysters are fished from this region.

South-east zone

The standing stock of oysters from this region (Andhra Pradesh, Tamil Nadu
and Pondicherry) has been estimated as 20,719 tonnes (Rao et al., 1996).
Though the oyster landings are not monitored, information collected during
the survey conducted by CMFRI has shown that the local fishers seasonally
exploit the oysters. Along the Andhra Pradesh coast oysters are fished from
Machilipatnam creek, Sarada estuary, Bhimunipatnam backwater, Upputeru
canal (Kakinada), Krishnapatnam and Gokulapalli. Tamil Nadu and Pondicherry
have the richest oyster resource in the country. In Ennore estuary and Pulicat
Lake, intense exploitation of oysters has been observed. The annual shell-on-
oyster production from Ennore estuary varied from 1062 to 71 15 tonnes (Rao
et al ., 1996). In Gadilam estuary the oyster meat is also used as bait in the hook
and line fishery. Rao et al. (1996) have indicated that oyster meat is collected
from Kovalam backwaters and supplied to Chennai city. The shrimp hatcheries
in this zone also use oyster meat as a feed for brood stock. There is only
limited exploitation of resources in most of the estuaries.

South-west zone

In all the three maritime states of this region viz. Kerala, Karnataka and Goa
oysters are fished mainly for their meat by the local fishers. In Kerala, well-
established oyster fishery has been reported in Korapuzha estuary,
Puthuponnani, Pozhikkara and in Ashtamudi Lake (Rao et al ., 1996; Kripa,
1998). During the last five years, oysters from Kerala were even marketed in
Maharashtra especially in Mumbai. The coastal villagers believe that oyster
meat is good for nursing mothers and also to people who suffer from
rheumatism.

In Kerala, the oyster fishery is influenced by several social and biological
factors. In most coastal villages, the number of fishers involved in oyster
fishing is highly variable. When there are more remunerative employment
opportunities in other fishing sectors such as trawling or fishing in the coastal
or near shore waters, the effort in oyster fishing declines considerably. The
market/consumer preference for other bivalve resources such as clams and
mussels in the same areas also affects the production. In Ashtamudi lake,
when the local fishing agents give indication of export order for the clam
Paphia malabarica, the traditional oyster fishers switch over to clam fishing.

Fisheries

Similarly when the oysters are in the spent or watery condition, the fishers
generally refrain from fishing resulting in low oyster catch. Preference for
land based occupation in the coastal villages, close to the developing urban
area, also affects the oyster fishery. The oysters are marketed in the nearby
villages either as shell-on oysters or as oyster meat. The price in Kerala ranges
from Rs 40/- to 45/- for 100 no. of shell-on oysters (Rao et al., 1996; Kripa,
1998).

North-west zone

During the early part of last century, oysters were plenty in the estuaries of
Maharashtra. These were fished by the local people and marketed at various
places in the state (Alagarswami and Narasimham, 1973; Rao, 1974). However,
in recent years due to deteriorating water quality of the oyster beds near
Mumbai the production has declined (Sundaram, 1988). In Gujarat, oyster
fishery is of a very low magnitude and Chhaya et al (1993) have reported that
the resource is so sparse that no fishery can be developed based on the
available stock.

OYSTER FISHING METHODS

Because of the sedentary habit of oysters, the main fishing gears used are
simple (Korringa, 1952). In the temperate countries, oysters are fished by
simple gears such as rakes and tongs. In some areas they are just hand picked
during low tide from shallow areas. Rakes have long handles and long,
slightly curved teeth. Raking is done by hand in sloping oyster beds upto 8 m
depth. Tongs are hand operated and used on level bottoms usually upto 5 m
depth. Tongs consist of a pair of rakes attached to long wooden scissor-like
handles which are joined approximately one-third of the distance from the end
of rakes. The teeth of the rakes point inward and some tongs have baskets
attached to both ends. With a series of short lifting movements, the oysters are
scraped off the bottom. Tonging is a time consuming operation and can be
done only when the water is calm. Patent tongs are also used for fishing
oysters. The metal part is similar to that of hand tong, they are hinged so that
they open, as they are lowered and close when lifted. Another oyster fishing
method of fairly recent origin is dredging. The dredge or the drag is a large
rake-head backed with a bag attached to a strong rope in place of a handle. It
is usually used for harvesting oysters in deeper areas and is towed over the
bottom by a powered boat and hoisted either by a mechanical or motor-driven
force. Dredging is considered harmful to the ecosystem and is not usually
permitted.

After fishing the oysters are usually culled (separated) by a culling
hammer. The hammer usually has a measuring gauge and undersized oysters
and empty shells are returned to the oyster beds. Predators such as starfish and
rock crabs, taken incidentally are also destroyed. In the Chesapeake Bay, the

Oyster Biology and Culture in India

Table 22. Important fishing areas along the Indian coast and the utilization of oysters

State

Resource

Main Fishing areas

Utilization

Orissa1

Bahudi estuary near Sonapur
and at the mouth of the

Chilka Lake

Cement industries
and poultry feed.

Andhra

Pradesh2

Sarada estuary, Bhimuni-
patnam backwater, Upputeru
canal (Kakinada) Krishna-
patnam and Gokulapalli

Cement industries;
shrimp feed.

Tamil Nadu
and

Pondicherry3

Gokulapalli, Ennore, Muthupet
swamps Killai backwater,
Pazhayar, Vaigai and
Tambaraparni estuaries,

Pulicat and at T uticorin

Cement industries;
shrimp feed; human
consumption.

Kerala3

Cm, Sc

Korapuzha estuary, Ashtamudi
and Vembanad Lakes,

Cochin backwaters, estuaries
and the creeks of Dharmadam,
Valapatnam, Nileswaram and
Chandragiri

Human consumption;
Cement industry.

Karnataka2

Nethravathi, Mulki, Udayavara,
Venkatapur, Coondapoor and
Kali estuaries

Human consumption;
Cement industry.

Goa4

Cm, Cg,

Ribander, Siolim, Curca

Human consumption;
Cement industry.

Maharashtra4

Cg,

Alibag,Ratnagiri,Jaytapur,

Malad, Boisar, Satpuri,

Palghar, Kelwa

Human consumption;
Cement industry.

Gujarat5

Sikka

Cement industry.

Andamans2

Port Blair, Havelock Island,
Mayabunder and Dighlipur

Human consumption.

Source : 1-Das, (1993); 2-James and Narasinham, (1993); 3-Rao eta!., (1996); 4-
Alagarswami and Narasimham, (1973); 5-Chhaya eta!., (1993)

Cg : C.gryphoides ; Cm : C.madrasensis; Sc : S.cucullata

oysters are fished by all the gears mentioned above. Conflict between
mechanized and non-mechanized fishing gear operation is also seen in oyster
fishery. In North America, disagreement between the tongers and dredgers
became so fierce and bloody that it was called ‘Oyster war’. In 1868, the
Maryland Oyster Navy, a special police force, was established to bring law
and order to the Chesapeake Bay and Potomac River. These oyster wars came
to a formal end only when laws were passed by the Government in 1962
indicating when and where the dredgers could work. In India, the main fishing
method is by hand picking or by detaching the oyster clumps with a chisel or

Fisheries

knife. Mechanical dredging as seen in some parts of the temperate countries
is not practiced in India.

FISHING SEASON AND SPECIES COMPOSITION

Oysters are fished throughout the year along the west coast except during the
peak monsoon period. The fishers themselves are good judges of the oyster
quality and have good knowledge of the period during which the oyster meat
is watery. In some estuaries like the Vembanad Lake in Kerala, oyster fishermen
change the fishing grounds based on season. They pick the oysters from the
deeper areas like the seaward navigation channels during the monsoon, since
the intertidal population will be mainly dead oyster shells or those live will be
of very poor quality (Kripa, personal observation). Along the north-west
coast, in the creeks of Maharashtra the oysters are fished by diving, the peak
fishing season being November-December. In these regions also the effort and
number of fishing days are found to have wide monthly variation (Alagarswami
and Narasimham, 1973).

In most estuaries or open coastal regions, the larger Crassostrea spp. and
the smaller Saccostrea cucullata contribute to the fishery (Rao et al., 1996;
Kripa, 1998). In Ashtamudi Lake, 92% of the oysters landed are C.madrasensis,
the rest being S. cucullata. In Vembanad Lake and in the estuaries of north
Kerala, C. madrasensis contributes to more than 98% of the catch. This is
mainly because the fishing grounds are more in the brackishwater region than
in the marine region, and C. madrasensis population thrives well in
brakishwater. The catch per person ranges from 20 to 40 kg /day. During 1994
-1995, the peak fishing season was observed during the premonsoon period,
March to May, when the monthly landing was estimated as 7 tonnes. The
lowest of 1.6 tonnes was in August. From September to January, the fishery
progressed steadily from 2.4 to 6.3 tonnes. During June - July, the landings
were low (Kripa, 1998).

SIZE AND AGE COMPOSITION

In most estuaries of Kerala, only oysters above 50 mm are harvested. Smaller
oysters of length range 35 to 50 mm are culled and left in the subtidal region,
which later reach harvestable size. The fishery in Ashtamudi Lake is mainly
supported by C. madrasensis of 70 to 90 mm and S. cucullata of 30 to 50 mm.
Oysters targeted to metro hotels are usually above 70 mm while for the local
markets smaller oysters are also included. The length range of oysters in the
natural bed in some of the major oyster beds is given in Chapter 2.

Oyster fishery is comparatively of a smaller magnitude when compared
to clam fisheries. The population characters of S. cucullata in Ashtamudi Lake
have been studied by Kripa (1998). By the Response Surface Analysis and the
Automatic Search Routine, the La was estimated as 61.5 mm and K at 0.89

Oyster Biology and Culture in India

per month. The study indicated that the oysters have a life span of 3 to 5 years
and they grow to 36.2, 51.1 and 57.2 at the end of 1 , 2 and 3 years respectively.
The fishing mortality in Ashtamudi Lake is comparatively higher when
compared to the almost negligible values in the oyster beds near Worli in
Maharashtra. But the high density has been found to restrict the space available
for growth at these sites.

The length at first capture Lc of S.cucullata was 32 mm, since it was
observed that this is the smallest size group fully represented in the catch. The
instantaneous rate of total mortality Z was estimated as 2.15 using the length
converted catch curve. The natural mortality M was estimated as 0.87 and the
fishing mortality F 1.28. The various parameters of S.cucullata population in
Ashtamudi Lake are given in Table 23. The exploitation ratio U was 0.59.
The yield Y was estimated as 4.53 tonnes which is the average of the annual
catch during 1994 - 96. Applying the values of Y and U, the total annual stock
was estimated as 7.68 tonnes and the average annual biomass as 3.54 tonnes.

Table 23. The population and fishery parameters estimated for S.cucullata in Ashtamudi
Lake, Kerala.

Y (tonnes)

Y/U (tonnes)

Y/F(tonnes)

2.15

0.87

1.28

0.59

4.53

7.68

3.54

Tr(yr)

Tc (yr)

Tmax (yr)

Lmax (mm)

Wmax (g)

10 mm

32 mm

0.4

0.7

3.4 yrs

58.2

48.13

Source : Kripa (1998)

SUBSOIL SHELL DEPOSITS

C. madrasensis shell deposits along the south-east coast are fished and used
as raw material in fertilizer, calcium carbide, lime, cement and poultry feed
industries. The main fishing areas are Bahuda estuary in Orissa and Ennore
estuary in Tamil Nadu. Apart from this the subsoil shells are fished in several
estuaries along the east coast. Mahadevan (1987) has reported that the mining
of subsoil deposits by lessees in estuaries like Kali River, Athankarai and
Bahuda river yield nearly 15,000 tonnes of shells annually.

In Orissa, the Government used to lease out the oyster beds and the
harvested shells are utilized for manufacturing poultry feed (Alagarswami and
Narasimham, 1973). More recently Das (1993) has reported that annually
about 1,500 tonnes of oysters are exploited from the Bahuda estuary. In
Ennore estuary, Alambaru estuary and Kovalam backwaters, the subsoil deposits
are collected in large quantities. In Kovalam backwaters, once in four years
about 80 % of the oysters are removed for manufacture of lime which is used
in building construction (Rao et al ., 1996). Rao et al. (1987) described the
fishery and exploitation of molluscan shell deposits along the Pinnakayal -

Fisheries

Valinokkam coast. At Mariyar and Valinokkam, the shell deposits of the clam
M. casta (94%) and C.madrasensis (6%) occur at a depth of 0.2 to 1.0 m.
These deposits are of recent origin. Many of these areas were taken on lease
by salt companies for construction of salt pans. The loosely occurring shells
of 40-180 mm length are removed by digging and hand picking. At Kovangad,
the shell deposits are at about 0.5 m below the water surface and are about 2.0
m thick. Here also, the fishing method is manual by pushing rectangular
wooden panels into the earth, removing the mud and sand present inside and
collecting the shell. This is done by marginal agriculture farmers, when they
do not have work in the fields. The State Government leases out the exploitation
right to different individuals who employ the farmers. The annual production
has been reported to range between 300 and 400 tonnes. Fishing is done
throughout the year except in the north-east monsoon months (October to
December).

In the Gulf of Kutch, regular exploitation of both lime and oyster shells
was done by a cement industry in Sikka which had obtained long term lease
for lifting the sand. This has led to drastic decline in oyster population
(Chhaya et al., 1993).

MANAGEMENT OF OYSTER FISHERY

Oyster production from natural beds has shown wide fluctuation during the
last one and half centuries. Severe depletion of stocks in the major oyster beds
either due to overfishing, disease outbreak or environmental degradation has
been reported (Sinderman, 1990; Carlton and Mann, 1996). In some areas a
combination of one or two of these factors were implicated (Rothschild et al.,
1994)

In Europe, commercial exploitation of oysters over the years has led to
virtual destruction of natural resources. The flat oyster beds were repeatedly
closed for fishery due to overfishing and stock depletion in Germany, Denmark
and Netherlands (Schlauch, 1999). Another typical example of overfishing
and resource mismanagement is the oyster fishery of Willapa Bay in North
America. Due to the development of shipping industry, the oyster landings
increased to 13,000 mt in 1890. Then they declined rapidly to a level of less
than 5,000 tonnes in 1920. Parasites and diseases were considered as responsible
for the collapse of the fishery. (More details are given in Chapter 4.) The bluff
oyster ( Tiostrea chilensis ) fishery in New Zealand collapsed in the mid-late
1980’s due to Haplosporidian Bonamia sp. (Keogh et al., 1997). Apart from
this, industrialization and deterioration of water quality have also contributed
to the destruction of oyster beds such as the oyster industry in south Puget
which flourished during the 1920’s and dwindled due to pollution from a
paper and pulp mill. Historically one of the best recorded oyster industry is
that of Chesapeake Bay which peaked at 6,15,000 tonnes in 1884, declined to

Oyster Biology and Culture in India

about 12,000 tonnes in 1992 mainly due to environmental degradation, fishing
pressure and disease outbreaks (Rothschild et al., 1994; Harding and Mann,
1999). Thus areas which were once famous for oyster production became
shadows of their past.

In an effort to revive the natural oyster fishery, attempts were made to
transplant or introduce either C.gigas or C.virginica and these were partly
successful (Beattio et al., 1982). In some regions they failed to establish self
reproducing populations. In addition to these transplantations, regulations and
programmes based on the inferences drawn from the ecobiological research,
projects on oysters were formulated, and these were strictly enforced. The
results were encouraging proving that by appropriate regulations the natural
resources can be protected.

Rothschild et al. (1994) have attributed the cause for long - term decline
of oyster to habitat loss associated with intense fishing pressure. To effect the
recovery of the ailing Chesapeake Bay oyster stock, a 4-point management
strategy was prepared by the authors.

• Fishery management steps to control size specific fishing mortality.

• Repletion strategy - a) Placing shell on existing substrate to effect
habitat replacement, increase the growth and survivorship of oysters,
b) Transplanting recruited spat into areas of improved growth and
survivorship.

• Habitat replacement strategy - building new substrate to create
additional suitable oyster habitat for recruitment of spat, growth and
survivorship of new recruits. As it takes decades to create an oyster
reef naturally, engineering replacement habitat with artificial structures
in optimum growth and survival areas seems to represent a viable
alternative.

• A broodstock sanctuary - would include the designation of ‘no - fishing’
restriction in specific areas where production of larvae and spat
settlement are known to be high.

In an effort to restore native oysters in Chesapeake Bay, citizen volunteers
are involved in a unique partnership with Government management agencies.
In 1996, these volunteers helped to transplant approximately 7,50,000 large
wild caught oysters onto a one acre broodstock sanctuary. Spawning by these
oysters resulted in a 10 to 200 fold increase in juvenile abundance in 1997
(Braumbaugh et al., 1998). This growing consciousness among the people
about the need to regulate fishing, increase of oyster habitat and provide
broodstock sanctuary is a positive sign pointing towards a sustained fishery for
the future. Fishery management measures curtailing fishing activity during the
breeding season has been in vogue in the USA for the last two decades. For C.
virginica, in Chesapeake Bay, the minimum size of capture was regulated to 76
mm in 1990. An interactive relationship has been observed between the

Fisheries

reproductive behaviour, fishery and the population equilibrium of C. virginica.
This oyster is weakly protandric hermaphrodite, i.e. some older males become
females. (Galfstoff, 1964; Kennedy, 1983). When the fishing pressures on such
population increases (i.e, decline in female proportion) the production of eggs
per adult biomass (spawning efficiency per unit biomass) is reduced much
more than in a non hermaphroditic population. Rothschild et al. (1994) have
critically analyzed the causes for the decline in Chesapeake Bay oyster population
and have commented that an increase in size of first capture to 122 mm would
be able to double the yield per recruit and quintuple the spawning stock
biomass. This would be more effective than decreasing the fishing pressure.

Another typical example where management measures have helped revival
of fishery is at Long Island Sound. Oyster production from this region rose
from 85 tonnes of meat in the 1960s to 1000 tonnes in 1975 (Mackenzie,
1989). This 10-fold increase in production resulted as the oyster companies
increased the planting of oyster shells on the beds from 6,200 m3 to about
8,000 m3 in a year and by controlling mortalities of seed oysters from predation
by gastropods and suffocation by silt. The gastropod predators were removed
by suction dredges and starfishes by catching them with mops or by killing
them with granulated quicklime. Mortality due to siltation was avoided by
placing them when the spat were less active (Mackenzie, 1981).

In India, though the oyster beds are extensive the demand for oyster meat
is low and hence their exploitation is by and large remaining at a low level
except at a few places. This low level of exploitation has not necessitated
formulation of management measures regulating fishing activity. To increase
the utilization of this resource, management measures should be directed
towards developing proper marketing channels. Quality assurance to consumers
along with wide ranging awareness campaigns about the nutritive value of
oysters is urgently required. This leads to demand driven fishing effort,
resulting in increased production from the currently under exploited resources.

Chhaya et al. (1993) have indicated that the oyster fishery cannot be
developed in the existing oyster beds in Gujarat owing to the very thin oyster
densities (< one number/ m2). The slow growth of the local oyster species
( C.gryphoides ) also does not contribute to the growth of oyster stock. With the
objective of developing the oyster resource of Gujarat, the faster growing
C.madrasensis spat produced in CMFRI hatchery in Tuticorin was transported
by road and air to Jamnagar within a transit period of 36 hrs. Though the first
trial in 1988 was not successful, the second consignment of 5,500 oyster spat
of 10 mm length showed more than 90% survival during transportation. The
spat grown in cages in the intertidal region showed a growth of 2.9 cm in one
year. This growth rate of C.madrasensis reared in cages is far from satisfactory.
However further studies are needed to evaluate the performance of
C.madrasensis in this region.

Oyster Biology and Culture in India

Intense exploitation has been reported at Ennore estuary, Pulicat Lake,
Kovalam and Korapuzha estuary. Rao et al. (1996) have suggested that the
heavy exploitation of live oysters from Ennore and Kovalam should be
regulated. It was also observed that the density of spat was very low in most
of the estuaries. Measures have to be taken to increase the spat fall in areas
where oysters are regularly fished. From the foregoing brief account the
management measures required to develop a sustainable oyster fishery in the
country are:

• Market development of oyster meat by creating awareness about the
nutritive value of oyster.

• Quality assurance to the consumer by making depuration of fished
oysters mandatory and also pollution monitoring of waters in areas
where oysters are regularly fished.

• Fishery restriction in areas of intense exploitation.

• Placing additional empty shells (shelling) for increasing the spat
settlement in areas where commercial fishery exists.

Development of oyster culture in areas suitable for augmenting production.

QUESTIONS

1. Describe oyster fishing methods, season and species.

2. What are the strategies for the recovery of oyster fisheries?

3. Write on oyster production, important species in the world and in India.

Chapter 6

Seed Production

THROUGHOUT the world natural spat collection forms the basis of most
oyster culture industries. Along the Pacific North-west USA coast, hatchery
produced seed are used in the cultivation of the Pacific oyster, Crassostrea
gigas. Natural seed collection is cheaper when compared to the cost of seed
produced in the hatchery.

NATURAL SPAT COLLECTION

The substrate provided to the oyster larvae for attachment is known as cultch
or collector. It should be clean and hard. In the temperate waters, oyster or
scallop shell is widely used as cultch. More recently tubular plastic mesh
(Netlon) is used for packing shell cultch. Quayle and Newkirk (1989) have
stated that roughened surfaces appear to be more suitable for spat settlement,
the colour of the cultch has no significant influence on the setting behaviour
of the oyster larvae and that the presence of a bacterial film on the cultch for
the setting of the eyed larvae is not essential, at least for the genus Crassostrea.
They have also stated that the larvae tend to settle more readily on surfaces on
which there are already some spat.

The selection of the cultch material depends upon the type of culture. For
example, in the production of individual oysters (unattached) for the half-shell
market, lime-coated tiles give good results as it is easy to remove the oyster
spat from the tiles for further rearing. For the ren method of culture, strings
made of oyster shells with spacers inserted between the shells are hung usually
from racks. The grow out culture is often carried by using the same rens. For
the stake culture the common method is to drive the bamboo or the wooden
poles (stakes) into the substratum and the stakes act as spat collectors; the
grow out culture is carried on the same stake. For the on-bottom oyster culture,
oyster shells, stones, and concrete panels laid in the shape of inverted ‘V’ on
the substratum are some of the materials used as cultch.

It is necessary to have a good knowledge about the biology of the oyster,
particularly on reproduction for the collection of spat. Laying the cultch in the
water at appropriate time is critical for successful spat collection. There are
four methods to predict the time of spatfall (Nair et al., 1993) namely, study
of gonad maturity stages, eyed larval counts from the plankton samples,
regular examination of test panels or cultch materials held in the spat collection

Oyster Biology and Culture in India

areas, and observations on the locally occurring substrates for oyster spat.
Successful spawning, as determined by gonadal studies, need not necessarily
result in good spat settlement because of unfavourable conditions such as
heavy silt load, hyper or hyposalinity, and drift of the larvae by water currents
away from the area of spat collectors. Spatfall forecast based on the abundance
of eyed larvae in the plankton has its own drawbacks. It is extremely tedious
(Clarke et al, 1991) as it involves sorting of oyster larvae from large number
of the larvae of other groups of animals and more importantly the difficulty in
the identification of the oyster larvae. Quayle and Newkirk (1989) stated-
identification of bivalve larvae is one of the more difficult aspects of shell-fish
biology to master. Use of test panels made of glass, commonly experimented
in biofouling studies or cultch materials such as oyster shells hung at different
places and depths is perhaps the best method for oyster spatfall prediction in
the tropical waters. Observations on the occurrence of spatfall on the locally
available substrates which include oyster shells, submerged rocks, fish traps,
cage floats, piers etc. can be an effective indicator for suspending cultch.
However, spat size should be < 2 mm to indicate recent spawning (Nair et al.,
1993).

NATURAL SPAT COLLECTION IN INDIA

Several studies have been conducted to determine the availability, duration
and intensity of the spatfall of oysters from Indian coastal waters.

Crassostrea madrasensis

The cultch materials used include oyster, mussel, windowpane oyster and
coconut shells, asbestos sheets, roofing tiles, velon screens, polyethylene liner
sheets, PVC tubes, wood pieces, concrete pieces and slabs, bamboo frames,
automobile tyres and close meshed plastic buckets. Thangavelu and Sundaram
(1983) described the process followed in giving lime coating to tiles. After an
initial coating of lime, a secondary coating, comprising 3:4 ratio of lime and
fine sand mixture is given to the tiles (Figure 1 3). Several authors (Thangavelu
and Sundaram, 1983; Muthiah, 1987; Sarvesan et al, 1990; Patterson and
Ayyakkannu, 1997) reported that in the cultch laid horizontally, the lower
concave surface received more spatfall than the upper convex surface. Sarvesan
et al. (1990) stated that 71 % of spat was set on the lower concave side and
the rest on the upper convex side. Silas et al. (1982) mentioned the spat
settlement ratio as 1:5 on the upper convex and lower concave surfaces
respectively. This disparity is generally attributed to silt deposition on the
upper surface which is not conducive to spatfall (Quayle and Newkirk, 1989).

Thangavelu (1988) stated that in the Pulicat Lake, the veliger larval
abundance was high in November 1980 but the spatfall was poor, while in
April 1981, the larval abundance was less than moderate but the spatfall was
high. He further stated that the low salinity of 0.37 ppt in November 1980

Seed Production

Fig. 1 7. Lime-coated tiles in trays held on racks in the T uticorin Bay for oyster spat
collection. Courtesy: CM FR I, Cochin, Kerala

would have affected the survival of the larvae resulting in low spatfall and the
high salinity of 34.83 ppt in April 1981 would have resulted in successful spat
setting. This study highlights the difficulties faced in spatfall prediction based
on larval abundance. Kripa and Salih (1999 a) mentioned that in the Ashtamudi
Lake the spatfall observed in May is prone to mortality due to dilution of water
caused by the monsoon in the following months.

From Table 24 it is obvious that biannual spatfall is more common and
was observed in the Bheemunipatnam backwaters, Pulicat Lake, Muthukadu
backwaters, Vellar estuary, Athankarai, Tuticorin bay and the Mulki estuary.
At a given centre between the two seasons, one is marked consistently with
high intensity spatfall than the other. In general, March - April and October -
December are the seasons of spatfall for C. madrasensis (Table 24).

Spatfall throughout the year or for the major part of the year was
observed at Bheemunipatnam, Kakinada, Athankarai and the Ashtamudi areas.

At Tuticorin and Ashtamudi, spat collections on oyster shell rens were
made continuously for 5 years or more (Figure 1 8). The average spat settlement
at Tuticorin was 5.8 to 7 nos/ oyster shell and at Ashtamudi it was > 23 nos/
oyster shell. This indicates that the Ashtamudi Lake is highly productive for
spat collection. In fact the abundance of seed and the demonstration of the
oyster farming technology by the CMFRI scientists in the Ashtamudi Lake

Oyster Biology and Culture in India

Table 24. Spat collection of C. madrasensis along the Indian coast

Area of study

Spatfall particulars

Author

Andhra Pradesh

Bheemunipatnam

Throughout the year. Peaks in March
and October. Close meshed plastic
buckets 4-50 nos/ 10 cm2. In October-
December 79 intense spat fall of

100-200 nos/ 10 cm2 occurred.

Reuben et al.,
1983.

Kakinada Bay

March-September.

Rao et al., 1994.

Tamil Nadu

Adayar estuary

November-January/ February.

Rao and Nayar,
1956.

Pulicat Lake

Peak October-December with average of

4.7 nos/ 100 cm2. Secondary settlement
March-April with 0.29 nos/ 100 cm2.

Ramakrishna,

1988.

Pulicat Lake

Spat settlement high in May and low in
November. Veliger larvae abundance
in plankton coincided with high spatfall.

Thangavelu, 1988.

Muthukadu

Peak September-November and low

Sarvesan et al.,

backwaters

intensity in February-April. Other months
no spatfall. Spat 8-109 nos (average 55/tile).

1990.

Vellar estuary

Peak in August-September and minor
peak in April-May, lime coated tiles most
efficient. Average density 21 .4 nos
at 80 cm depth and 54.2 nos at 100 cm
depth per tile (1 1 x 3.8 cm).

Patterson and
Ayyakkannu, 1997.

Athankari estuary

Major spatfall in January-April; minor
June-December, Average 0.2 nos/
oyster shell.

Rao et al., 1983.

Karapad creek

April-May. Up to lOOnos/tile.

Nayar and

(Tuticorin)

Average 40 nos/ tile of 24 x 15 cm.

Total 6,00,000 spat collected in 45 days.

Mahadevan, 1983.

Tuticorin

Intense March-April, less intense
September-October. Maximum

105 nos/ tile of 20 x 12 cm.

Maximum 517 nos/ corrugated
asbestos sheet of 30 x 30 cm.

Average 393 nos/ sheet.

Thangavelu and
Sundaram, 1983.

Tuticorin

Major April-May, secondary August-
September. In 1979 Tuticorin Bay

316 nos/ m2, 76 nos/m2 in Karapad
creek, and 92 nos/m2 in natural bed on
lime coated tiles of 24 x 15 cm. In

1980 average spatfall: 7 nos/ oyster
shell, 5 nos/ mussel shell, 1 no/ coconut
shell, 4 nos/ asbestos sheet of

120 x 80 cm, 87 nos/ velon screen of

4.25 x 16.5 cm, 215 nos/ polythene lined
sheet of 4.25 x 16.5 cm, 30 nos/ PVC

Muthiah, 1987.

Seed Production

Area of study

Spatfall particulars

Author

tube of 30 cm diametre and 1 m length
and 33.5 nos/ tile of 24 x 15 cm size.

During 1981 through 1984, spat settlement
of 12, 15.6, 29 and 15 nos/ tile of

24x15 cm. Average spatfall ranged from

5.8 to 6.5 nos/ oyster shell.

Kerala

Ashtamudi Lake

During October 1993-September

1994 spatfall 10 months except in

June and September. Peak December-
January. Average 24.6 nos/ oyster shell.

Velayudhan etal.,
1995.

Ashtamudi Lake

In December 1994-February 1995,
average spatfall 24 nos/ oyster shell.

Velayudhan etal.,
1998.

Ashtamudi Lake

At bar m-outh and estuary throughout
the year. Intense during November-
January at both sites. Minor peak in May.
From June to August negligible spat
settlement. Maximum settlement

35 nos/ test panel of 20 cm x 20 cm.

Kripa and Salih,
1999 a.

Cochin

backwaters

January-February.

Purushan et al.,
1983.

Karnataka

Mulki estuary

Peak November-December;
minor March-April.

Joseph and

Joseph, 1983.

Fig. 18. Oyster strings suspended from a rack for natural spat collection in the
Ashtamudi Lake. Note the strings are closely set
Courtesy: CMFRI, Cochin, Kerala

Oyster Biology and Culture in India

resulted, for the first time in India, in the emergence of commercial oyster
farming by the villagers.

Crassostrea gryphoides

In the Kelawa backwaters near Mumbai spatfall begins in July and extends till
September (Durve and Bal, 1962).

Saccostrea cucullata

Along the Bombay (now Mumbai) coast, Awati and Rai (1931) observed spat
settlement throughout the year except during the monsoon (mid June-
September). Joseph and Joseph (1983) stated that the spat settlement in the
Mulki estuary is heavy throughout the year except during July-August
(monsoon). In a brief study during January - March 1986 near Mumbai,
Sundaram (1988) observed the occurrence of spat during these three months.
In the Ashtamudi Lake, Kripa and Salih (1999 b) monitored the spatfall on test
panels of 20 x 20 cm size. They observed spatfall throughout the year and at
the bar mouth this species dominated (81.7 %) of the total oyster spat. The
density on the test panel varied from 258 in February to 43 spat in September.

S. cucullata generally occurs along the open coast and close to the mouth
of the estuaries where salinity variations are in a narrow range. The studies
indicate the spatfall throughout the year.

SEED PRODUCTION IN THE HATCHERY

Attempts to raise oyster seed under controlled conditions were made towards
the end of the 19th century. Brooks (1880) studied the eggs and early larval
stages of the American oyster Crassostrea virginica. Wells (1926, 1927)
succeeded in rearing the larvae of C. virginica to spat in glass jars. The earlier
workers failed in their attempts in larval rearing and spat production mainly
due to the poor quality of the seawater used and for not providing suitable
micro algae as food. Since 1950’s, Loosanoff and Davis (1952a,b; 1963),
Walne (1956, 1974), AQUACOP (1977), and Dupuy et al. (1977) have
standardised the oyster seed production technology in hatcheries. This
development has paved the way not only for the commercial production of
oyster seed for oyster culture but also for researches in oyster genetics.

The selection of suitable site for oyster hatchery is of utmost importance
and many factors are to be taken into consideration. Uninterrupted supply of
good quality seawater, free from industrial and sewage pollution is required.
The suspended particles and silt load in the water should be low. Sites close
to river mouths should be avoided, since during monsoon, flooding dilutes the
seawater salinity, rendering it unsuitable for seed production. It is advantageous
to select a site which is close to the oyster farm and natural oyster beds. The
site should be easily accessible for the transport of men and materials throughout
the year.

Seed Production

HATCHERY PRODUCTION OF OYSTER SEED IN INDIA

In India the larvae of C. madrasensis were reared in the laboratory up to the
straight- hinge stage by Samuel ( 1 983) while Rao ( 1 983) succeeded in inducing
spawning and rearing the larvae till settlement. A breakthrough in the induction
of spawning, larval rearing and mass production of C. madrasensis spat was
achieved by Nayar et al, (1982, 1984) at the Shellfish Hatchery of the CMFRI,
Tuticorin. The various stages in the oyster seed production were standardised
by Nayar etal. (1987 b, 1988 b) and Rao etal. (1992). The hatchery operations
are divided into five phases namely, selection and conditioning of broodstock,
induced spawning, fertilisation and early development, larval rearing, preparation

of cultch materials and production of spat, and culture of algal food.

Hatchery Facility at Thticorin

Building: The main hatchery complex is a 15 x 10 m shed, half of which
is roofed with translucent FRP sheets and the other half with asbestos sheet.
Air vents, exhaust fans and glass-panelled large windows are provided. Concrete
flooring is given and a pair of closed drains run along the entire length of the
hatchery to collect the water drained from the rearing tanks. In the asbestos
roofed section are provided four identical rooms of 4 x 2.5 m size for
microalgae culture, broodstock conditioning, duty room and analytical
laboratory. The translucent portion of the hatchery is used for larval/spat
rearing and mixed algal food production. The algal culture and broodstock
conditioning rooms have thermocool ceiling and are air conditioned.

Seawater Supply: It comprises an intake point, a draw well, sedimentation
tanks, filter bed, water sump, overhead tank and delivery lines to the hatchery
(Figure 19). Seawater is drawn into the well through a 15 cm diameter PVC
pipe by gravity and is pumped by 1 HP pump set to the sedimentation tanks
where large particles in the water settle. The supernatant water is passed into
the filter bed. The latter consists of river sand at the top followed by charcoal,
pebbles and finally small granite stones at the bottom. It effectively filters
particles above 10-20 pm (Nayar et al 1984). The filtered seawater is collected
in a storage sump (capacity 20,000 1) and is pumped by 7.5 HP pump to
overhead tank (capacity 10,000 1). Standby pumps are kept for emergency.
Water is drawn to the hatchery from the overhead tank through 12 mm
diameter PVC pipes. The receiving end in the hatchery is plugged by surgical
cotton to prevent still smaller particles from entering into the rearing tanks.
This facility can supply 10,000 1 filtered seawater daily to the hatchery. The
nannoplankters up to 10 pm are passed into the rearing tanks in the hatchery.
Recently high pressure mechanical filter was installed in the hatchery which
facilitates effective filtration. The annual variation of the water temperature is
from 23.5-32.6° C, salinity 34.11 to 36.32 ppt and pH 7.76 to 8.20 (Nayar et
al., 1987 b).

Oyster Biology and Culture in India

Fig. 1 9. Schematic diagram of oyster hatchery of CMFRI at T uticorin. 1 . Seawater
intake pipe 2. Draw well 3. Sedimentation tank 4.Filter bed 5. Storage sump
6. Overhead tank 7. Seawater supply pipe to hatchery 8. Generator 9. Air
Compressor 10-19. Larval rearing tanks 20-29. Spat rearing tanks 30-33.
Algae culture tanks 34. Spawning tanks 35. Analytical room 36. Duty room
37. Stores 38. Conditioning room 39. Axenic algae culture room 40. Drain;
AC- Airconditioner D- Door

Air Supply System: This consists of air compressors, filters, PVC air grid,
polythene aeration tubes, diffusion stones and air regulators. Air compressor

Seed Production

of rotary vane model with attached storage tank and run with 1 HP electric
motor is used. The air flow is regulated and passed through a series of filters
to remove oil and moisture. Air is supplied to the rearing tanks through 25 mm
diameter PVC pipes. Air is drawn at the required places from the pipe lines
through nozzles fixed to the pipes. Air is supplied to the tanks through
polythene tubes and diffuser stones. Air supply to the tanks can be adjusted
with the help of a gate valve connected to the polythene tubes. A standby
compressor helps in effective management of air supply to the hatchery.

Generator: A generator of 10 KVA, operated by a 16 HP diesel motor is
installed for use in case of interruption in the power supply.

Rearing Tanks: The rearing tanks comprise FRP tanks of 75 x 50 x 25 cm
for conditioning the oysters, one 100 1 capacity perspex tank for spawning the
oysters, 20 FRP tanks of size 200 x 100 x 50 cm for rearing larvae and spat
(Figure 20), four FRP tanks of 200 x 100 x 50 cm for outdoor algae culture
and five perspex tanks of 100 1 capacity for indoor algal culture.

Other Equipments: Sieves of different mesh sizes, compound microscope,
haemocytometer, plankton counting chamber, pH meter, thermometers,
salinometer, oxygen analyser, autoclave, glassware and plasticware.

Selection and Conditioning of Broodstock

The word conditioning is used to denote the process by which the gonad
maturation of the oysters is hastened so that the gametes become ripe for
spawning. The process involves manipulation of environmental conditions

Fig. 20. Oyster hatchery at Tuticorin showing the larval and spat rearing tanks
Courtesy: CMFRI, Cochin, Kerala

100

Oyster Biology and Culture in India

and nutrition. In temperate countries, the spawning season of bivalves is of
short duration, limited to about 3 months. During the non-spawning period the
maturity process is accelerated in the hatchery by keeping the bivalves at
elevated temperatures with suitable food. During the summer, holding the
mature bivalves at lower temperatures prevents spawning. Thus by conditioning,
bivalves in ripe condition can be made available for most of the year (Loosanoff
and Davis, 1963; Dupuy et al., 1977).

In India conditioning the oysters about 5° C below the ambient water
temperature with suitable algal diets accelerated the gonad development,
resulting in sexually ripe oysters. The oysters are selected based on the
condition factor and age. Selection of a mixed and heterogeneous stock of
oysters from several areas will give better results. It is also desirable that the
salinity regime of the area from where the oysters were collected is comparable
to that of the water salinity in the hatchery. Otherwise the oysters should be
acclimatised before they are conditioned. The prevailing temperature of the
collection area is recorded since, based on this manipulation of temperature it
is effected for conditioning the oysters.

C. madrasensis of the length range 60-90 mm are considered as ideal and
it is preferable that 30 % of them belong to ‘O’ age group (60-75 mm) in order
to be assured about the presence of males in the broodstock (Nayar et al.,
1987b). The maturity stage of oysters is ascertained by the examination of
gonad tissue smears under a microscope. Oysters which show dominance in
‘maturing stage’ of gonad development are preferred since the conditioning
period will be relatively short when compared to the spent/ indeterminate
stage oysters.

The selected oysters are cleaned thoroughly with wire brush to remove the
plants and animals adhering to the shell. A batch of 25 oysters are placed on
a synthetic twine-knit PVC frame in 100 1, FRP tank (75 x 50 x 25 cm), and
raw seawater pre-cooled at 20-22° C, is filled in the tank. Aeration is provided.
The tanks holding the oyster broodstock are cleaned daily to remove dirt,
faeces and pseudofaeces and filled with fresh raw seawater. After cleaning, the
water level in the tank is maintained at half the height of the tank and 15 litres
of mixed phytoplankton, cultured in outdoor tanks using inorganic fertilisers
as medium are added twice during a day, between 09-00 and 17-00 hrs at 4
hours interval. The average cell concentration of the algae is 1 .0 million cells/
ml. Thus the oysters are conditioned by holding them in the conditioning room
at about 5° C below the ambient water temperature. They attain full maturity
in 10-20 days (Nayar et al, 1987 b). The raw seawater used for broodstock
conditioning contains supplementary food and in a subsequent study Nayar et
al. (1988 c) gave mixed microalgae at the rate of 3 liter / oyster / day.

Palaniswamy and Sathakkathullah (1992) conducted experiments at
Tuticorin to spawn the oyster, C. madrasensis outside the spawning period.
They maintained batches of the oysters in the broodstock conditioning room

Seed Production

101

at the rate ot 15 nos/100 1 tank. Water temperature was maintained at 20 ± 1°
C and salinity 32-33 ppt. Mixed algal diet of Chaetoceros sp., Skeletonema sp.
and Nitzschia sp. of 35 1 (cell concentration 0.75 to 1.0 million cells/ml) was
given daily, after water change. Every fortnight 15 oysters were subjected to
29 ± 1°C temperature shock to induce spawning. During August-September
(secondary peak in spawning) between 73.3 and 79.9 % of oysters spawned.
In the following five months (no spawning or feeble spawning in the natural
bed) 20-60 % of oysters spawned. This study shows that spawning in C.
madrasensis can be induced, to a certain extent, outside the spawning period,
by manipulating temperature and providing suitable food to the oysters.

Palaniswamy and Rajapandian (1997) fed six species of microalgae namely
Tetraselmis gracils, Chaetoceros calcitrans, Chromulina freibergensis,
Isochrysis galbana, Dicrateria icornata and Chlorella salina individually, to
C. madrasensis in a 24 hr study, after the oysters were starved for a day. In all
cases, in the first one hour, filtration was the highest. The authors suggested
that it is better to provide the food to the oysters at intervals rather than giving
it at one time.

Nayar et al. (1988 c) conducted a study by feeding C. madrasensis with
mixed phytoplankters viz, diatoms, comprising Chaetoceros affinis,
Skeletonema costatum, Thalassiosira subtilis and Nitzschia closterium and
phytoflagellates, Isohysis galbana and Pavlova spp. at the rate of 3 1 per oyster
per day. The average cell concentration of the algae was 1 million cells/ml.
After conditioning at 22-24° C for 10-20 days (average 14.5 days) 40.4 % of
the oysters spawned. In oysters fed exclusively with Chlorella salina (1-1.2
million cells/ ml) at the rate of 3 1/oyster/day, spawning resulted in 13.6 % of
oysters and in the oysters fed with boiled com flour at the rate of 400 mg com
flour/ oyster/ day spawning was induced in 17.6 % of the oysters (Nayar et al.,
1988b). This study shows that mixed phytoplankton is the preferred diet for
broodstock conditioning. The algal diets given to the broodstock should
always contain two to three species for better results (Utting and Millican,
1997).

In Thailand it was found that fish or shrimp earthen ponds with their
unusual phytoplankton blooms could provide excellent facilities for conditioning
the oyster broodstock (Nugranad, 1991). Utting and Spencer (1991) described
the broodstock conditioning techniques followed at Conwy, UK. The broodstock
of the Pacific oyster ( Crassostrea gigas ) of 70 mm shell length and flat oyster
( Ostrea edulis) of 65 mm shell diameter are held at 22 ± 2°C in tanks having
water flow not exceeding 25 ml/ minute per adult oyster. Each oyster requires
about 200 million cells of Tetraselmis, 2000 million cells of Thalassiosira or
1000 million cells of Skeletonema per day. A mixture of these species on a
proportional basis gives better results than a single species diet. The authors
recommended a food ration, equivalent to 6% of the initial dry meat weight of
the broodstock in dry weight of algae per day.

102

Oyster Biology and Culture in India

Live algae are preferred when compared to diets of 100 % spray-dried
algae (Utting, 1993). Spray-dried algae have often good potential in broodstock
conditioning since they are convenient to use and provide carbohydrate source
leading to glycogen reserves build up required for the de novo synthesis ol
lipid during gonad maturation (Utting and Millican, 1997).

The best diets are those high in Polyunsaturated Fatty Acids (PUFAs),
eicosapentaenoic acid, 20:5 (n = 3) and decosahexaenoic acid, 22:6 (n = 3),
because many adult bivalves are unable to produce these de novo from shorter
chain pre-cursors (Chu and Greaves, 1991). Millican and Flelm (1994) found
that fecundity, dry meat weight and larval survival of O.edulis were higher
when broodstocks were given diets containing ‘Tahitian’ Isochrysis than when
Dunaliella tertiolecta was given, since the latter is deficient in PUFAs of chain
length greater than 1 8 carbons. Of the two fatty acids considered essential for
bivalve broodstock, 20:5 (n = 3) utilized potentially during embryo development
(to provide energy) while 22:6 (n = 3) is conserved for structural function
(Helm et al, 1991; Marty et al., 1992). The role of dietary protein for
broodstock conditioning needs detailed study since protein supplies as much
of the energy required during embryogenesis as lipid (Utting and Millican,
1997).

Induced Spawning, Fertilisation and Early Development

Fully matured bivalves can be induced to spawn by giving different kinds of
stimuli like raising water temperature, addition of sperm suspension to a
container holding females, mechanical stress, and addition of chemicals such
as Hydrogen peroxide, Ammonium hydroxide, Sodium hydroxide and Tris
buffer. In India, C. madrasensis is induced to spawn by thermal stimulation.
Approximately 25 oysters, conditioned for about 10-20 days at about 5- 10u
C below the ambient temperature are induced to spawn by transferring them
to 1001 Perspex tank containing 50 1 filtered seawater with temperature range
of 2-4° C above the ambient. A silica immersion heater and a Jumo thermometer
are used to raise and monitor the water temperature in the spawning tank.
Aeration is provided in the tank. The sudden change of water temperature
(thermal shock) induces spawning during the first one hour. If spawning is not
achieved, fresh sperms stripped from a sexually ripe male are added to the
broodstock spawning tank and the sperm suspension induces spawning. The
spawning oysters are immediately transferred to separate spawning trays (one
oyster in each 3 litre glass tray) containing filtered seawater at ambient
temperature. On completion of the spawning the oysters are removed from the
trays. If the female is a heavy spawner and the water becomes highly murky,
it is transferred to another tray to complete the spawning. It is essential to
remove the oysters, on completion of spawning in the trays to prevent the
oysters from filtering the gametes. The egg suspension from each spawning

Seed Production

103

tray is filtered through a 100 jam stainless steel or nylobolt sieve into a
container. The sperms obtained from individual trays are mixed and the
pooled sperm suspension is added to each tank containing eggs. This results
in greater heterozygosity of the progeny. The gametes are mixed and mild
aeration is provided.

Most of the eggs are fertilised within 60 minutes of spawning. The
fertilised eggs settle at the bottom and aeration is suspended. The supernatant
water, containing sperms, unfertilised eggs and debris is removed. Fresh
filtered seawater is added and decanting is carried 3-4 times. This is followed
by addition of fresh seawater and mild aeration. The fertilised eggs undergo
first cleavage within 45 minutes.

Larval Rearing

At the end of 4 hrs after fertilisation, as a result of rapid cell divisions, the
morula stage is reached and at the end of 20 hrs the straight-hinge, also called
D-shelled larva or veliger larva stage is reached (Figure 21). The ‘D’ larvae
actively swim and are siphoned from the tank and reared in 1 tonne FRP tank
filled with filtered seawater and aerated. The D-larvae are semi-transparent;
velum protrudes out and creates strong ciliary current which directs minute
particles of food into the stomodaeum. The actively swimming larvae are
separated by siphoning, leaving the sluggish in the tank. This culling process
is continued for the first 2 days. The straight hinge larvae are stocked at a
density of 5 larvae / ml of seawater in 1 tonne tank for further rearing. The

Fig. 21 . D-larvae of oyster produced in the hatchery. Size 65 pm
Courtesy: CMFRI, Cochin, Kerala

104

Oyster Biology and Culture in India

larvae are fed with phytoflagellates, Isochrysis galbana and Pavlova lutheri at
the end of 24 hrs from fertilisation. During larval rearing, the water in the
rearing tanks is changed daily with fresh filtered seawater and then food is
given. Aeration is provided. The sequence of the development of the larvae
from the straight hinge stage to the pediveliger stage is given below.

Stage

Size |jm

Hours / Days

Straight-hinge

60-70

20 hrs

Early umbo

100

3rd day

Mid umbo

150

7th day

Advanced umbo

260 to 270

1 2th to 1 5th day

Eyed larva

280 to 290

1 3th to 1 7th day

Pediveliger

330 to 350

1 4th to 1 8th day

The rearing density of the larvae at various growth stages and the feeding
protocol with flagellates are given below. The nanoplankters measuring up to
10 pm pass through the sandfilter used for seawater filtration. As a result
additional food is available to the larvae.

Stage of larvae

Number of larvae/ml

Algal cell concentration
in nos/larva/day

Straight-hinge

3,000-4,000

Umbo

4,000-5,000

Advanced umbo

5,000-8,000

Eyed stage

8,000-10,000

Pediveliger

10,000-12,000

On the third day the larval shell is slightly oval in shape and the early
umbo stage is reached. They are filtered through 80 pm sieve. On the seventh
day the umbo on the shell is distinct and pronounced concentric rings are seen
on the larval shell. Between 12 and 15 days the late umbo stage is reached
(Figure 22). In 13 to 14 days the eyed stage is reached with the appearance
of characteristic eye spot. The pediveliger larvae start setting within 24 hrs or
sometimes it is prolonged by 2 to 6 days depending on the availability of
favourable substratum. Before metamorphosis, the oyster larvae permanently
cement themselves to a suitable substrate and this is called settlement. During
larval rearing, mortality of 2 to 3 % per day was considered as normal by
Nayar et al. (1984). In a study on the effect of salinity on the growth of D-
larvae of C. madrasensis till settlement at 29.1 to 32.4° C temperature range,
Nayar et al. (1988 c) observed faster growth rate, 20.1 pm/day at 25 and 19.5
pm/day at 30 ppt salinities when compared to 18.0 pm/day at 20 and 16.4 pm/
day at 35 ppt salinities of the water medium.

Utting and Spencer (1991) stated that the D-larvae of C. gigas can be
grown at densities of 15-20/ml but growth and survival have improved

Seed Production

105

Fig. 22. Late Umbo stage of oyster larvae. Size 260 gm
Courtesy: CMFRI, Cochin, Kerala

considerably at densities below 10/ml. They stated that mixed algal diets are
preferred and a suitable diet for the D-shelled larvae is a mixture of Chaetoceros
and Isochrysis’, the most suitable cell densities are 125 cells/ ml and 50 cells/
ml respectively. The number of algal cells/larva/day is higher than that reported
from India. They suggested that with high densities of larvae, it is necessary
to add the total daily ration in two or more feeding sessions. The larval culture
is carried in static water systems (i.e., flow-through system avoided).

Preparation of Cultch Materials and Spat Production

The cultch materials used in the hatchery must be non-toxic and clean. They
should be compact to allow sufficient water circulation in the rearing tank and
hard enough to withstand handling. They should not alter the water quality.
The most common materials used for the setting of oyster spat in the hatchery
are oyster shells, shell grit and polythene sheet; the most preferred are oyster
shells. A hole is drilled at the center of the shell, brushed well, washed in
chlorinated water and pretreated by soaking and repeated washings in seawater.
By this process the pH of the water in rearing tanks will not be affected. These
shells are spread uniformly at the bottom of FRP tanks containing filtered
seawater and several rows of shell rens are also suspended in order to increase
the surface area for settlement in the tank (Figure 23), when majority of the
larvae pass off the eyed stage (300-350 pm). In a 200 x 100 x 50 cm tank 400-
500 oyster shells are laid (P.Muthiah, personal communication and Rao et al.,

106

Oyster Biology and Culture in India

Fig. 23. Shell collectors suspended in the larval rearing tanks in the hatchery for
the collection of oyster spat
Courtesy: CMFRI, Cochin, Kerala

1992).The larvae are released into the tanks at a concentration of 2 larvae/ ml
and the setting tank is well aerated. The larvae are fed with Isochrysis at the
rate of 10,000-12,000 cells/ larva/ day. During the next few days the larvae set
on the shells and majority of the larvae settle on the concave side of the shells.
The spat settlement is 70 to 80/ oyster shell (Rajapandian et al, 1993) and in
a separate study Muthiah (personal communication) gave the average as 39
spat/ oyster shell (Figure 24). The production of attached spat for a 1 tonne
tank holding 400 oyster shells is 15,630 (RMuthiah, personal communication).

Oyster shell grit and polyethylene sheets are used for the production of
cultchless spat. Oyster shell grit of 0.5 mm in size are washed thoroughly,
sterilised in 10 ppm chlorine, washed once more in running filtered seawater
and dried. The shell grit are uniformly spread at the bottom of one tonne
capacity FRP tank and the larvae at setting stage are released. For setting on the
polyethylene sheet the bottom and sides of the tank are lined with pretreated
polyethylene sheet and the released larvae settle on the sheet. In the larval
setting tanks, before feeding, water is completely changed on alternate days
and half the water is changed on the other days. It takes 5-6 days for larval
setting. The spat are reared for three weeks and are fed with mixed phytoplankters
such as Chaetoceros sp, Skeletonema costatum, Thalassiosira subtilis, Nitzschia
spp. etc. Average setting on polyethylene sheet is 4 spat/ cm2 (Nayar et
al, 1987b). In a study on the rate of spat setting, Nayar et al (1988 c) observed
that the D-larvae of C. madrasensis, reared at 29.1 to 32.4° C in the hatchery
gave spat production of 2.6 to 7.9 % of the initial larval stock.

Seed Production

107

Fig. 24. Oyster spat, set on shell collector in the hatchery
Courtesy: CMFRI, Cochin, Kerala

The chemicals epinephrine and nor-epinephrine added at concentrations
of 10'4M - 10 5 M are said to induce oyster larvae to settle and metamorphose
for the production of cultchless spat (Coon et al., 1986).

For spat rearing, nursery upwelling systems are suitable for oysters,
immediately after settlement (Utting and Spencer, 1991). Spat growth is
largely dependent by the quantity of food available for feeding. The ration is
calculated on dry weight of algae. One million Tetraselmis cells are equivalent
to 0.2 mg dry weight. Feeding a ration of 0.4 mg dried algae per milligram
(live weight) of spat per week provides good spat growth (Utting and Spencer,
1991). These authors gave the following dry weights of algae species commonly
used in the hatcheries.

Dry weight (mg) per million cells

Species of algae

Weight

T- ISO

0.02

Skeletonema costatum

0.032

Chaetoceros calcitrans

0.007

Choromonas salina

0.13

3 H ( Tetraselmis pseudonana )

0.02

Tetraselmis suecica

0.20

Culture of Algal Food

The success of hatchery operation largely depends on providing adequate
quantities of suitable micro-algal food to the larvae and spat of the oysters. At

108

Oyster Biology and Culture in India

the Tuticorin Shellfish Hatchery of CMFRI, it has been observed that the ideal
phytoflagellate for feeding the larvae of C. madrasensis is Isochrysis galbana,
a member of the class Haptophycae. Apart from this, species of Pavlova ,
Dicrateria and Chromulina have also been tried as food and satisfactory
results obtained. All these flagellates measure 7-8 pm and have 26-38 % of
protein by body weight (Nayar et al., 1987 b). Once the larvae set and become
spat, they are fed with mixed culture of micro-algae comprising mostly
diatoms and other phytoplankters.

For the isolation of the required species of micro-algae five methods are
in vogue namely, pipette method, centrifuge or washing method, by exploiting
the phototactic movements, by agar planting, and serial dilution culture
technique(see Gopinathan, 1982).

Serial Dilution Technique: In India, the serial dilution technique has been
used for the isolation of the phytoflagellates (Nayar et al, 1987 b ; Gopinathan,
1996). A detailed account of this method was given by Soumia (1971). In this
method, mainly five dilution steps (the inocula corresponding to 1, 10'1, 10 2,
10'3 and 10 4 ml) are employed for the isolation of the required species and
nearly 25 culture tubes (15 ml) are required. After filtering the seawater
through 10-20 pm sieve, the filtrate is inoculated to five series of culture tubes
in various concentrations. This is kept under sufficient light (1000 lux) with
uniform temperature (25° C) conditions. After 15 days some discolouration is
seen in the culture tubes due to the growth of micro-algae. This culture is
further purified by sub-culturing it in 500 ml or one litre conical culture flasks.
Once the culture is completely purified, it is transferred into 3 or 4 litre
Haufkin culture flasks and maintained as stock culture. The stock culture can
be maintained for 1-2 months.

After the isolation of the desired species in culture tubes, they are sub¬
cultured again in a few 50 ml test tubes. These test tubes form the base for the
continuous supply of axenic live algae for the large-scale micro-algae production
system in the hatchery.

Culture Media: For the successful culture of the micro-algae various
chemical culture media are used. Although most algae are photoautotrophic
and can grow in purely inorganic media, others require organic compounds
and the requirements may be either absolute or stimulatory. Usually for
culturing the flagellates the Conwy or Walne’s medium (Walne,1974) is used
at the Tuticorin shellfish hatchery for the maintenance of stock culture as well
as mass culture (Nayar et al., 1987 b).

Growth Phases of the Algae: During the laboratory culture of the micro¬
algae, increase in cell numbers follows a characteristic pattern comprising 5
phases. In the lag or induction phase, there will be no cell division for a few
hours among the cells inoculated to a new flask. The exponential phase is
characterised by rapid cell multiplication and growth which continues till the

Seed Production

109

culture reaches to a maximum level. In the declining phase, the growth and
multiplication of the cells is arrested and slowly the cell numbers decline.
After the arrested growth, the culture passes into the stationary phase, marked
by the absence of further cell division for a few days. Actually this phase is
prolonged in the case of flagellates and they may develop some cover, cyst or
matrix around their body for thriving in the unfavourable conditions. Finally
during the death phase the cells loose vitality and die, rendering the culture
useless.

Stock Culture Maintenance: These are maintained in 3 or 4 litre Haufkin
culture flasks. Autoclaved or boiled seawater, after cooling is provided into
the Haufkin flasks and required nutrients (Walne’s medium) are added. About
10 ml of the inoculum in the growing phase is transferred to the culture flask
and the same is placed in front of two tube lights (1000 lux). The exponential
growth phase usually peaks after 8-10 days and the illumination is reduced to
one tube light. In the stationary phase the culture can be maintained for two
months in the stock culture room under controlled light and temperature, and
with or without aeration. At the peak exponential growth phase the culture
turns dark brown in colour and the cells remain in suspension without
movements.

Mass Culture : The mass cultures are raised indoors by using the fully
grown inoculum from the stock culture in 10 1 polythene bags, 20 1 glass
carbuoys, 100 1 perspex tanks and 250 1 cylindrical transparent FRP tanks.
Nutrient medium is added to these containers. They are held on wooden racks
and provided with light and aeration (Figure 25). The algal cells usually reach
the maximum concentration in 4-5 days and are harvested. In the out door
mass culture of diatoms and nannoplankters, commercial inorganic fertilisers
are used along with the mixed phytoplankters from raw seawater (after
filtering the zooplankters) from the inoculum (Figure 26).

Harvest: The fully-grown algal culture is harvested during the exponential
phase, after determining the cell concentration. During the declining and
stationary phases, the load of metabolites will be very high and the algal cells
may not be in the healthy condition.

General Conditions: For the axenic cultures, the glassware are sterilised.
Most flagellates require low light intensity during the stationary and declining
phases. Twelve hours of light and 12 hours of darkness is maintained in the
stock culture room and indoor mass culture facility. This is achieved by auto¬
time controlled switch. Normal room temperature of 28-30° C is not conducive
for micro-algae culture. The temperature in the culture room is maintained at
23-25° C by air conditioners. It is essential to aerate the micro-algae holding
containers as it promotes growth, keeps the culture in suspension, uniformly
distributes the nutrients in the water column and supplies the carbon dioxide
required for photosynthesis.

Oyster Biology and Culture in India

110

Fig. 25. Axenic culture of microalgae in the shell-fish hatchery at Tuticorin
Courtesy : CMFRI, Cochin, Kerala

Fig. 26. Outdoor culture of microalgae
Courtesy: Surya Hatcheries

TRANSPORTATION OF OYSTER SEED

The farmed oyster grow out areas are not always suitable for the collection

Seed Production

111

of seed in required quantities. In such situations live transport of oyster seed
either from the hatcheries or from the sites where natural seed occur in
abundance, is resorted. The best example is the long distance transport of the
hardened seed of the Pacific oyster C. gigas from Japan to the USA by ship
involving 10 days journey. This began in 1920s and continued till 1970s (with
a break during second world war). This practice helped to build and sustain
the oyster production along the U.S. Pacific coast. This species is not native
to the USA, and apart from several introductions, the import of the seed
resulted in the successful spawning and establishment of the populations of
this species in areas around Hood canal and Wilapa Bay in the Washington
state (Chew, 2001). Hardening involves periodical exposure to air and this is
best done by keeping them in the midtidal zone in the coastal water. Further
details on the hardening of C. gigas seed are given in Chapter 10. Hardening
helps the seed to resist environmental stress resulting in higher survival during
transport.

In India, hatchery raised and hardened C. madrasensis seed were
transported to several places, mainly to assess the suitability of the sites for
developing oyster culture. For hardening, the oyster seed are held in a container
and covered by a wet piece of gunny cloth (soaked in seawater and excess
water drained) for 24 hours. Then they are transferred to a container filled with
filtered seawater and aerated for the next 24 hours. This process is repeated for
about 10 days (Chellam et al, 1988). Experiments conducted on the hardened
and normal C. madrasensis seed showed that the former can be maintained in
semi-arid condition up to 120 hours with 76% survival while in the latter the
survival was 22% (Muthiah,1987).

For transportation, the hardened oyster seed are wrapped in seawater
soaked gunny sheet, and transferred to either box-type cage of 40 x 40 x 10
cm covered with small mesh nylon cloth or tin container (about 161 capacity).
During the transit, once or twice, depending upon the journey time, the seed
are transferred to plastic basins containing fresh seawater lor a few hours and
then repacked as before. The details of the transport ot the hardened seed from
the Tuticorin hatchery to different parts of the country are given in Table 25.
Some adult oysters are also included in the consignments. The longest duration
of the seed transportation was from Tuticorin to Jamnagar involving 36 hr
journey. The mortality rate was low and varied from nil to 9 % except for one
instance when there was total mortality (Table 25) and the reasons aie not

known.

112

Oyster Biology and Culture in India

Table 25. Particulars of C. madrasensis seed transported from Tuticorin to different
places

Year

Sent to

Number

of seed

Size

(mm)

Mode of
transport

Duration of

transport

(hrs)

Mortality

1981-82

Madras

250

15-25

Road

0.4

1981-82

Narakkal

2,500

15-20

Road

Nil

1987-88

Jamnagar

5,800

8-38.5

Road and Air

1988-91

Jamnagar

5,500

9-60

Road and Air

100%

1988-91

Jamnagar

10,000

1-5

Road and Air

Nil

1992-93

Cochin

4,500

10-55

Road

Nil

1992-93

Calicut

4,500

10-55

Road and

Train

Nil

1992-93

Mangalore

4,500

10-55

Road and

Train

Nil

1992-93

Karwar

4,500

10-55

Road

Nil

1992-93

Madras

4,500

10-55

Train

Nil

1992-93

Kakinada

4,500

10-55

Train

Nil

1995-96

Pondicherry

1,500

1.4-42.6

Road

Nil

1995-96

Karwar

3,725

27.3-58.4

Road

Nil

Source : Chellam et al (1988) and Muthiah et al ( 2000)

QUESTIONS

1 . Write on seasonal occurrence of natural spat of oysters at different places
along the Indian coast.

2. Describe briefly the techniques used in induced breeding, larval rearing
and spat production of oysters in the hatchery.

3. Give an account on the culture of micro algae in oyster hatchery.

4. Write short notes on: a) Oyster brood stock selection and conditioning in
hatchery b) Preparation of cultch materials for spat collection c) Serial
dilution technique for isolation of algae d) Transportation of oyster spat.

Chapter 7

Technology of Farming

IN India, Homell (1910 b) initiated oyster culture experiments by laying
lime coated tiles for spat collection in the Pulicat Lake, near Chennai on
the east coast. Awati and Rai (1931) reported that the oysters collected during
March-May were stocked in farm sites at Kelwa, Navapur and Utsali in
Maharashtra. This was basically a holding practice till the oysters were
marketed during October-May. Concerted efforts to develop the oyster farming
technology have been made since 1970 ‘s at the Tuticorin Research Centre of
CMFRI. Initially natural seed were used. The development of hatchery
technology for large-scale oyster seed production in 1982 at the Shellfish
Hatchery of CMFRI, Tuticorin gave further impetus for oyster culture. Several
location testing programs for oyster culture have been taken up at many
centres along the Indian coast, using both the natural and hatchery seed. As
mentioned in Chapter 6, the Ashtamudi Lake in Kerala has proved to be a
good site for natural seed collection and farming the oysters, leading to small-
scale oyster culture by villagers.

SELECTION OF FARM SITE

Several physical, chemical, biological and social factors are to be considered
for selecting the site for oyster farming. Site selection also depends upon the
type of oyster culture.

Water Depth and Type of Substratum

Intertidal and shallow subtidal areas are suitable for on-bottom culture but the
bottom should be firm. For off-bottom culture (racks, stakes, rafts and long
lines), the nature of the substratum is of little concern. For stake and rack
methods of culture 1-3 m depth is suitable; the raft and long line culture
systems are practiced in coastal waters where the depth is 5 m or more.

Tides

Tidal height is of no consequence in the raft and long line cultures. The rack
and stake farms are generally located at subtidal areas, but short duration tidal
exposure of the oyster stock in the intertidal areas renders farm maintenance
easy. The water flow due to the tidal cycle is of little concern in the on-
bottom culture but may cause movement of rens and trays in the suspended
culture.

114

Oyster Biology and Culture in India

Protection from Wave Action

Areas prone to strong wave action are not suitable for oyster culture since they
stir up sediments in shallow waters reducing feeding efficiency and damage
the farm structures (Quayle and Newkirk, 1989). Experience in the raft culture
of mussels in India showed that in the open coastal waters, the rough sea
conditions do not permit year round farming and only a seasonal mussel crop
of 5-6 months duration can be raised. Sheltered sites such as estuaries, bays
and lagoons are preferred.

Water Quality

This includes temperature, salinity, dissolved oxygen, pH, nutrient salts,
turbidity and productivity. All these factors show seasonal variations and a
quantitative evaluation over a period of time will help in selecting the site. The
critical levels of various factors differ from species to species selected for
culture. For example among the Indian oysters, the rock oyster Saccostrea
cucculata thrives well in marine environment whereas Crassostrea madrasensis
and C. gryphoids are euryhaline, mostly inhabiting in backwaters. Temperature
variations recorded in the different areas in the coastal regions are not much
and are generally within the favourable range. High levels of turbidity interfere
with the feeding of oysters, resulting in reduced growth. Based on the data
collected from oyster farms in India the various parameters considered as
suitable for farming the oyster Crassostrea madrasensis are: water temperature
25-3 1°C, salinity 15-35 ppt, dissolved oxygen 3. 0-5.0 ml/1, pH 7.5 to 8.8, gross
productivity 2.0 to 6.7g C/m3/day and net productivity 1.0 to 4.7g C/m3/day.

Pollution

Three types of pollutants are of prime importance in oyster culture (a) pathogenic
bacteria and viruses, (b) toxic algae, and (c) heavy metals and chemicals. The
source of microbial pollutants and heavy metals/ chemicals are the untreated
sewage and industrial wastes respectively. They enter the culture sites due to
run off from the land. Blooms of toxic algae periodically occur in certain
areas, and are reported from India. The oysters accumulate these toxins in
their body and humans consuming them fall sick, sometimes resulting in
death. Hence areas prone to pollution should be avoided.

Predation and Fouling

They are dealt with under Chapter 4 and a preliminary survey of the site helps
to collect information about their presence. However, a site need not necessarily
be rejected on this account since proper management of the farm takes care of
them.

Conflicts with Other Users

Areas used by others such as for navigation and traditional fishing should be
excluded so as to avoid possible conflicts.

Technology of Farming

115

Access

It is advantageous to have easy access throughout the year to the culture site
since men and materials are to be transported to the farm and harvest to be
carried back.

NURSERY REARING OF SPAT

Oyster spat are reared in nurseries by providing protection till they grow to a
size of 25-30 mm. Nursery rearing ensures good survival of the spat and they
are better off to withstand the adverse conditions and predation. There are
several types of nursery systems, either land-based or located in the water
body. In India, nursery rearing is felt necessary for the hatchery reared spat
since it is expensive to maintain them in the hatchery till they reach 25-30 mm
size for grow out culture. For the natural spat the nursery and grow out
cultures are combined in India.

Natural Spat

In the rack and tray method of farming at Tuticorin, C. madrasensis spat are
collected on lime coated tiles laid in box type cages and held on racks. Spat
set on these tiles attain size of 25 mm in 2 months, and are scrapped from the
tiles for further rearing in box type cages (Mahadevan et al, 1980; Nayar,
1987).

In the rack and ren method of culture practiced at Ashtamudi, strings of
oyster shells suspended from racks for spat collection are also used for grow
out culture and no additional protection is provided to the spat in the early
growth phase. Thus both nursery and grow out cultures are combined, more
oyster shells are added to the strings, which are set much nearer to each other.
This practice reduces the water flow and enables heavier spat set.

Hatchery Spat

Throughout the world, the hatcheries prefer to take out the spat at the earliest
since it is expensive to maintain them longer. In the rack and ren method of
culture followed at Tuticorin, the hatchery raised spat are cultured in the
nursery. Each string of 1.5 m long having 6 oyster shells, with spat attached
is taken out from the hatchery tank 15 days after the spat was set. In the
nursery, 3-4 strings are held in a velon screen bag and these bags are suspended
from racks (Figure 27). The velon screen bag is periodically cleaned to
remove silt, foulers and predators. After 30-50 days of nursery rearing the
bags are removed and the strings are transferred to the oyster farm for
suspension from racks (Rao et al, 1992; Rajapandian et al., 1993).

The stake is the support used for rearing the spat, which are usually set on
the oyster shells. In this method the nursery and grow out cultures are carried
from the same stake. Casuarina or eucalyptus stakes of 1-1.5 m length with a
nail on the top end and two or three nails on the sides, close to the top end, are

116

Oyster Biology and Culture in India

Fig. 27. Oyster shell strings with attached spat held in nylon bags for nursery rearing
Courtesy: CMFRI, Cochin, Kerala

driven into the substratum. Each nail holds in place one oyster shell with
hatchery raised spat of about 4 mm length set on it (P.Muthiah, personal
communication). The top portion of the stake, holding the spat set on oyster
shell, is covered with a piece of velon screen to protect the spat against
predation. The velon screen is removed after 2-3 months of nursery rearing
when the oysters attain 25-30 mm length (Rao et al., 1992; Muthiah et al.,
2000).

GROW OUT CULTURE

There are several methods of farming the oysters and the details are given by
Quayle and Newkirk (1989). Broadly they come under two categories namely
bottom (also called on-bottom) culture and off-bottom culture. They are
further divided as follows:

1. Bottom

(a) intertidal

(b) subtidal

2. Rack

(a) tray

(b) string

3. Stake

4. Raft and long line

(a) tray

(b) string

Those listed under 2, 3 and 4 come under off-bottom culture.

Technology of Farming

117

Bottom Culture

This is a very old method and it is low intensive both for capital and labour.
It is practiced in intertidal or subtidal areas. A major requirement for this
method of culture is a firm and stable bottom, with minimum siltation. This
method of culture has been attempted in the Karapad creek and Korampallam
canal by planting cultchless and attached spat, set on oyster shells. The oysters
attained 75 mm average length at the end of one year (Nayar et al., 1988 a).

Intertidal Bottom Culture: It is well known that the oyster populations in
the subtidal areas grow faster than those in the intertidal region since the former
have access to food without interruption. Greater tidal exposure results in
proportionately slower growth (Summer, 1981; Spencer, 1990; Ruwa, 1990).
Strong wave action during the tidal cycle may displace the oysters and may
also cover them under sand or mud. High levels of turbidity created by wave
action may affect the feeding. Predation by star fishes and rays is high on
oysters grown intertidally. To protect the oysters from rays, in the Arcachon
area in France stakes are planted in the oyster beds and in the Humboldt Bay
in the USA the culture site is fenced (Quayle and Newkirk, 1989). An
advantage of intertidal culture is the low fouling intensity. The shell cultch with
attached spat are planted on the ground during low tide. Apart from predation,
mortality results due to siltation and competition for space. The seed attached
on cultch generally grow into clusters. It is necessary to decluster them into
single oysters or small groups of oysters. In temperate waters this is done when
they have grown to 3-5 cm length; declustering results in mortality up to 25%
(Quayle and Newkirk, 1989). Management practice involves cluster separation,
thinning if density is high, and removal of foulers and predators. Hand picking,
raking or forking are the methods used for harvest.

Subtidal Bottom Culture: It is generally practiced in depths up to 5 m.
This is similar to intertidal culture except that predation control is not easy and
fouling is more intense. The main difference lies in harvesting for which dip
nets, tongs and dredges are used. This method of culture is practiced in Long
Island Sound in Eastern USA (Quayle and Newkirk, 1989).

Rack Culture

The rack is a fixed structure and is constructed either in intertidal or subtidal
areas (Figure 28). The advantages of rack culture include a) independent of the
type of substratum b) faster growth compared to bottom culture c) fewer
predator problems and d) low silting mortality (Quayle and Newkirk, 1989).
A variety of culture devices such as oyster shell strings, trays, tyres, different
types of nets, tubing and sticks may be held on or suspended from racks.

There are several types of racks and in India single beam and parallel
beam racks are mostly used. The single beam rack, as the name implies
consists of a single beam (pole) placed horizontally and secured on several
poles, vertically driven into the substratum. This rack is good for suspending

118

Oyster Biology and Culture in India

Fig. 28. Farm structure - Rack

strings or trays. Two single beam racks running parallel and connected by
cross poles is known as parallel beam rack; it is suitable for tray culture.
Casuarina, eucalyptus and bamboo poles depending upon local availability are
used in the country for rack construction.

Rack and Tray Culture

The advantages of tray culture are rapid growth, production of single oysters
with good shape and high quality meats, and control of stock. The disadvantages
include high production cost, fouling and yield limited to single oysters. In
India, large scale studies on the culture of Crassostrea madrasensis were
initiated in 1978 by the rack and tray method in the Karapad creek and later
in the Tuticorin bay (Mahadevan et al., 1980; Nayar and Mahadevan, 1983).
The oyster farm is situated in the Tuticorin bay on the south-east coast of
India (Figure 29). The racks were erected in the bay where the depth varies
from 0.5 to 1.5 m and salinity from 29.4 to 35.3 ppt. Rarely in the monsoon
season, due to heavy rainfall and discharge of fresh water from creeks in the
area the salinity may drop to 15 ppt. The temperature ranges from 25-31° C.
It is high during April-May (peak spawning season) and low during January -
February when it varies between 25-28° C. The tidal range is 0.3 to 1.3 m.

The rack is constructed by driving six poles, each of 2.4 m in length into
the substratum up to 60 cm depth. These poles are fixed in a line, 2 m apart
and another set of six poles are driven parallel to the first row. These two rows
of poles are connected by tying 2.4 m long cross poles. Above these cross
poles, 8 poles of 5.5 and 6.5 m length are placed and tied to form a platform
which is used for keeping oyster trays. Coir and 3 mm diameter synthetic
ropes are used for tying the poles. Each rack covers 25 m2 area and
accommodates 20 rectangular trays. In 0.25 ha area 60 racks each of 25 m2 can
be erected (Nayar, 1987).

Technology of Farming

119

Fig. 29. Rack and tray culture of oysters at T uticorin. Oyster trays are held on racks
Courtesy: CMFRI, Cochin, Kerala

Lime coated curved roofing tiles of 24 x 1 5 cm size are placed at the rate
of 50 tiles/ tray of 100 x 75 x 15 cm size. The tray is made of 5 mm iron rod
and covered with 2-2.5 cm mesh synthetic twine. The tiles are placed with
their convex side facing downwards. The trays with tiles are placed on the rack
and remain submerged during spat collection (Thangavelu and Sundaram,
1983).

Spat, set on lime coated tiles are grown for two months by which time
they reach 25-38 mm size and are scrapped for further rearing on racks. The
detached single spat are reared in 40 x 40 x 1 5 cm box type cages made of 6
mm M.S. round rods and covered by 12 mm mesh synthetic twine. The cages
with cultchless oyster spat (150-200 nos/ cage) are suspended from racks by
4 mm thick and 1.5 m long synthetic ropes. (Nayar, 1987).

After two months rearing, the oyster seed reach 50 mm length in suspended
cages, and are stocked in 90 x 60 x 15 cm trays at the rate of 150-200 oysters/
tray. The frame of the tray is made of 6 mm welded steel and covered by 20
mm mesh synthetic twine. On a rack of 25 m2, 20 trays are accommodated,
holding 3000-4000 oysters. The oysters are reared, beginning from settlement
for one year, when they attain 80-90 mm length (80-100 g shell-on weight
with meat farming 8-10 %). During the rearing period, periodically the cages,
trays and oysters are cleaned of foulers, and predators such as crabs and
gastropods. The poles of the racks are replaced if needed (Nayar, 1987). The
oysters are harvested when the condition factor (see Chapter 3) is high which
occurs before spawning; soon after spawning the oyster meat looses weight,
becomes thin and flabby, and is not tasty. Rajapandian et al. (1993)

120

Oyster Biology and Culture in India

recommended the harvest of oysters when the condition factor values range
between 120-150. The oysters are harvested by collecting them from the
rearing trays in to a dinghy and brought to the shore. By the rack and tray
method the actual production was 27.5 tonnes shell-on / 0.25 ha/year. The
yield of oyster meat from this farm was 2,475 kg at 9 % of shell-on weight
(Nayar et al, 1987a). In this farm 60 racks were accommodated and each rack
covered 25 m2 area, supporting 20 trays containing 4,000 oysters. In an earlier
study Nayar and Mahadevan (1983) estimated the mortality of oysters as 5 %
in the farm by this method. Rao et al (1992) estimated the production of shell-
on oysters at 120 tonnes/ ha/ year by rack and tray culture.

Since the environmental conditions are relatively stable and the farm site
is protected from strong wave action in the Tuticorin bay, it is possible to
culture the oysters for 12 months in a year, harvesting one crop. As the oysters
are marketable from 60-70 mm size onwards it is worthwhile to investigate
whether they can be harvested between 8- 1 0 months culture and its affect on
production. However, the condition factor of the oysters should be considered
in such studies.

Rack and Ren culture: This method became popular in India and was
adopted by the farmers. The CMFRI is maintaining rack and ren oyster farms
for Research and Development for two decades in the Tuticorin bay, and in the
Ashtamudi Lake since 1993. The racks used are the same types described
earlier with slight modifications. The farming of oyster carried out at the
Tuticorin bay and at the Ashtamudi Lake are as follows:

Tuticorin bay

For spat collection oyster shells are strung on G.l.(NO.lO) wire of 1.5 m
length. Each unit is called a ren. During the peak spawning season (April-
May) the rens are laid horizontally on the racks at 100 rens / rack. The number
of oyster spat collected ranged from nil to 27 with an average of 7 nos/ shell
(Muthiah, 1987). After spat settlement, fresh rens are prepared by providing
inter spaces between the shells with attached spat. These rens have 5-6 oyster
shells with inter spaces of 15 cm between adjacent shells and are suspended
from racks. In one year the oysters grow to an average size of 85 mm (Nayar
et al, 1988a).

Rajapandian et al (1993) have generated valuable data on the rack and
ren method of oyster culture by operating a pilot project at Tuticorin. Hatchery
raised seed of C. madrasensis were used and about 70-80 spat were set on each
oyster shell cultch. The average spat set on oyster shell in the hatchery is 39
(R Muthiah, personal communication). In a 1.5 m long nylon rope (5 mm
thick), 6 shells with attached spat collected from the hatchery were strung by
giving spacers and reared in the nursery for 30 days in velon screen bags . The
velon screen bag is removed and strings are suspended from racks in the oyster
farm for grow out culture. The farm area was 0.76 ha with 96 racks. Each

Technology of Farming

121

occupied 80 m2 area and 80 strings were suspended from a single rack. The
growth data and survival from the time of transfer from the hatchery to the
time of harvest (12 months) are given in Table 26.

Table 26. Average growth of oysters in strings by weight and percentage survival in the
rack and ren farm at Tuticorin. Each string has 6 oyster shells

Period of
rearing in
months

Average weight (kg)
of one string with
oyster spat

Average nos.
of spat/ oyster
string

Average weight
of an oyster
in g

Percentage

survival

0.525

74.0

0.980

65.0

7.00

87.8

1.755

61.0

20.16

82.4

2.585

58.4

35.50

78.3

3.350

56.0

50.40

75.6

4.295

53.5

70.10

72.2

4.800

51.0

83.80

68.9

5.250

49.0

96.40

66.2

5.800

47.0

112.20

63.5

6.240

45.0

127.00

60.8

6.920

43.0

148.00

58.1

7.350

39.0

175.00

52.7

Source: Rajapandian et al, 1993.

The oysters have grown from 7.0 to 175.0 g shell-on weight during the
culture period and at harvest the weight varied between 165-181 g/ oyster.
Maximum mortality/ fallout was 12.2 % in the first month (Table 26). The
survival rate at the end of the year was 52.7 %. The production from 3,655
shell rens harvested on four occasions resulted in 27.95 tonnes (Rajapandian
et al., 1 993). This gives a production of 7.63 kg shell-on/ ren and the estimated
production works out to 76.4 tonnes/ hectare/ year. These authors have stated
that the oysters can be harvested at the end of 10 months. Rao et al. (1992)
estimated the production rate as 80 tonnes/ hectare/ year. The oysters are
manually harvested by untying the oyster rens from the racks and individual
oysters are separated from the clusters. After cleaning, the oysters are depurated.

Ashtamudi Lake

Rack and ren method of C. madrasensis culture was initiated in the Ashtamudi
Lake in October 1993.

Farm Site and Hydrography: The Ashtamudi Lake has 32 kin2 water
spread, and has extensive beds of C. madrasensis and S. cucullata. The Lake
supports a wide range of bivalve fauna and the livelihood of more than 3000
villagers is directly or indirectly linked to these resources. The culture site is
located at Dalavapuram, 3 km interior from the Lake mouth. It is well protected
and has good tidal flow from the Arabian sea. The range of tidal amplitude is
0.07 to 1.29 m. The hydrography of the culture site during September 1994 to

122

Oyster Biology and Culture in India

August 1995 (Table 27) indicated that salinity varied from 9 to 15.5 ppt
between July and October and 19 to 31.5 ppt in the remaining months,
dissolved oxygen from 2.0 to 4.6 ml/ 1, water temperature was stable from 28.0
to 30.1°C, pH from 7.66 to 8.8, gross primary productivity 2.0 to 8.9 g C/ m 7
day and net productivity 0.5 to 4.67 g C/ m3/ day (Velayudhan et al., 1998).

Table 27. Hydrographic data of oyster farm at Ashtamudi Lake from September 1994
to August 1995.

Month

Salinity

(ppt)

Oxygen

(ml/I)

Temperature Productivity

Atm water Gross Net

(°C) (°C) (g C/m3 /day)

Sep. 1994

14.0

4.6

31.2

28.0

2.0

0.5

7.9

Oct.

9.0

2.0

29.0

28.0

3.59

2.46

8.0

Nov.

19.0

3.0

29.5

29.8

2.05

1.03

8.8

Dec.

24.0

2.6

29.0

30.1

3.05

1.54

8.74

Jan. 1995

31.5

3.1

30.1

29.9

6.1

4.6

8.10

Feb.

31.4

3.4

30.5

28.8

5.3

4.0

7.79

Mar.

30.1

3.8

31.0

28.0

4.6

3.5

7.85

Apr.

28.0

4.1

31.2

28.2

4.4

3.1

7.77

May.

24.0

3.6

31.3

28.2

8.9

1.3

7.70

Jun.

21.0

3.6

30.0

28.1

5.34

4.01

7.72

Jul.

10.0

4.0

30.0

28.0

6.68

4.67

7.66

15.5

3.4

30.5

28.5

5.30

1.80

7.75

Source : Velayudhan etal., (1998).

Nair et al. (1984) studied the primary production of the Ashtamudi Lake.
At Neendakara, 3 km from the oyster culture site the annual mean net
productivity in the surface and bottom waters was 74.37 and 75.08 mg C/ m3/
hr and the gross productivity 148.09 and 157.60 mg C / m3/ hr respectively.
They stated that the “Ashtamudi estuary is one of the extremely productive
estuaries in the country....”.

During 1993-94, two experiments on the rack and ren method of C.
madrasensis culture were conducted at Dalavapuram by Velayudhan et al.
(1995) and a third experiment was undertaken in the same farm site during
January- August 1995 (Velayudhan et al., 1998), to augment the data base
generated by the earlier study. In experiment A (called ‘A’) 12 oyster rens,
each holding six oyster shells with attached spat (total 471 spat and average
length 28.2 mm) were transported from the Tuticorin hatchery of CMFRI to
the Ashtamudi Lake in October 1993. They were suspended at 2 m depth from
the horizontal platform of a Chinese dip net in the culture site. In experiment
B (called B’) a total of 125 oyster rens, each holding five shells were
suspended in November 1993 from a rack of 30 m2 constructed at a depth of
2-2.5 m, close to the site of the Chinese dip net platform of ‘A’. In December
1993, a total of 15,374 natural oyster spat of average length 24.0 mm were

Technology of Farming

123

found on the rens, and the average number of spat per ren was 123 and per
single cultch 24.6 (Table 28). For experiment C (called ‘C’) the oyster farm
was expanded in December 1994 to cover 0.04 ha comprising 6 racks; the
racks were 2 m apart to provide working space. A total of 825 rens with 4,950
oyster shells were suspended from the horizontal poles of this rack (Figure
30). The cleaned shell rens were treated with 5 % bleaching solution for 10
minutes, after removing the epifauna, to minimize slipping of the spat. In
January 1995, the spat settlement rate was 144 nos/ ren.

Growth: From the initial average length of 28.2, 24.0 and 23.2 mm the
oyster spat have grown to 47.8, 52.0 and 65.9 mm average length in 6 months
in ‘A’, ‘B’ and ‘C’ respectively. The length after 12 months was 63.9 mm in
‘A’ and 68.0 mm in ‘B’ while in ‘C’ the growth was faster and the oysters

Fig. 30. Rack and ren oyster farm at Kerala. Ready to harvest oyster rens are
taken out of the water for display
Courtesy : CMFRI, Cochin, Kerala

124

Oyster Biology and Culture in India

attained an average length of 68.3 mm in 8 months. The average total weight
(shell-on) of the oysters after six months were 13.2, 25.3 and 44.4 g in ‘A’, B’
and ‘C’ respectively. After 12 months the average shell-on weight was 38.3 g
in ‘A’ and 41.0 g in B’ while in ‘C’ the growth was faster and the shell-on
weight was 43.5 g in eight months. The meat weight of the oysters showed a
progressive increase during the first six months of culture but afterwards
registered wide fluctuations. In ‘A’ the highest average meat weight of 4.9 g
was recorded in July after eight months, in ‘B’ it was 5.1 to 5.2 g during
June, September and November 1994 and in ‘C’ the highest average meat
weight was 5.6 g in August, after eight months.

Survival: In ‘A’ the initial density of oysters was 69 nos/ m length of ren
in October 1993 (Table 28). In the following month this number was reduced
to 21 oysters indicating 69.5 % mortality. From November to February there
was continuous natural spat settlement on the rens. As a result, the number
of oysters per metre length of ren reached a maximum of 65 in February.
Natural spat set on the rens was observed for 10 months except in June and
August (Velayudhan et al., 1995). By the end of September 1994 the number
of oysters were reduced to 42 per metre length of ren indicating 64.6 %
survival. In B’ the density came down from 147 to 70 oysters at the end of
12 months culture period with 47.6 % survival. Mortality was high till the end
of April 1994. In ‘C’ from an initial density of 144 nos/ ren in January, there
was a gradual reduction to 72 oysters in June. In July there was fresh spat
settlement and density increased to 125 oysters, followed by a steep decline
to 77 oysters/ m ren in August. The survival was 53.4 % for eight months.
There was considerable recruitment of the spat during the duration of the
culture and the freshly set spat were not excluded in the calculation of the
survival rates.

Production: In ‘A’ the shell-on production per metre of ren was 1 .4 kg
(meat weight 230 g) in May ‘94, for 8 months of culture (Table 28). Thereafter
it narrowly fluctuated to peak 1 .6 kg shell-on weight in September, but the
meat weight declined to 189 g. In ‘B’ the shell-on production per metre ren
progressively increased from 296 g to 2.87 kg for a culture period of 12
months. The meat weight peaked to touch 392 g in June 1994 and there after
it decreased. In ‘C’, the initial shell-on weight of 38 g per meter ren in January
1995 increased to 3.35 kg by August; the meat weight per meter of oyster ren
increased from 2.74 g to 431 g in the same period (Table 28). However, the
total shell-on and meat weights touched peak values of 3.52 kg and 525 g
respectively in July, after seven months culture (Table 28). A total of 550
strings from ‘C’ were harvested on two occasions in August 1995 and a
production of 1.842 tonnes shell-on (meat yield 230.1 kg) was obtained. The
remaining 275 strings were maintained in the farm for further studies.

Technology of Farming

125

Table 28. Production of C. madrasensis per metre ren cultured in the Aashtamudi Lake

Month

Expriment A

Total Shell
no. of on
oysters wt.g

Flesh

wt.

Expriment B

Total Shell

no. of on

oysters wt.g

Flesh

wt.

Expriment C*

Total Shell

no. of on

oysters wt.g

Flesh

wt.

Oct 93

Nov 93

119

Dec 93

227

147

296

Jan 94

324

137

917

160

144

2.74

Feb 94

559

147

106

911

190

137

329

Mar 94

646

156

945

198

127

1,015

141

Apr 94

974

182

1,168

304

120

923

207

May 94

1430

230

1,998

371

2,044

263

Jun 94

1431

220

2,387

392

3,197

301

Jul 94

1377

198

2,454

372

128

3,520

525

Aug 94

1470

176

2,595

352

3,350

431

Sep 94

1608

189

2,610

348

Oct 94

2,850

367

Nov 94

2,870

364

*Study period January-August 1995.
Source: Velayudhan et al. , 1995 and 1998

Based on these studies, Velayudhan et al. (1998) indicated that a 300 m2
rack and ren oyster culture unit, realised a production of 4.25 tonnes shell-on
and 425 kg of meat. They indicated that in one hectare area, 24 racks, each of
300 m2 can be accommodated and production of wet meat and shell per
hectare is estimated at 10.2 and 81.6 tonnes respectively. They have also
worked out the economics of oyster culture (see Chapter 8) and stated that it
can be profitably carried out in the Ashtamudi Lake from November for a
period of 7-8 months. The high intensity of spat fall observed in the Ashtamudi
Lake suggests that it can be developed as a large scale spat collection center
for commercial oyster farming in this area and also to supply seed for oyster
culture at other places.

Rack and Stick Culture: This is a simple method and widely practiced in
Australia and New Zealand (Quayle and Newkirk, 1989). In this system the
oyster seed are collected on narrow sticks and are placed horizontally on racks
for growth. The sticks can be arranged in bundles for seed collection. After the
natural spat set on the sticks reaches under 2 cm length, the stick bundles are
separated and individual sticks are secured on the racks. This method of
culture is not practiced in India.

Stake Culture

In the stake culture the stake is the support for growing oysters while in the
stick culture the stick is the cultch material for oyster spat. The stake culture

126

Oyster Biology and Culture in India

is suitable in shallow waters with muddy bottom. Studies on stake culture of
oysters were conducted at Tuticorin and hatchery raised spat, set on oyster
shell cultch, were used. The details of nursery culture were given earlier.
Nursery and grow out culture are carried on the same stake. Casuarina poles
of 6-7 cm diameter and 1-1.5 m length are driven into the substratum. Each
stake holds 3-4 oyster shells with attached spat. The number of oysters on the
cultch vary from 15-20/ stake. They are harvested at 70 mm length after 10-
12 months (Figure 31). The production is 20-22 tonnes/ hectare with 93 %
survival (Rao et al., 1992; Muthiah et al., 2000). Nayar et al., (1988 a) indicated
that the oysters grown by stake method reach 80-90 mm length in one year and
production of 10-15 t / ha.

Fig. 31. Oyster farm at Tuticorin showing stakes with oysters exposed at low tide
Courtesy : CMFRI, Cochin, Kerala

Rafts and long lines

Rafts and long lines are used in the areas where the depth is 5 m or more. Rafts
are floating structures consisting of wooden frame, supported by floats and are
held in position by anchors laid on the substratum and usually connected by
iron chains to the raft (Figure 32). Locally available wood such as bamboo or
casuarina may be used for raft construction. The poles are placed in a parallel
row and over this another row of poles are placed across. They are tied with
nylon rope to make a rigid frame. In earlier days empty, sealed and painted 200
1 oil barrels were used for flotation but now they are replaced by styrofoam
barrels. The raft may be either rectangular or square in shape. In raft
construction, the expected weight of the harvest should be considered for
providing appropriate floatation. Quayle and Newkirk (1989) stated that a four
barrel raft (each barrel 200 1 capacity) with barrels secured at the corners of
the wooden frame, can support nearly a tonne, less the weight of the wooden

Technology of Farming

127

Fig. 32. Farm structure - Raft

frame. They have stated that the strings of oyster weigh about 5 times less in
water than they do in air.

Like rafts, the long lines also float but can withstand the rough sea
conditions far better than the rafts due to their flexibility. The long line unit
comprises a main line (synthetic rope) of 12 mm or more in diameter,
supported at intervals by floats and anchored at both ends (Figure 33). Oyster
strings are hung from the main line at the rate of 3-4 nos/ m length. Long lines
more than 100 m are often difficult to manage and 50-100 m units are
considered as more suitable (Quayle and Newkirk, 1989). Oil barrels of 200
1 can hold a double long line. On the assumption that a string of full-grown
oysters (7-8 cm) weigh 2.3 kg in water, then 200 1 barrel can support about 50

128

Oyster Biology and Culture in India

Fig. 33. Farm structure showing A. Single long line B. Double long line with floats
and suspended strings.

strings/ m on double long line; barrels may be placed at 8-10 m intervals
(Quayle and Newkirk, 1989).

Rafts and long lines are used for suspended culture of oysters held in trays
or on the strings and sticks; they are similar to those used from racks. The
main advantage of the rafts and long lines lies in the utilisation of greater depth
of water column for oyster production when compared to rack or stake culture
methods. This results in higher production per unit surface area when compared
to other farming systems discussed earlier. In India, while pearl oysters and
mussels have been cultured from rafts and a few experimental studies made on
long line mussel culture, no attempt was made to farm the oysters from these
units. This is mainly due to the rough sea conditions prevailing along the
Indian coasts. Moreover C. madrasensis thrives well in sheltered estuaries and
backwaters.

Location Testing For Oyster Culture

Based on natural and hatchery raised seed of C. madrasensis several studies
have been conducted to assess the suitability of sites at Bheemunipatnam,
Kakinada bay, Pulicat Lake, Muttukadu backwaters, Vellar estuary, Athankarai
estuary, Cochin backwaters, Narakkal, Chettuva, Kunjithai, Dharmadam and
Mulki estuary (Reuben et al., 1983 ; Rao et al., 1994 ; Ramakrishna, 1988 ;
Thangavelu, 1988 ; Sarvesan et al., 1990 ; Patterson and Ayyakkannu, 1997;

Technology of Farming

129

Rao etai, 1983 ; Purushan etal, 1983 ; Joseph and Joseph, 1983) (Figure 34).
These studies have showed that the above mentioned sites are suitable for
oyster farming and a seasonal crop of 6-8 months duration can be raised.

PURIFICATION OF OYSTERS FOR MARKET

During the course of feeding, several pollutants occurring in the aquatic
environment are collected by the oysters and accumulated in their body.
Consumption of these oysters by humans causes several diseases and at times
proves fatal. Bivalves such as mussels, oysters and clams are used as sentinels
to monitor aquatic pollution. The pollutants broadly come under three categories,
namely (a) pathogenic bacteria and viruses, (b) toxins produced by algae and
(c) heavy metals, pesticides and hydrocarbons.

Microbial Pollutants

The discharge of untreated sewage and land drain pollute the oyster growing
areas with bacteria and viruses which in turn are accumulated by the oysters.
The pathogenic bacteria usually found are coliforms ( Escherichia coli ), faecal
streptococci and occasionally pathogens like Salmonella, Shigella, Vibrio
parahaemoliticus and V. cholorae (Gopakumar, 1988). Some of these bacteria
normally occur in the human digestive system, and their concentration increases
due to the consumption of bivalves. Members of the salmonella group cause
typhoid fever while coliforms and vibrios may cause stomach upsets or severe
gastroenteritis.

130

Oyster Biology and Culture in India

The coliform groups, particularly E. coli are used as indicator organisms
because they occur abundantly and generally reflect the possible concentrations
of pathogens from sewage.

Bacteriological and toxicological analyses of oyster meat from the oyster
farm of the Central Marine Fisheries Research Institute (CMFRI) at Tuticorin
showed that E. coli, Staphylococcus and Salmonella were absent (Silas et al.,
1982). Faecal coliform count was very low and within permissible limits in the
oyster Crassostrea madrasensis samples collected from the CMFRI farm and
also from the natural bed at Tuticorin. Also the pathogenic bacteria, Salmonella,
Streptococci and Staphylococci were absent (Pillai and Selvan, 1988). However,
Abraham et al. (1998) reported that the oyster, C. madrasensis collected from
the natural beds of Tuticorin coast were grossly contaminated by human
pathogens such as Salmonella, Vibrio, Staphylococcus aureus, Escherichia
coli, and Enterococcus faecalis.

Most common viral diseases associated with the consumption of bivalves
are caused by pathogens such as Norwalk Like Viruses (NLV), hepatitis A and
enteroviruses (Sindermann, 1990; Enriques et al, 1992; Cliver, 1997). Direct
detection of viral pathogens by using Polymerised Chain Reaction (PCR) will
help to assess the quality of shellfish but the method is complicated and
expensive for routine analysis (Granmo et al., 2001). There appears to be no
information available about the pathogenic viruses from the oysters from
Indian waters.

Toxins from Algae

Of the 5,000 known phytoplankton species (Soumia et al., 1991), some 300
may cause dense blooms and about 40 species produce toxins. Under favourable
conditions such as upwelling of nutrient rich bottom water, some algae multiply
fast and produce blooms and these are generally referred to as “red tides”. The
toxic blooms are mostly associated, with dinoflagellates. The important genera,
as mentioned by Shumway (1990), are Proto gonyaulax, Gymnodinium and
Pyrodinium (vectors of Paralytic Shellfish Poisoning), Dinophysis (vectors of
Diarrhetic Shellfish Poisoning), and Ptychodiscus (vectors of Neurotoxin
Shellfish Poisoning). The diatom Nitzschia pungens is considered to be
responsible for Amnesic Shellfish Poisoning by Smith et al. (1990). Certain
regions in the temperate countries are prone to seasonal outbreaks of shell fish
poisoning and Proto gonyaulax tamarensis which causes PSP is the best
documented among the toxic algae (Shumway, 1990). Mouse bioassay is
commonly used to detect PSP.

From India, three instances of paralytic shellfish poisoning and few
human deaths have been reported from Vayalur village, Tamil Nadu in
1981 (Silas etal., 1982), Kumble estuary, Karnataka state in 1983 (Karunasagar
et al. 1984) and from Vizhinjam, Poovar and Karumkulam, near Trivandrum
in 1997 (Karunasagar et al., 1998). In the first 2 cases the PSP was due to the

Technology of Farming

131

consumption of the clam Meretrix casta and in the third instance due to the
consumption of mussel, Pema indica. It was observed by Karunasagar et al.
(1984) that the clams accumulate the PSP at higher rate and also detoxify at
a faster rate when compared to the oyster, S. cucullata. There seem to be no
reports of DSP, NSP, and ASP toxicity associated with bivalve consumption
from India.

During a two year study in seven estuaries in Karnataka, Karunasagar et
al. (1989) detected PSP toxicity in 5 bivalve species during April 1985 and
March - April 1986. A sample of Crassostrea sp. collected from the Tadri
estuary during April 1985 showed the presence of PSP at a low level of 320/
MU/ 100 g. However, during the last week of March 1986 some shell fish
(species not mentioned) collected from Udyavara / Malpe area showed high
levels, 1 1 00- 1 200 MU/ 1 00 g. Sommer and Myer ( 1 937) reported that sickness
may result in humans at 1000/MU/ 100 g and death at about 2000/MU/ 100 g
level. The DSP toxicity was noticed sporadically at 0.37 to 1.5/MU/g in the
hepatopancreas of bivalves; the DSP symptoms in humans are manifested at
12/MU/g (see Karunasagar et al, 1989).

From Mexico, Mee et al. (1986) reported on the death of 3 persons and
1 8 cases of illness due to PSP toxicity on consumption of oyster Crassostrea
iridescens. Onoue et al., (1980) gave information that 16 persons developed
numbness of mouth due to PSP toxicity in Japan on consumption of C.gigas.
The algal source in the first instance was identified as Gymnodinium catenatum
and in the second as Proto gonyaulax catenella.

Heavy Metals, Pesticides and Hydrocarbons

Lakshmanan (1988) studied the concentration of heavy metals Hg, Cu, Zn,
Cd, Fe, Mn, Pb and Sn in canned and smoked in oil C. madrasensis. The
products, packed in tin and aluminium cans were obtained from Cochin. The
range in the mean values of various metals are Hg 89-101.5 ppb, Cu 46.6-68.6
ppm, Zn 154.6-202 ppm, Fe 69.4-386.5 ppm, Pb nil to 4.6 ppm, Cd 1. 6-3.4
ppm, Mn 4.1-8. 1 ppm, and Sn nil to 50 ppm. Mercury, lead and cadmium were
below the permitted limits of the Indian Standards for heavy metals in canned
fishery products. Copper and zinc were higher in oyster products.

From Cochin area, Sankarnarayanan et al. (1978) have studied the
concentration of copper and zinc in C. madrasensis and from Goa, Zingde et
al. (1976) on the zinc concentration in Crassostrea sp. Sankaranarayanan et
al. (1978) have reported the range of copper and zinc concentration in
C. madrasensis at 70 to 205 pg / g and 2,450 to 12,500 pg / g respectively
while Zingde et al. (1976) obtained 323-2800 pg / g of zinc in Crassostrea sp.
These authors reported higher values for these metals when compared to the
values obtained in the study by Lakshmanan (1988). The results obtained by
Pillai et al. (1986) on the levels of copper and zinc in fresh oysters from
Tuticorin are comparable with those reported by Lakshmanan (1988).

132

Oyster Biology and Culture in India

Mercury poison causes damage to humans through progressive and
irreversible accumulations as a result of ingestion of small amounts repeatedly.
This causes sub-lethal or even lethal effects to the humans (Chichester and
Graham, 1973). Jasmine et al. (1988) studied the mercury content of oysters
C. madras ensis collected from the Tuticorin bay. On dry weight basis, mercury
content varied from 0.0024 to 0. 17 ppm (mean 0.045 ppm). This study showed
that the level of mercury contamination in the oysters was below the limit of
0.5 ppm (FAO 1983).

Although laboratory studies on the accumulation of certain pesticides in
bivalves are available (Mane et al., 1979) it is reported that the pesticides are
not a matter of concern for the quality of oysters in India (Gopakumar, 1988).

The pollutants from the oil products, even in small quantities cause
problems with taste (Nishihama et al., 1998).

Decontamination of Oysters

In several temperate countries, shell fish safety is achieved through monitoring
of the sanitary quality of waters in which it is grown, processing facilities
and shell fish meats before delivery to the consumer (Ray and Rao, 1984).
To make the shellfish safe for human consumption, broadly 3 methods
namely cooking, relaying in clean water and depuration are used (Canzonier,
1988).

Cooking: This is an effective method for oysters which contain labile
microbial contaminants. Fortunately in India the oysters are cooked before
eating. A relatively higher heat processing time is recommended for canning
the bivalves to make them safe from coliforms and faecal streptococci
(Gopakumar, 1988).

Relaying in Clean Waters: The practice of relaying shellfish from polluted
waters to clean waters is widely practiced in the USA and Europe. The oysters
clean themselves from the pollutants. However, this involves additional
expenditure. An effective monitoring program of the oyster culture areas
and the oysters is essential to assess the level of pollutants in the water
and in the shell fish. Monitoring helps to time the harvest either by
preponing the harvest before the toxic effects of the algal blooms are fully
manifested, or closure of the culture sites until the oysters become safe for
consumption.

Recent studies have shown that to some extent depuration of heavy metals
is possible by transplanting the bivalves from contaminated to clean sites and
keeping them there up to three months before harvest (Chan et al., 1999).

Depuration: Depuration is the process where the live oysters are maintained
in filtered seawater, usually in a flow-through system for periods varying from
1-2 days. The oysters clean themselves of the pollutants and also the extraneous
particles such as sand grains by pumping the water. It is essential that care is

Technology of Farming

133

taken to ensure the optimum survival of the oysters during harvest, transport
and depuration process. Weak, injured and animals under stress should be
removed before depuration. The harvested oysters should be brought to the
depuration plant quickly and during transport and storage, the shell fish should
be kept cool and moist. The temperature, dissolved oxygen, salinity and pH of
the water should be maintained at levels optimum for the concerned species.
Filtration of seawater helps to remove suspended particles. It is desirable that
the water is sterilised for use in the depuration plant. It involves (a) Chlorination.
It is the cheapest option, (b) Ozonation. It is an effective sterilising process
and leaves little residue. However, it is a costly process, (c) UV light sterilization.
It is a widely used method of sterilising water for depuration. A great advantage
of this process is the low cost and the absence of residual taints and odours
from chemical residues (Thrower, 1990).

It is recommended that layers of oysters should not exceed 80 mm height
with an overall stocking density of 25 kg per 1000 litres of water. The duration
of depuration depends upon the species, their physiological activity, and
temperature, oxygen and pH levels of the water (Thrower, 1990). The coliforms,
particularly E. coli levels in the oysters are to be assessed to evaluate the
performance of depuration.

Opinions are divided over whether or not depuration removes pathogenic
viruses. Outbreaks of viral infection from depurated shell fish continue to
occur (Thrower, 1990). As the oysters are eaten raw in Europe and America,
strict sanitary control in farming the oysters, as well as elaborate depuration
methods are followed.

At Tuticorin the oysters grown in the CMFRI farm are regularly depurated.
Nayar etal.,( 1983) and Rajapandian etal. (1988) have described the depuration
of farm grown oysters. Harvested oysters are cleaned externally to remove silt
and debris by a strong jet of water. They are placed in trays in one or two layers
(Figure 35). Wooden grids hold the trays above the bottom of the depuration
tank. A drain valve is provided at the bottom of the tank to facilitate flushing
of silt, faeces, pseudofaeces and debris out of the tank. A slow and steady flow
of filtered seawater is maintained in the tank for 12 hours. The oysters are
flushed with a strong jet of filtered sea water and the operation is repeated for
another 12 hours. The oysters are again flushed with a jet of water and are re-
laid in chlorinated (3-ppm) seawater for one hour followed by flushing with
a strong jet of filtered sea water. Ray and Rao (1984) opined that chlorination
is effective at 2-3 ppm levels. Pillai and Selvan (1988) depurated the farm
grown and natural bed oysters and mussels for 24 hours in seawater (water
changed once after 12 hours) followed by chlorination at 3 ppm for 2 hours.
There was significant reduction in the bacterial count. Abraham et cil. (1998)
stated that depuration of grossly contaminated oysters in sand filtered saline
water drawn from a borewell and chlorinated at 5 ppm level, followed by

134

Oyster Biology and Culture in India

Fig. 35. Depuration of oysters. Oysters spread in trays are held in the depuration
tank at Tuticorin

Courtesy : CMFRI, Cochin, Kerala

dechlorination resulted in the reduction of faecal coliforms to the acceptable
level.

In recent years, oyster and mussel culture is fast picking up in the country
and in view of the public health concerns, it is necessary to formulate and
implement measures for monitoring the sediment, quality of the waters in
which the shell fish is grown, processing facilities and shell fish meats prior
to sale. Quality assurance to the public builds up confidence, expands the
market and gives a boost to shell fish aquaculture.

UTILISATION

Raw oysters are widely consumed in Europe and the USA. Details of many
traditional oyster products used in China, the Republic of Korea, Hongkong,
Malaysia and Thailand were given by Chen (1992). In India, a variety of
dishes are made with cooked oyster meat. Nair and Girija (1993) described
several oyster products while Jayachandran et al. (1988) dealt on some value
added products. These include smoked oysters, canned oyster in brine, oil,
masala and tomato, pickles, battered and breaded IQF meat, nectar, chowder,
soups and dried oyster and minced meat products. The shell is used as spat
collector in oyster culture and in the manufacture of Calcium carbide, lime,
fertilisers and cement. The shells, broken to suitable size are used as poultry
feed.

Technology of Farming

135

QUESTIONS

1. Write on various factors to be considered for selecting site for oyster
farming.

2. Describe nursery rearing of oyster spat.

3. What is a rack? Write on rack and ren method of oyster culture.

4. What are rafts and long lines? Describe their advantages over other methods
of culture.

5. Write short notes on: a) Toxins from algae b) Microbial pollutants c)
Depuration d) Stake culture of oysters e) Oyster production by various
methods of culture.

Chapter 8

Economics of Oyster Culture

STUDIES on the economics of any culture operation or any new
technological intervention in the existing farming practices help in decision
making and resource allocation. They also help to improve the management
practices, leading to increased profitability. The assessment of economic
performance of the culture practices includes estimation of annual fixed cost,
annual variable cost, annual cost of production, net income and net operating
income. The annual fixed cost includes depreciation on establishments like
ponds, buildings, water supply systems, major equipment like generators,
FRP tank/ boats etc. The annual variable costs comprise the labour wages,
staff salaries, contingencies such as cost of chemicals, glasswares, input costs
towards seed, nylon ropes, fuel, rafts, stakes, casuarina poles and similar
items. The interest on the working capital is calculated for the duration of the
culture period. The cost of production is the sum of annual fixed and annual
variable costs. The net income is obtained by subtracting the cost of production
from the gross revenue.

The Central Marine Fisheries Research Institute has conducted several
studies on oyster culture along the Indian coast since 1970’s and has set up
Research and Development farms in the Tuticorin bay and Ashtamudi Fake.
These farms are being used for demonstration, training and technology transfer.
Over the years, several aspects of different farming systems have been
experimented and standardised, resulting in fairly consistent production rates.
Based on the experience gained, the economics of oyster culture ( Crassostrea
madrasensis ) by rack and ren method has been worked out. There was no
information on economics of hatchery production of seed and on the stake
method of oyster culture. The information presented here is based on the costs
prevailing at the time of study by the authors. There are no extant laws to lease
the public grounds for oyster farming. As a result the lease rentals are not
included in the economic analysis by the authors.

A preliminary study on the economics of a 0.25 ha oyster farm with 60
racks was conducted by Nayar et al. (1987a). Each rack covered 25 m2 area,
supporting 20 trays with a stock of 4000 oysters. The production from this
farm was 2,475 kg of oyster meat and it formed 9 % of the shell-on weight of
harvested oysters.

Economics of Oyster Culture

137

The rack and tray method is highly suitable for the production of cultch-
free or single oysters of good shape which command high price in many
countries where they are eaten raw, after removing one valve (called half shell
oyster). Quayle and Newkirk (1989) stated that tray culture presents many
problems, usually costlier than other types of culture, should be attempted as
a last resort and may be considered if the purpose is to provide half shell
oysters to the market.

In India, oysters are cooked and meat collected from the shells for
consumption. As a result the shape of the shell is of little consequence. Nayar
et al. (1987a) made several assumptions while working out the economics and
further studies on rack and tray method were discontinued. During the past
two decades, the thrust was on rack and ren method of oyster culture which is
cost effective and was adopted by the fishermen. The information given by
Nayar et al. (1987a) is not dealt here as it has no relevance to the present
situation.

ECONOMICS OF RACK AND REN METHOD OF CULTURE

Two studies, one at Tuticorin and the other at Ashtamudi Lake were conducted
on the economics of oyster culture by this method. Although the economics
of culture operations at these two places as presented below cannot be strictly
compared due to the facts such as the duration of culture, source of seed used
and the realization of the meat from the oysters, these are given to indicate the
economical prospects of this developing culture system.

Rack and Ren Culture at I\iticorin

In the farm at Tuticorin, oyster culture by the rack and ren method was carried
in 0.4 ha area with 50 racks (Table 29). From each rack 100 oyster rens were
suspended from it. Each ren contained 6 oyster shells with attached hatchery
raised spat. The initial weight of the string was 0.5 kg and at the end of one
year, on an average it weighed 7.5 kg. The initial investment was Rs 55,000,
fixed cost Rs 28,215 and the cost of production of 3.25 tonnes of oyster meat
was Rs 82,495. At the end of one year the total revenue was Rs 1,05,000
through sale of 3.25 tonnes of oyster meat for Rs 97,500 and oyster shell for
Rs 7,500. The net profit was Rs 22,505 and the production cost of oyster meat
was Rs 25.4/ kg. The net income was 27.3 % of the total cost of production.
Provision towards the cost of depuration and shucking of the meat was not
made by the authors and if included, the production cost would be higher than
Rs 25.4/ kg.

Rack and Ren Culture at Ashtamudi

The farm covered 300 m2 area and in one hectare area, 24 units of 300 m2 each
can be accommodated (Velayudhan et al., 1998). A total of 1060 rens, each ren
holding 6 oyster shells were suspended from the racks. Natural spat set on

138

Oyster Biology and Culture in India

Table 29. Economic evaluation of C.madrasensis culture by rack and ren method at
Tuticorin [(Rao et al. 1992) modified]

Farm area : 0.4 ha

Production

: 3.25 tonne meat

Duration of crop : 1 year

Items

Investment

Nursery pond

one

20,000

FRP dinghy

one

10,000

Out-board motor 8 H.P.

one

15,000

Pump set 3.5 H.P.

one

5,000

Major farm accessories

5,000

Total

55,000

Fixed cost

Depreciation on ‘A’ @ 33.3 %

18,315

Interest on investment @ 18 % p.a.

9,900

Total

28,215

Operational cost

Oyster seed

6,000

Stakes

50 nos

15,000

Nylon rope

50 kg

5,000

Other farm materials, repair etc

3,000

Labour

10,000

Harvesting charges

7,000

Interest on 1-6 @ 18 % p.a.

8,280

Total

54,280

Total cost of production

82,495

Revenue through sale

3.25 tonne meat @ Rs 30/ kg

97,500

25 tonne oyster shells Rs 300/ tonne 7,500

Total

1,05,000

Total net profit at the end of first year

22,505

Unit cost of production

Rs 25.4/ kg

these rens was used for culture. The duration of the crop was 8 months and
4.25 tonnes shell-on oysters were harvested. The wet meat yield of 425 kg
formed 10 % and the heat shucked meat of 340 kg formed 8 % of the weight
of shell-on oysters. The data given by Velayudhan et al.( 1998) was modified
by a) considering the cost of nylon rope (Rs 1800) and oyster shells (Rs 636)
under operational cost as they are used for one season of 8 months only, b)
interest charges were limited to 8 months for items 1 to 6 under ‘C’ and c)
interest not charged for item 7 under ‘C’ as this activity is carried just before
marketing the oysters (Table 30).

The operational cost worked out to Rs 10,967 and the cost of production
Rs 16,189 (Table 30). The revenue generated was Rs 21,760, net profit Rs
5,571; the production cost of raw oyster meat was Rs 26.1/ kg and heat

Economics of Oyster Culture

139

Table 30. Economic evaluation of C.madrasensis culture by rack and ren method at
Ashtamudi [(Velayudhan et al., 1998) modified]

Farm area: 300 m2 Production : shell-on: 4.25 tonnes

Duration of crop : 8 months

Items Rs

A. Investment

1 . Horizontal poles (6 m) 33 Nos @ Rs 80/ pole 2,640

2. Vertical poles (3 m) 126 Nos @ Rs 40/ pole 5,040

Total 7,680

B. Fixed cost

1 . Depreciation on A at 50 % 3,840

2. Interest @ 1 8 % on A 1 ,382

Total 5,222

C. Operational cost

1 . Nylon rope for rens and racks: 1 5kg @ Rs 1 20/ kg 1 ,800

2. Cost of 6,360 shells @ Rs 0.10 for making 1000

strings including cleaning charges 636

3. Fabrication of oyster rens (1060) @ Rs 0.65 689

4. Labour for erecting the rack 300

5. Harvest charges 750

6. Depuration @ Rs 200/ tonne 1,063

7. Heat shucking, including fuel cost @ Rs 15 /kg 5,100

8. Interest @ 18 % on 1 to 6 for 8 months 629

Total 10,967

D. Cost of production 16,189

E. Revenue

1 . Heat shucked meat @ Rs 60/ kg for 340 kg 20,400

2. Value of shell @ Rs 400/ tonne for 3.4 tonne 1 ,360

Total 21,760

F. Net profit 5,571

G. Unit production cost

1 . Raw meat (425 kg) 26. 1 0/kg

2. Heat shucked meat (340 kg) 47.60/kg

shucked meat Rs 47.6/ kg. The net profit formed 34.4 % of the total cost of
production. For the purpose of comparison with the study at Tuticorin, the unit
cost of production of raw oyster meat (Table 31, G.1) was also calculated by
excluding the heat shucking charges of Rs 5,100. The shucking of raw meat
also involves some labour cost, but the oyster farmer attends to this work. In
the Ashtamudi area, as is the practice at several other places in Kerala, the
oysters are eaten by local people. Velayudhan et al.( 1998) mentioned that in
the local market the cost of 100 shell-on oysters is Rs 25.

A comparison of the net profit on investment in the two studies shows that
in the rack and ren method at Tuticorin it was 32.2 % and at Ashtamudi Lake
34.4 %. Thus the profit margin is comparable between the two studies.

140

Oyster Biology and Culture in India

ECONOMICS OF RACK AND REN METHOD AS PRACTICED BY

FARMERS

Several villagers in Kerala have adopted the rack and ren method of oyster
farming (see Chapter 9) and the profit margin will be much higher since the
cost of labour accrues to the farmer. The actual expense in the farms at
Kayamkulam is given in Table 3 1 . The net profit on investment is 73%. Of the

Table 31. Economics of oyster culture by rack and ren method based on farming as
practised by farmers at Kayamkulam Lake, Kerala

Farm area : 25 sq.m

Number of rens = 500

Production = 2.5 mt (200 kg heat shucked meat)

Duration of culture = 8 months

Investment

Horizontal poles (6m) 15 nos @ Rs.80/ pole

1,200

Vertical poles ( 3m ) 60 nos @ Rs.40 / pole

2,400

Total

3,600

Fixed cost

Depreciation on A at 50%

1,800

Interest @ 18% on A

648

Total

2,448

Operational cost

Nylon rope 5 kg @ Rs.120

600

Cost of 2500 shells @ Rs.0.10

250

Fabrication of oyster rens @ Rs. 0.65

325

Labour for erecting rack ; 2 persons @Rs.150

300

Harvest charges 2 persons @Rs.150

300

Heat shucking charges for 200 kg @ Rs. 15 /kg

3,000

Interest on items 1-4 @ 18% for 8 months

177

Total

4,952

Cost of production

D= B+C

7400

Revenue

Heat shucked meat 200 kg@Rs 60 / kg

12,000

Value of 2 tonnes oyster shell @ Rs 400

800

Total

12, 800

Net profit

F=E-D

5, 400

Unit cost of production

★ ★ -j

Raw meat 250 kg

17.6 /kg

Heat shucked meat 200 kg

37 /kg

*ln operational cost, interest on items C-5 and C-6 were not included as they are in¬
curred at harvest and immediately before marketing

** For calculating the cost of production of raw meat, heat shucking charges of Rs
3000 / under C-6 were excluded

Economics of Oyster Culture

141

production cost of Rs 7,400 the farmers get Rs 1,500 per member and a farm
unit is usually constructed and mangaged by three members who put 500 rens
in 25 sq.m area thereby availing a benefit of Rs 4,500. The financial aid of Rs
4,500 /- is offered by the State government as a grant to the farmers, acts as
an incentive to attract the first generation farmers to venture into oyster
culture. As a result the net profit on investment is very attractive.

As the farmers attend to farm maintanence works such as removal of
foulers, borers and predaters during spare time, the labour cost for maintanence
is not included. Also the farms are located in creeks, close to the residence of
farmers, and there was no labour cost involved for watch and ward.

During the duration of culture (8 months) there was natural spat settlement
on culture rens, thereby adding to the initial stock. At harvest the survival
varied from 45 to 65% of initial stock.

GENERAL CONSIDERATIONS

The casuarina or bamboo poles used in raft construction are to be frequently
replaced due to the damage caused by foulers and borers. Kripa et al.( 2001)
stated that concrete filled 5 cm diameter PVC pipes, used as vertical poles in
the rack construction for mussel culture last for 5 years. The cost effectiveness
of such innovations in farm materials for oyster culture need to be evaluated.

At present, marketing does not appear to be a matter of much concern in
Kerala but needs to be addressed once the production of farm grown oysters
goes up beyond the absorbent capacity of local markets. Also connected with
marketing is the timing of harvest. It has been proved that a seasonal oyster
crop of 6-8 months duration can be raised in the estuaries of Kerala and also
at several other places and that the farm stock should be harvested before the
monsoon intensifies. If delayed, the oysters spawn resulting in poor and less
palatable meat yield. Several oyster products have been developed by the
Cochin based Central Institute of Fisheries Technology and Integrated Fisheries
Project. It is time for the sea food processing industry to take the lead in
utilising the oyster meat in the preparation of diverse and value-added processed
products and expand the market base.

QUESTION

1 . Give economics of oyster farming by rack and ren method.

Chapter 9

Transfer of Technology

RESEARCH and Development, field orientation and trials, and transfer of
technology are the main stages in the development and transformation of
a biological type project to a full fledged self sustaining commercial project
(Lalta and Espeut, 1991). Consequent upon the development of a viable
culture technology for oysters, particularly for C. madrasensis at the Central
Marine Fisheries Research Institute (CMFRI), the Institute initiated need
based awareness and transfer of technology programmes to farmers, State
Fisheries officials and extension workers at different levels with their active
collaboration and participation. The imperative need and importance of this
programme was felt not only to attract the entrepreneurs, but also to diversify
the culture fisheries of the country to other than fish and shrimp culture.
Besides, oyster farming, unlike shrimp culture, does not form a traditional
practice in the country and the entrepreneurs are required to be provided
information on suitable sites, design and culture base, availability of seed,
seeding and rearing the oysters in the system, production potential and
economics of culture. Transfer of technology also envisages training of
personnel, providing adequate knowledge on different aspects of culture
operation and system as a commercial business.

One of the major programmes taken up in this direction, soon after the
development of the technology was under the lab to land programme in 1979.
Eleven families from two coastal villages in Tuticorin, Sahayapuram and
Panimayanagar were selected. All the families belonged to the economically
backward segment of the society, living below the poverty line. After selection
of fishermen families, an orientation training programme was conducted,
wherein various aspects of the techniques of oyster farming were demonstrated
and explained to them. The fishermen erected 33 racks and fabricated more
than 500 oyster rearing cages. Spat for farming was collected from the natural
bed and reared in cages. The fishermen utilized 33% of spare time out of 964
man-days available to them for oyster farming. From the oyster farm, 566 kg
of oyster meat was harvested. This demonstration helped to kindle the interest
in oyster farming in the Tuticorin area to a great extent (CMFRI, 1979)

TRAINING ON OYSTER CULTURE

Following the lab to land programme, the CMFRI conducted regular long

T ransfer of T echnology

143

term (one month duration) and short term training programmes on oyster
farming and hatchery techniques in the Institute. The Trainers Training Center
(TTC) of CMFRI established in 1983 has also organized training on oyster
culture to instructors of extension training centers, teachers, state government
officials, entrepreneurs and farmers in different parts of the maritime states.
Dissemination of results and exchange of information, on edible bivalve
culture including oyster culture were imparted periodically through seminars,
workshops and Summer Schools. To popularize the technology further, a pilot
project on oyster farming was implemented at the Tuticorin Research Centre
of CMFRI in collaboration with the National Agriculture Bank for Rural
Development (NABARD) during 1990-91 and in 1993 a location testing
programme as a prelude to transfer of this technology to other regions of the
coast was organized. Under this programme oyster seed from Tuticorin hatchery
were transported to different Centers viz. Cochin, Calicut, Mangalore, Karwar,
Madras and Kakinada and feasibility tests were conducted. This paved the
way for organizing and implementing a commercial scale oyster culture in
Kerala.

DEVELOPMENT OF OYSTER CULTURE IN KERALA

The programme of development of oyster culture in Kerala was initiated in
1993 with location testing at Dharmadam, Chettuva, Munambam, Narakkal,
Kunjithai, Ashtamudi Lake and Paravur. Of these centers, Munambam was
found to be unsuitable due to heavy fouling ; Kunjithai was only partially
suitable and other centers were found to be suitable to start commercial scale
culture.

The initial demonstration programmes conducted further at selected centers
clearly indicated the significance of three main factors namely, training to
farmers and continuous interaction with the target group; support from local
governing bodies and funding agencies and market development for the farm
produce, for the success of the project. Keeping the requirements of these
inputs in view, the collaboration and participation of the Brackishwater Fish
Farmers Development Agency (BFFDA) and non-governmental organizations
such as Self Help Groups (SHG) formed by women entrepreneurs under the
Peoples Development Programme, were involved in the project. For post¬
harvest and marketing of the cultured oysters, the Integrated Fisheries Project
(IFP) of Government of India is also involved. These combined efforts (as
indicated in the flow chart from Kripa et al., 2004) greatly helped to the
generation of a small scale oyster farming industry in Ashtamudi and
Kayamkulam Lake area. At present annually about 750 to 800 tonnes of
oysters are produced through farming in Kerala. This has also provided
employment opportunities to women in coastal villages.

144

Oyster Biology and Culture in India

SOCIAL IMPACT OF OYSTER CULTURE

Oysters are ideal for aquaculture in developing countries like India. Their
farming requires relatively low capital investment. The grow out or culture
period is 6 to 8 months. In Kerala, oyster farming is a household activity
where all the family members are mobilized to participate in different activities
such as ren making, farm construction, harvesting, postharvest processing and
marketing (Figures 36- 37).

Fig. 36. Oyster farm of women Self Help group at Kayamkulam in Kerala.

Courtesy : CMFRI, Cochin, Kerala

Fig. 37. Harvesting of oysters in Kayamkulam estuary in Kerala
Courtesy : CMFRI, Cochin, Kerala

T ransfer of T echnology

145

Though women were involved in all these activities, their participation is
more in the ren making (punching and stringing empty shells and suspending)
and post harvest processing such as cleaning, shucking and packing. Farm
construction and harvesting is usually done by the male members. Marketing
in some locations (Kayamkulam Lake) was done exclusively by women while
in Ashtamudi Lake the marketing was through Government Department.

A socio-economic survey conducted among the oyster farmers has shown
that some farmers of Kayamkulam Lake utilized the money to meet their daily
requirements. The regular income to the families is through fishing and the
fishers, become unemployed when the trawl ban is implemented during
monsoon. For these fishers the money from the sale of 5 to 10 oyster rens per
day was the main source of income. Some farmers have utilized the money for
meeting the initial expenses connected to schooling of their wards (for purchase
of books, uniforms etc.).

Surveys conducted among the oyster farmers of Ashtamudi Lake and
Kayamkulam Lake showed that the farmers have no complaints regarding the
technology. They have utilized the profit (ranging from Rs 700 to 25,000
depending on the farm size) for various family commitments such as repayment
of existing loan taken for house construction, daughter’s wedding, children’s
education etc. In India, the growth of oyster culture activity is picking up. The
general constraints in the development of oyster culture in India are given in
Table 32.

Table 32. General constraints in the development of oyster farming in India
Constraint Remarks

Lack of awareness about
technology

Marketing of farmed oysters

Ownership of farming
area / legal aspects

Classification of oyster
growing areas according to
pollution index

Availability of finance to
farmers

Exploring external markets
for oysters

Reduction in recurring
expenditure

Infrastructure for depuration

Partly solved by village level participatory
programmes in demonstration farms; wider extension
and need based training are needed.

Partly resolved by collaborating with Government
Agencies; targeted market survey and product
development.

Appropriate leasing policy and inclusion of oyster
farming in State plans needed.

Not resolved. Based on this the oyster trade can be
developed.

Funding by BFFDA available but timely availability of
funds to farmers should be ensured.

Feasibility of single oyster production to be explored;
MPEDA’s and Indian Embassies help needed.

More durable PVC pipes fitted with concrete has
been found to reduce recurring expenditure.

State level action needed.

146

Oyster Biology and Culture in India

The important constraints experienced by the oyster farmers in Kerala
are:

1) Non availability of finance in time for setting up of spat collectors

2) Poaching

3) Damage to farm structures by fishers who try to catch the fish which
aggregate between the rens in the farm.

4) Relatively lower price of oysters, and difficulties in the marketing of
farmed oysters

5) Non availability of area for farming in open estuaries, leasing policy,
and legal aspects.

Nevertheless, the results of oyster farming demonstrations so far organized
and developmental activities initiated in Kerala have greatly helped to motivate
and attract the farmers to this field (Fig. 38). The center-state-farmer
collaborative activies (Fig. 39) has turned out to be a role model for other
maritime states to plan their bivalve mariculture activity.

Fig. 38. Oyster farmer, Mr. Vincent Mukkadan, the first oyster farmer of the State,
also the recipient of best farmer award of Kollam district constituted by the
State Government for the year 1998 speaking on the occasion of Oyster
Farmers Meet organized jointly by BFFDA and CMFRI in March, 2001 .
Courtesy: CMFRI, Cochin, Kerala

OYSTER CULTURE AND RURAL DEVELOPMENT

Rural development in a broad sense is the remunerative activities of rural
residents by using the resources and opportunities available in their communities
and the localities to lead a full creative and healthy life. In the programmes on

T ransfer of T echnology

147

Fig. 39. The center-state collaborative programs in Kerala State
Source: Kripa et al. (2004)

oyster culture in Kerala, participation of villagers was given priority. Their
involvement in farm construction, ren making and harvesting have greatly
induced to develop an urge to own an oyster farm in the villages. Supported
by the financial assistance by BFFDA and marketing by Integrated Fisheries
Project (IFP) and Aquaculture Development Agency in Kerala (ADAK), the
state is poised to double its aquaculture production of oysters in the coming
years. The Rural Development Activity (RDA) of this state is in early stage in
some areas while in Ashtamudi Lake and Kayamkulam Lake it is in an
advanced stage. With the participation of farmers in decision making and
ownership, and the involvement of funding and developmental agencies,
realisation of the production potential, social benefits in terms of employment
and greater income to fish farmers, the prospects and scope of oyster culture
industry in the country is undoubtedly enormous.

QUESTIONS

L Give an account on the technology transfer of oyster culture and the
constraints faced by the farmers.

Chapter 10

Present Status of Oyster Culture in

the World

THE world aquaculture production of molluscs during 2003 was estimated
as 1,22,84,758 tonnes and with a production of 44,96,609 metric tonnes
oysters were the major contributors with 36.6 % . Clams (37,88,158 metric
tonnes) and mussels (15,86,364 mt) contributed 30.8 and 12.9 % repectively.
Scallops, others molluscs, gastropods and cephalopods also were farmed and
the estimates of production during the period 1999-2003 is given in Table 33.
The Pacific oyster, Crassostrea gigas ranked first with an annual production
of 43,76,802 tonnes forming 97.3 % of the oyster produced during 2003
(Table 34). Chew (2001) suggested the possibility that more than one species
are grouped under the Pacific oyster. Next in importance is the American
oyster, C. virginica with a production of 71,711 tonnes (1.5%).

According to Chew (2001) the five major cultivated oyster species in the
order of abundance are C. gigas (China leading production), C. virginica
(predominantly in the east coast of USA), slipper oyster C. iredalei (mainly
from the Philippines), the European flat oyster, Ostrea edulis (European
countries) and the Sydney rock oyster, Saccostrea commercials (Australia).
Other species of importance are C. plicatula, C. rivularis, C. angulata and O.
chilensis. As per the FAO (2003 b) statistics the five top oyster producing
countries by aquaculture (Table 34) are China (82.1%), Japan (5.8 %), Korean
Republic (5.3%), France (2.6 %) and the USA (2.4 %).

CHINA

Molluscs are cultured all along China’s 18,000 km coastline and at least 27
bivalve species are farmed. In recent years the decline in shrimp production
due to diseases has led to intensified efforts in molluscan culture. Zhong-Qing
(1982) dealt with bivalve culture in China while Guo et al. (1999) gave an
overview of molluscan aquaculture in China. Shilu and Linhua (2002) have
rightly called China as a world power for mollusc culture, in spite of the
statement of Guo et al (1999) that “Some Chinese scientists and managers
believe that the official statistics may overestimate the overall production by
20 to 30 %”. The oyster production in China during 2003 was estimated as
3669493 metric tonnes contributing to 82.1% of the global oyster production.
Oyster culture began in China more than 2000 years back. The commonly

Table 33. World mollusc production by farming during 1999-03 in tonnes

Present Status of Oyster Culture in the World

149

T-

■*—

T—

D-

t - N

xt-

cm'

co'

oo'

O’

co'

O’

1 —

T —

O’

T -

i —

O’

co'

oo'

cm'

O’

N-

O’'

to'

T- '

cm'

O’

T-

■<—

T-

'r~

D'-

O’

Is-

T —

cm'

h~'

co'

cd'

T— '

f—

N-

O’

co'

O’

cm'

co'

oo'

O’

1 —

"M"

D-

r—

1 —

O’

O-

D-'

to'

T—

co'

T—

-r-”'

cm'

co'

cm'

co'

cm'

O’

T-

T—

1 —

O’

T-T

oo'

co'

oo'

cd'

co'

1— "

to'

h-'

1—

T—

"r“

O’

1 —

T-

cm'

co'

cm'

oo'

h-'

O’

cd'

cm'

T—

■o

"CD

_CD

150

Oyster Biology and Culture in India

Table 34. World Oyster production and top five oyster producing countries during 1 999-
OS in metric tonnes (FAO, 2003 b). Figures are in metric tonnes

Species

1999

2000

2001

2002

2003

Pacific cupped oyster

36,02,605

39,10,231

41,07,596

42,34,533

43,76,802

American cupped oyster

57,522

42,662

45,058

54,154

71,711

Cupped oysters nei

34,430

17,636

21,172

22,447

21,700

Slipper cupped oyster

14,804

14,222

19,042

12,570

14,500

European flat oyster

6,242

6,039

6,387

7,109

5,226

Sydney cupped oyster

5,024

4,961

4,912

4,605

4,928

Mangrove cupped oyster

1,870

1,632

1,483

1,300

1,313

Chilean flat oyster

291

200

229

235

211

Flat oysters nei

115

187

172

102

Gasar cupped oyster

•

Cortez oyster

685

593

Olympia flat oyster

310

Hooded oyster

Indian backwater oyster

TOTAL

3,722,942

3,998,497

4,207,074

4,337,252

4,496,609

MAJOR OYSTER PRODUCING COUNTRIES

1999

2000

2001

2002

2003

China, Hong Kong SAR

29,88,915

32,92,332

34,91,582

36,26,650

36,69,493

Japan

2,05,345

2,21,252

2,31,495

2,21,376

2,60,644

Korea, Republic of

1,77,259

1,77,079

1,74,117

1,82,229

2,38,326

France

1,39,000

1,35,500

1,09,040

1,15,284

1,17,000

United States of America

87,432

76,953

95,403

93,820

1,08,723

cultivated species are C. plicatula, C. rivularis and C. gigas. Among them C.
plicatula is most important followed by C. rivularis.

Crassostrea plicatula

Zhong-Qing (1982) estimated the production of this species at 83.3 % while
Guo et al. ( 1 999) stated that it forms 50-60 % of the Chinese oyster production.
It is a smaller species compared to the other two and is thin-shelled. It grows
rapidly in the first year, after which shell growth is very poor. Traditionally it
is cultured on stone pilings, vertical strips (over 1 m tall), and bamboo or
wooden stakes. Only natural spat are used for culture and they are available
throughout the year with peaks in May and September. The traditional methods
of culture are the stake method with bamboo stakes and the stone bridge
method. In recent times raft and long line cultures became popular with
farmers since they give higher production and amenable to culture in the open
coastal waters. In some areas stake and stone bridge methods were abandoned
due to low production. Seed collected in May are harvested within a year,
usually from December onwards, touching peak harvest in February, coinciding

Present Status of Oyster Culture in the World

151

with the Chinese New Year. The seed collected in September are harvested
after 14-17 months when they reach the market size of 6-7 cm.

The stake method is suitable for soft bottom. Bamboo or other
wooden stakes of 1.2 m long and 1.5 cm diameter are planted in the middle
tidal flats before the spat fall peaks, at the rate of 1.5-1. 8 x 105 stakes/ ha for
spat collection. The average yield is 60 t / ha but sometimes it may touch 1 10
t / ha.

Zhong-Qing (1982) mentioned about the stone-bridge method used in
sandy mud bottom. Bridges made of stone bars (80 cm x 20 cm x 8 cm
diameter) are used to collect spat on midtidal flats during May/ June. During
7-12 months grow out, the bridges are moved to places to ensure abundant
food supplies. In one hectare 15,000 stone bars are laid and the average yield
is 30 tonnes/ ha. Sometimes the yield may touch 80 tonnes/ ha.

Crassostrea rivularis

This species lives in estuaries of low salinity along most of the Chinese coast.
In Chinese it is called Jinjiang, which means ‘close to river’. Low salinities
are favoured by the spat for settlement. The farmers recognise two forms of
this oyster; the one with white meat is preferred for its flavour and higher
value than the red meat oyster. The culture methods are similar to those used
for C. plicatula. Gravel, oyster shells and cement plates are used for spat
collection. Peak spatfall occurs in June- August when salinity is at its minimum
and temperature at its maximum for the year. Since early 1960’s scientists
have successfully developed spatfall forecast based on larval abundance and
hydrography and help the farmers about the suitable time to lay spat collectors.
The culture site is generally divided into rectangular plots and the spat
collectors are lined up in rows. In a hectare, 3.0 to 3.8 x 104 cement bars of size
40-80 cm x 6 cm x 4 cm diameter or 1.0 to 1.4 x 105 cement plates of 17-24
cm x 14-19 cm size are positioned. After 3-4 years of culture C. rivularis is
harvested. Before harvest, the oysters are removed to fertile grounds for a few
months for fattening (Zhong-Qing, 1982).

In a farm at Guang, concrete stakes, 50 cm long and 6x6 cm at cross
section are used both for spat collection and grow out. A dozen oysters/ stake
is considered as optimum. About 30,000 stakes are planted in a hectare and the
production is 5.448 tonnes of oyster meat (Guo et al., 1999). C. rivularis is
also cultured on shell strings hanging from rafts or long lines. Unlike C.
plicatula, this species grows rapidly for 3 years and harvested after 2-3 years,
at a size of 10-15 cm.

Zhong-Qing (1982) indicated that a raft measuring 84 m2 area gives the
same yield in 2 years which 677 m2 area used for bottom culture gives in 4
years.

152

Oyster Biology and Culture in India

Crassostrea gigas

This species naturally occurs along the Chinese coast and also there were
introductions from Japan. It accounts for 10-20 % of oyster production in
China. The culture depends exclusively on hatchery raised seed (Guo et al.}
1999) and in the hatchery it is carried in 10-100 m3 concrete tanks. Vitamin
supplements and antibiotics are often used. Spat collection in the hatchery is
on strings of scallop or oyster shells. Density of 20-30 spat/ shell is considered
suitable but often spat set is 2-3 times higher. In such cases farmers may break
the spat attached shell into 2 pieces. Each shell costs US $ 0.01-0.02. These
are inserted into nylon ropes and suspended from long lines. At a few places
bottom culture is also practiced.

C. gigas grows rapidly and reaches 8-10 cm in the first growing season.
The seed are produced in hatchery in spring so that the oysters have a full
season to grow. Oysters may be harvested within the first year of grow out.
However, oysters grown in intertidal areas require 2-2.5 years to reach
marketable size.

Triploid oysters are used for cultivation in Shandong and Liaoning
Provinces because of faster growth and higher survival against “summer
mortality”, a syndrome linked to reproduction (Perdue et al., 1981).

In China, raw oysters are rarely consumed. A variety of dishes are made
from cooked oysters and some are dried for storage.

Perspectives: Marine molluscs are among the best loved seafood in
China. The rapid development of mariculture of molluscs resulted in the
deterioration of the culture environment and in many areas the carrying
capacity may have exceeded. The rafts and long lines cover most of the area
of the bays. Red tides became more frequent. Further development depends
upon technological advances towards ecofriendly culture (Guo et al., 1999).

JAPAN

Japan produced 260644 tonnes of oysters in 2003 and occupied second
position by contributing 5.8% of the global oyster production. Aquaculture in
Japan which included oyster culture was dealt by Bardach et al. (1972), Imai
(1977) and Kafuku and Ikenoue (1983) while Korringa (1976a) gave an
account on C. gigas culture in the Hiroshima bay in Japan. In 1670, Kovayashi
of Hiroshima placed bamboo poles with twigs and nets in the seawater,
collected spat and attempted to culture them. This marked the beginning of
oyster culture in Japan (Imai, 1977). The “hanging culture” was developed in
late 1920s and since 1950s oyster culture advanced rapidly by adopting the
raft and long line culture systems.

C. gigas is the most important oyster species farmed in Japan. It is mostly
cultured in two regions : a) along the Pacific coast in the Tohoku region with
the Miyagi Prefecture as its center, and b) the Seto Inland sea with Hiroshima
Prefecture as its centre. C. gigas grows to a maximum size of 35 cm in shell

Present Status of Oyster Culture in the World

153

height and the harvest size is 8 cm onwards. It spawns in summer, and in the
southern Japan it spawns several times while in the north it spawns once in a
year or at times once in 2 years. C. gigas culture is practiced by using the
natural spat.

Seed Collection

Collection of natural spat is limited to a few places such as the Sendai bay of
the Miyagi Prefecture and the Hiroshima coast in the Seto Inland sea. The
former area is most productive for seed collection. The reasons for the high
seed availability in the Sendai bay include large spawning stock of oysters,
temperature rise to optimum level in summer, healthy growth of larvae,
favourable physico-chemical factors contributing towards the retention of the
larvae in the bay, leading to heavy spatfall (Imai, 1977).

In the Miyagi Prefecture area the seed oyster industry is concentrated in
Honshu. As water temperature reaches 20° C in late spring or early summer,
spatfall occurs from May to August with two or more peaks. The August peak
is preferred since fouling intensity is low and survival high when compared to
the spat collected late in spring. The biologists forecast the setting time,
enabling the farmers to suspend the spat collectors. Scallop or oyster shell
strings are suspended from bamboo racks. In Japanese language the shell
strings are called ‘rens’ (Imai, 1977). The ren is folded at the centre and the
two ends are hung from the rack forming a double collector string. A 1.8 m
collecting ren holds 70-80 oyster shells or 100 scallop shells without spacers.
The scallop shell rens are used for cultivation in Japan while oyster shell rens
are meant for export to the USA and Canada where they are better suited for
bottom culture.

In the Inland sea of the Hiroshima coast, spat collection is similar to that
followed at the Miyagi Prefecture except that 2.5 cm spacers made of bamboo,
or plastic are inserted between the shell collectors.

Imai (1977) has given the spat settlement on various shell cultches used
in Japan. The number of C. gigas spat per oyster shell are 20-30, scallop shell
30-60, clam shell 30-50, and abalone shell 30. According to Kafuku and
Ikenoue (1983) on an average, 25 oyster seed are attached to 10 cm height
shell collector. Settlement of 200 spat/ shell is considered as good and about
50-60 survive to the seed oyster size of 1-1.5 cm in about a month’s time
(Bardach et al., 1972). At this stage the rens are removed, the shells are
restrung on thicker wires with bamboo or plastic spacers, 20 cm apart for grow
out culture.

Hardening of Seed

Imai (1977) called hardening of oyster seed as ‘floor-rearing’. The seed are
hardened in intertidal areas, both for domestic and export purposes. The areas
selected for hardening are characterised by weak tidal currents and low food

154

Oyster Biology and Culture in India

availability. Attached C. gigas seed of 5-10 mm size, held on rens are moved
to hardening racks in September. The rens are laid horizontally along the tops
of the racks. The rens are so positioned that the seed are exposed to air for 4-
5 hr during each tidal cycle. The seed hardening is continued through winter
till about February. Hardening results in slower growth, and exposure to sun
and wind thickens the shell margins. They develop resistance to stress. After
hardening they are separated from rens, cleaned of silt, drills etc. and are
packed for export. The hardened seed have better survival and also grow
rapidly when transferred to subtidal grow out facility.

Transport of Hardened Seed

In Japan the technique for hardening the seed of C. gigas was developed
essentially to meet the rigors of 10 days shipment to the USA and Canada.
They are transported in cases, each case holding about 10,000 shells with
attached spat. The cases are covered by straw mats to prevent drying during
transportation. The straw mats are sprayed with seawater two or three times
daily during the voyage to North America. Beginning in 1920 C. gigas seed
were exported to the USA till 1970’s (except for a break during the second
world war). Annually about one billion C. gigas seed (half of Japan’s seed
production) used to be exported to the USA (Bardach et al., 1972).

Bottom Culture

This is the oldest method and the bottom should be firm. Towards this end,
stones, bamboo and empty shells are covered on the substrate. In some places
the culture beds are rectangular 30 to 60 m in length and 4 to 6 m in width,
arranged at intervals of 6 to 10 m. In Ariakekai, C. rivularis is cultured by this
method. The seed are grown for 1 .5 to 2 years with little management practice.
Production is said to be 1.5 kg meat/ m2 (Imai, 1977).

Rack Culture

C. gigas culture is carried in shallow waters of 2-4 m depth at low tide. Rows
of bamboo poles are driven vertically in the substratum and are connected by
horizontal poles. Cross poles are laid on the latter and tied. About 6-10 shells
are strung, 20 cm apart on 1.5 m long string and 20 such strings are hung for
every 3.3 nrarea of the rack. The strings are harvested during the following
spring. Production in the Hiroshima bay is 0.48 kg meat/ m2 raft. Continuous
rack culture in the same grounds in Malsushima bay resulted in decreased
yield and it is attributed to biodeposition of the oysters (Imai, 1977).

Raft Culture

Bamboo or ceder wood poles are used in raft construction. Bulk of oyster
production by farming in Japan is by this method (Kafuku and Ikenoue,1983).
On a raft of 4.5 x 9.0 m about 200 strings are hung. The shells are strung at

Present Status of Oyster Culture in the World

155

10-15 cm interval on rope or galvanised wire of 3 to 6 m length depending on
the water depth, and are hung 40-50 cm apart, from the raft. Spat density of
20/ shell is considered as desirable for optimum growth. Seeded rens are hung
from the rafts in spring following the year of seeding. From October to next
April C. gigas attains about 10 cm size and harvested (Imai, 1977).

The Inland sea of Hiroshima is well protected and sheltered permitting the
use of rafts in waters upto 10 m depth. Here rens with C. gigas seed are
suspended during July-August and by the end of December the individual
oysters weigh 30-60 g. Harvesting begins in December and continues throughout
spring, thus the growing season from spat collection to harvest is 6-8 months.
Between 3-10 % of these oysters are grown for the second year to produce 10-
20 cm oysters specially for half shell market. These oysters are grown in
special book-type hanging cages from rafts. It is stated that the use of hardened
seed gives better growth in oysters cultured for two years. In a typical raft
culture operation in Inland sea, production per ren is 6 kg oyster meat in 6-8
months (Bardach et al., 1972).

In the northern regions of Japan due to colder winter, C. gigas are
harvested after 18 months.

The rafts, in various regions of Japan vary in size from 38.8 to 164 m2.
The number of strings vary from 1.89 to 6.02 / m2 of raft, the number of shell
collectors on rens 284 to 750/ m2 of raft and oyster production 3.5 to 14.83 kg
meat / m2 of raft area (Imai, 1977).

In some regions the spat of C. gigas are collected from the same grow out
sites and in other cases the seed are brought from other areas for planting. In
the same culture site, the growth of oysters on rens suspended from inner rafts
is slower when compared to those held on the racks at the periphery. This is
attributed to lower quantity of food available to the oysters on inner rafts. A
7-month study conducted on the effect of seed density on the growth of raft
cultured C. gigas in Onagawa bay showed that fastest growth of 7.15 g meat
weight was obtained at 10 seed/ shell collector against 4.16 g meat weight
observed at 60 seed/ shell collector (see Imai, 1977).

Long Line Culture

Long line culture is the second major contributor of cultured oysters in Japan.
Introduction of this method enabled to extend the area of oyster culture to 30
m depth. Synthetic ropes and plastic buoys are used (Kafuku and Ikenoue,
1983). This method of culture is practiced at the mouths of bays or in open
coastal waters and is popular in Iwati and Miyagi Prefectures. Compared to
rafts, long lines are advantageous due to lower initial expenses and maintenance
costs, and greater capacity to withstand strong winds, waves and currents. The
seeded rens are hung in spring, and harvesting begins in October of the same
year. The production of C. gigas on long lines is comparable to that of the raft
method of culture. A long line of 60 m length holding 300 rens (each ren 7 m

156

Oyster Biology and Culture in India

long) yields 1.2 tonnes of C. gigas meat in 18 months. In one hectare 44 long
lines of the above size can be located and the estimated production is 53 tonnes
oyster meat. Long lines moored in deeper waters are used for suspending 10-
15 m long rens (Bardach etal., 1972). Growth of C. gigas on long lines located
far away from the shore is not satisfactory (see Imai, 1977).

Comparison of C. gigas Production by Different Methods

A study conducted by Tamura (see Imai, 1977) in the Hiroshima Prefecture on
the production rate of C. gigas by different culture methods showed that raft
culture gives the highest yield of 15.74 kg meat / m2, rack 0.48 kg meat/ m2 and
bamboo pole 0.19 kg meat / m2.

Problems in Oyster Culture

Imai (1977) and Kafuku and Ikenoue (1983) listed the following problems
faced by the oyster industry in Japan.

1 . Oyster culture sites are facing pollution problems due to the discharge
of industrial wastes. 2. Culture sites are concentrated in limited regions and
continuous use of these areas resulted in loss of quality of oysters. Low
dissolved oxygen levels in these sites are attributed to accumulation of organic
matter and insufficient flow of sea water, leading to elevated levels of Hydrogen
peroxide which is toxic to oysters. 3. Fall in water salinity due to heavy rains
causes oyster mortalities. 4. Red tides deplete dissolved oxygen levels and
cause oyster mortalities. 5. Oyster drills such as Thais clavigera, T. beronni
and Ocenebra japanica prey upon oysters and sometimes cause heavy mortality
of the farmed stock. 6. Fouling by barnacles, mussels and bryozoans results in
competition for food and space. Heavy barnacle settlement on the cultch at the
time of oyster spat collection results in low seed production.

Newkirk (1991) stated that the oyster production areas like the Hiroshima
Prefecture may be at their limit of carrying capacity and negative effects of the
high intensity culture and pollution are now limiting the growth.

FRANCE

During 2003 France produced 117,000 tonnes of oysters by aquaculture
comprising 2000 tonnes of flat oyster, Ostrea edulis and 115,000 tonnes of
Crassostrea gigas . Pillay (1990) mentioned that the Portuguese oyster C.
angulata is considered by some to be the same or derived from C. gigas.
Oysters are grown mostly on the bottom since regularly shaped oysters are
produced by this method, to cater to the needs of half shell oyster trade. The
gourmets choice in France is for the half shell of flat oyster, Ostrea edulis. Not
many water bodies are suitable for the culture of this species. The Portuguese
oyster Crassostrea angulata is also cultured traditionally on the bottom.
Natural spat are used for culture. Bardach et al. (1972), Korringa (1976 a,
1976 b) and Pillay (1990) dealt on oyster culture in France.

Present Status of Oyster Culture in the World

157

Ostrea edulis

The most important seed collection area is the north coast of Brittany. The
Gulf of Morbihan is famous for seed collection. Compared to C. angulata, this
species is less hardy and thrives best below low water mark and in higher
salinities (> 25 ppt). Culture period is long due to slower growth and gives low
yield.

Natural spat collection: In the Gulf of Morbihan the season for spat
collection is from June-September when the water temperature is 20° C or
more. Biologists monitor the abundance of oyster larvae in the plankton
collections and provide information on spat setting time to the farmers. They
also monitor the barnacle larval abundance to determine the best time for
oyster spat collection.

Semi-cylindrical ceramic tiles of 13 cm length and 10-12 cm diameter
coated with lime are used for natural spat collection. A stack of three to six
pairs of tiles is tied together for easy handling; the stacks are placed on
wooden platforms, 15-30 cm above the ground. The tiles are left in the
position throughout the summer and fall to receive several successive spatfalls.
Spat set of 30-50/ tile is considered as satisfactory. Natural seed collection is
generally a family operation. Every year some 30 million tile collectors are
laid, producing one billion seed (Bardach et al., 1972). During winter the
thumbnail sized seed are scrapped from tiles for planting on the bottom in
grow out areas, known as ‘parks’ in southern Brittany. The movement of sand
due to the tides may bury the oyster seed and at low tide the sand is manually
removed. The major concern to the oyster seed industry is the low winter
temperatures, resulting in seed mortality.

Bottom Culture in Parks: The parks in the northern Brittany vary in size
from a few to several hectares and are protected from sand and sediment
incursions by the construction of earthen and brush dykes, 30-70 cm high
(Bardach et al, 1972). Sand or fine gravel is spread, after the bottom is
levelled, to maintain its firmness. The shallower areas of the park used for
rearing spat to young oysters are protected by net fencing (Pillay, 1990). The
young oysters are held in the parks for 1-1.5 years, collected and transferred
to deeper beds in 3-10 m of water. Here they are grown for 2 years, collected
by dredging and transplanted back in the intertidal parks for fattening. Planting
the oysters in deeper waters results in better growth and also the culture site
is expanded. The total duration of O. edulis bottom culture is about 4.5 years.
Production rate of O. edulis is 1.7 tonnes/ ha J year (Bardach et al., 1972).

Fattening and Greening in Claires: The word ‘fattening’ is misleading
since the process involves primarily the deposition of glycogen. In France
oysters are fattened after they reach the market size. By this process the oyster
meat increases in size and weight and the colour changes to creamy white with
good flavour. Fattening requires calm, shallow, relatively warm and preferably

158

Oyster Biology and Culture in India

brackish water, rich in plankton. Artificial shallow ponds of 0.1 to 0.2 ha in
size are constructed on marsh land adjacent to sea. These ponds are known as
claires and are connected by a system of gates and channels. The claires are
prepared in summer by draining the water and exposing them to the sun for
several weeks. They are fertilised and filled with water up to 25 cm depth;
water is exchanged twice a month during spring tides. The oysters of about 40
g shell-on weight are stocked in the claires at 4/ m2 in late summer and fall,
and in six months the weight is nearly doubled (Bardach et al., 1972). They
are highly priced and much sought in the French market. The blue-green
diatom Navicula astrearia occurs naturally in some claires and gives green
colour to oyster meat. This so called greening further increases the value of the
flat oyster in the market.

Rack Culture : A common method of O. edulis and C. angulata culture on
the Atlantic coast is the rack method (Pillay, 1990). The natural spat are held
in synthetic bags of 1 m long and 0.5 m wide and these are fastened by rubber
bands to wooden or metal racks, 0.5 m above the ground. Each bag contains
5 kg of 1.5-2 year old O. edulis and a density of 6,000-7,000 bags/ ha is
considered as satisfactory for growth.

Hanging Culture: In recent years this method has become very popular
on the Mediterranean coast of France. Ropes laden with oysters are suspended
in protected areas from metal or wooden frames, ensuring that the oysters are
always submerged. Seed oysters are stuck on synthetic ropes or specially
made wooden poles by using quick setting cement. On a 2 m long rope/ pole
about 75 or 80 oysters are stuck (Pillay, 1990). Foulers are manually removed.
For harvest the ropes are brought to the shore and the oysters are detached.
The yield is high at 5 kg per rope/ pole but the shell is often fragile and tends
to open after harvesting.

Predators and Diseases: The spat are preyed upon by the crabs ( Carcinidas
sp). Major predator of oysters is the starfish Asterias sp. and it is controlled
either by manual removal or by the application of quick lime on the oyster bed.
Large scale mortalities of O. edulis occurred in France from 1968 for a decade.
The protistan parasites Marteilia refringens and Bonamia ostreae were
implicated. The only means of control appears to be to avoid planting oyster
seed during July and August when M. refringens infections occur (Pillay,
1990).

Crassostrea angulata

The seed of this species are also collected on lime coated ceramic tiles which
are placed closer to the shore as they can withstand longer exposure to sun.
The tiles are increasingly replaced by wire mesh bags containing oyster shells.
The shell bags are placed on wooden racks or platforms, 25 to 30 cm above
ground. Generally the seed are left in the collection sites for two years. The
spat collected on oyster shells in bags are grown till harvest with little care.

Present Status of Oyster Culture in the World

159

Sometimes 2 year-old seed oysters are thinned and transferred to new bags.
The oyster seed attached to oyster shells are also sown on the bottom. C.
angulata is basically cultured in intertidal areas within the estuaries (Bardach
et al. , 1972). Those seed grown on soft sediments may be smothered by mud
and are periodically turned and brought to the surface by rakes.

Fattening and greening of C. angulata is becoming popular. This type of
culture takes 4-6 months and the oysters are stocked at 12/ m2 in claires.
Production is 7.5 t / ha/ year (Bardach et al, 1972).

Prospects

The European flat oyster O. edulis is highly esteemed in France and its
cultivation is mainly targeted towards the half shell market. Compared to C.
angulata , this species thrives well at higher salinities, growth is slower and
production rate low. There is growing interest in the culture of C. gigas
particularly after the heavy mortality of C. angulata in 1970’s.

Some farmers use synthetic spat collectors, in place of ceramic tiles. The
close set perforations on the surface allow the lime coating to adhere; the
surface area is enhanced by 25 % over the conventional ceramic tile and the
attached spat are removed with ease by twisting the synthetic collector. There
are machines to punch the shells for ren making, to scrap the oyster seed from
the tiles and to grade the harvested oysters for market. Gathering the oysters
from the ground is also mechanised (Korringa, 1976 a, 1976 b).

A noteworthy feature of the bottom culture of oysters in France is the care
taken by farmers to maintain the park bottom in good condition. Towards this
end, every year up to 1000 m3of crushed stone per hectare is spread on the
ground (Korringa, 1976 b).

PHILIPPINES

In 2003, the production of slipper oyster, Crassostrea iredalei, by aquaculture
was 14,510 tonnes. Bivalve culture in the Philippines was dealt by Young and
Serna (1982) and Joseph (1998) described the mussel and oyster culture in the
tropics which included the Philippines. Bivalve farming began in the Philippines
in early 1900. Oyster farms ranging in size from 100 m2 to 2 ha account for
60 % of the production. C. iredalei is the most favoured species for culture and
is marketed at 6-9 cm in length while to a lesser extent, C. malabonensis, a
smaller species is marketed at 4-5 cm size (Young and Serna, 1982). Several
types of oyster culture are practiced.

Bottom Culture

This is also called as broadcasting method. Spat collectors such as oyster
shells, stones, rocks, boulders, tin cans and a variety of scrap are laid on firm
bottom, as spat collectors where natural setting occurs. In areas devoid of
natural oyster populations, collectors with attached spat are brought and

160

Oyster Biology and Culture in India

scattered on the bed. Subtidal areas are also used for oyster culture. The
oysters are harvested after 8-10 months culture. When grown on stones or
boulders, the oysters are usually harvested at low tide by detatching them,
leaving behind the cultch. This method is not popular, in spite of low investment,
and the disadvantages include: it is substrate specific requiring firm bottom,
production rate low, high oyster mortalities due to siltation and predation, and
harvest is difficult particularly if stones are used as spat collectors (Young and
Serna, 1982; Joseph, 1998).

Stake Method

This method is widely followed and the species grown are C. iredalei, C.
malabonensis and C. cucullata (Angell, 1986). Bamboo stakes of 5-9 cm
diameter are driven into the bottom in rows and are positioned 50 cm apart,
during April-July spawning. The stake is used as the substrate for spat
settlement. Some farmers tie horizontal bamboo pieces to the stakes or attach
empty oyster shells on the stakes to increase the surface area for spat collection.
There are several variations in the stake method. The lattice method of culture
is popular in the Philippines and Ablan (1955) described this method in detail.
The lattices are constructed with bamboo poles of 5-9 cm diameter, held in the
form of inverted ‘V’ and tied together with galvanised wire. Lattice rows are
erected 5 m apart at < 1 m depth at low tide. All the three oyster species
mentioned above are grown by this method (Angell, 1986). This method of
culture is considered as intermediate between stake and rack culture (Angell,
1986). For harvest the bamboo stakes are usually lifted from the water, the
oysters removed on the shore or in a boat, and the stakes discarded. If the
stakes are strong to last for another season, the oysters are scrapped or pulled
off by divers and brought to the shore for separation of clusters. When
compared to bottom culture, stake method has the advantage of low oyster
mortality, faster growth and higher production rate. The disadvantages are
many such as; predators such as crabs and starfish can crawl on the stakes and
attack the oysters; harvesting the oysters from the stakes is difficult; and
bamboo collects fewer spat per unit area than do oyster shell (Young and
Serna, 1982). A 0.5 ha stake culture farm can hold 35,500 stakes producing
about 8,600 1 of shucked oyster meat (Blanco, 1956).

Hanging Method

In this method empty oyster or coconut shells are used as collectors. They are
hung on synthetic twine or heavy monofilament nylon line and are held 10 cm
apart by bamboo spacers; otherwise knots are made in the twine. In some
places, for spat collection, the shells are strung without spacers and then
restrung with spacers for grow out culture. There are several methods of
hanging culture, (a) Strings of oyster or coconut shells spaced about 25 cm
apart on polyethylene rope are hung from a bamboo platform, (b) The cultch

Present Status of Oyster Culture in the World

161

consists of a long line of threaded oyster shells held apart by 10-12 cm long
tubes. Four parallel lines, approximately 20 m long and 20 cm apart are strung
between two bamboo posts. This is a fixed long line directly holding the
cultch. Oysters grow fast by this long line method as they are not crowded,
(c) Oyster shells are held in bamboo tray (1.5 x 1.0 m) with 15 cm sides. These
trays are kept on horizontal supports fixed in near still waters. The oyster seed
are left to grow to market size in the tray. For harvest the oyster trays are
brought to the shore where the oysters are separated. The duration of the
culture is 6-8 months. The advantages of the hanging method over other
methods are: faster growth, higher production, lower mortality from silt and
predators, independent of the nature of substratum, and harvesting is easy.
High cost of the materials is the disadvantage (Young and Serna, 1982).

For market, most of the oysters are transported in the shell. For long
distance markets shucked meat, packed in polyethylene bags, is transported.
Oysters are rarely processed into various products. As per a study conducted
on the economics of various methods of oyster culture in the Philippines by
Librero et al. (1976) the earnings on sales per hectare by bottom culture are
10 %, stake method 36 %, lattice method 50 % and hanging culture 73 %.

Problems

The Becoor bay near Manila, where the first oyster farms were established,
became the leading centre for oyster and mussel production between 1935 and
1950, followed by a decline after 1960, due to microbial and industrial
pollution (Young and Serna, 1982). The growth and decline of shellfish
farming in the Becoor bay is now part of history. Newkirk (1991) stated that
the problems affecting oyster culture in the Philippines are deforestation
resulting in increased runoff and siltation, pesticide and sewage pollution, loss
of mangroves and occurrence of red tides.

THAILAND

The production of oysters by aquaculture in Thailand during 2003 was 16 000
tonnes. Saraya (1982) described bivalve culture; Joseph (1989,1998) dealt
with oyster and mussel culture and Pripanapong and Youngvanichset (2000)
wrote on oyster culture in Thailand. Oyster culture was first attempted in
Chantaburi Province in 1942 and spread to other areas. Its development during
the period 1 942- 1 980 was slow for want of investment incentives. In Thailand,
oysters rank first among the farmed molluscs and three oyster species namely
Crassostrea belcheri (some consider it as C. lugubris), C. iredalei and
Saccostrea cucullata are cultured. In 1995 the total area under culture was
1419 ha and C. belcheri was farmed in 51 % of the area (Pripanapong and
Youngvanichset, 2000). Oyster culture practices include the traditional method
of placing rocks on hard or sand-mud bottoms to semi-traditional method of
installing bamboo or other stakes on the sea bed. Tray hanging culture is a

162

Oyster Biology and Culture in India

recent development but not popular due to high cost of investment
(Tiensongrasmee, 2000). The most commonly used oyster culture methods are
on cement pipe, bamboo stick, cement pole, besides tray culture, and hanging
culture (Pripanapong and Youngvanichset, 2000). Average annual production
rate of oysters in Thailand was estimated by Young and Serna (1982) at 19 t /
ha/ year (culture method not specified).

Bottom Culture

This is a traditional method and large stones or rocks are placed on hard sandy
or sandy-mud bottom. Rocks are piled up in group of 5- 1 0 and these are placed
in rows, 10 cm apart. The spat set on these materials are harvested after 1-1.5
years.

Cement Pipe Culture

Cement pipe of 40-50 cm in diameter is cut into 20-45 cm in length, and
inserted on to bamboo pole which stacks on the bottom. Each set of pipes is
65 cm apart in column and 1.5- 1.6 m in row. Both spat collection and grow out
are carried on the cement pipe. This method is commonly practiced in Surat
Thani and after 18 months the oysters are harvested. The pipes are kept in the
sea bed for about 8 months and C. lugubris attains > 7 cm shell height
(Bromanonda, 1978). This species attains 11 cm shell height in one year.
Average production rate of C. lugubris is 45 oysters per pipe or 75,000
oysters/ 0.16 ha (Bromanonda, 1978). The production of oysters at Surat
Thani area was estimated at 39,400 numbers/ ha / year by Joseph (1989).

Bamboo Stick Culture

Dried bamboo sticks of 1-1.5 m in length are stacked 40-50 cm above the
bottom, 15-20 cm apart from each other in a row. The rows are set 2-3 m apart.
The bamboo stick is used both for spat collection and grow out culture. In
Surat Thani, this method of oyster culture is practiced. High mortality may
occur due to collapse of the bamboo sticks.

Cement Pole Culture

Cement pole of 12-15 cm in diameter and 30-35 cm in length with a hole on
side is inserted on the bamboo or wooden pole. These cement poles are spaced
on the bamboo at 20 cm apart in a row and the distance between the rows is
2. 5-3.0 m.

Tray Culture

Commonly used trays made of hard wood measure 80 x 1 00 x 1 5 cm in length,
width and height. They are suspended from a raft. These trays are also used
by farmers for holding the harvested oysters before they are marketed. Now
used motor cycle tyres as trays became popular among the farmers. The tyre

Present Status of Oyster Culture in the World

163

is divided into two rings with nylon net and lined with rope. Sets of tyres are
hung 1 m apart under a raft. The grow out culture is 6-8 months. Used motor
cycle tyres have >10 years life for tray culture, are cost effective and yield
oysters of good shape for market. Tyres are widely used as trays in the west
coast.

Hanging Culture

Oy ster spat numbering two, taken from a collector are attached together, with
cement on the rope. The ropes are suspended either from racks or rafts.

Hanging culture of ropes with spat cemented, from raft or long line is
most suitable for the west coast, while cement pole and tyre-tray hanging from
raft is found to be well-suited for the east coast.

Remarks

It is of interest to know that apart from split bamboo poles, specially made
cement tubes are used for spat collection in Thailand (Joseph, 1989). The
natural seed set on spat collectors are carefully removed and refixed on nylon
ropes and cement blocks in a linear fashion. Although labour intensive, this
practice helps to seed the grow out substrate at appropriate density to optimise
production. It assumes significance because it is common knowledge that in
some sites the spat fall may be scarce while in others it may be intense and in
such situations the above practice has the potential to play a decisive role in
better utilization of the seed resources. The utilization of the used motor cycle
tyres as substitute for costly, specially made trays is yet another innovation in
the oyster culture practiced in Thailand.

Large oysters, especially C. belcheri are popular and valued high in the
domestic market. Oysters are mostly sold in the domestic market either fresh
or preserved.

The major constraints for the expansion of oyster culture in Thailand are
inadequate seed supply, shortage of suitable culture areas and lack of quality
control (Newkirk, 1991). Tookwinas et al. (1990) described the problems for
oyster culture in Bang Prong Bay in Chonburi Province of Thailand where
oysters suffered mass mortalities during 1989. The mortalities are attributed to
deterioration in the water quality due to high stocking densities and also the
oyster farms covered 80 % of the bay.

QUESTIONS

1 . Describe oyster culture in China or Japan.

2. Write on the importance of oysters in the world aquaculture.

Chapter 11

Recent Developments in
Oyster Culture

DURING the past two decades several developments have taken place in
oyster culture, specially in the hatchery production of seed. In the
nutrition front, systems have been developed to produce live microalgae at
high densities by adding appropriate dose of carbon dioxide in the culture
media, dried heterotrophically grown replacement diets in lieu of live microalgae
and microencapsulated diets as supplement to the normal diet. Success has
been achieved in the cryopreservation of sperms and D- larvae, remote setting
of larvae and use of chemicals to enhance spat settlement. For rearing the
oyster spat, flowthrough systems in the hatcheries and several types of forced
upwelling practices for the nursery rearing of the spat are in vogue. Use of the
concept probiotics is an emerging science in the larval rearing to improve the
health of the larvae. Oyster genetics including selection, hybridization,
polyploidy and biotechnology are the frontier areas of science where significant
contributions have come towards increasing the productivity in the grow
out systems. The use of oysters along with seaweeds as biofilters in purifying
the shrimp farm effluents has received considerable attention. Narasimham
(1998) gave some of the developments in the hatchery production of bivalve
seed.

Broodstock Development and Spawning Induction

Broodstock development in the hatcheries involves considerable expenditure.
It is of interest to note that encouraging results have been obtained by
conditioning the oyster broodstock in waters of high phytoplankton production
such as shrimp farms. Spent Crassostrea iredalei introduced into shrimp farm
showed rapid gonad development and 60 % of the oysters became fully ripe
within 30 days (Wong, 1994). In Thailand, Nugranad (1991) observed that
fish or shrimp earthern ponds, characterised by the presence of phytoplankton
blooms do provide excellent facilities for conditioning the oyster broodstock.

The techniques of conditioning of bivalve broodstocks in the hatchery
were reviewed by Utting and Millican (1997). The authors stated that “ the
objectives of bivalve broodstock conditioning are to maximize fecundity of
parent animals, while maintaining egg quality and larval viability”. Gonad
maturation depends upon food availability, diet quality and water temperature

Recent Developments in Oyster Culture

165

during conditioning. Based on the review they made the following observations.
Live microalgae as food give better results than 100 % spray-dried algae. It is
desirable to use two or three algal species rather than a single species. The best
diets are those high in PUFAs. A suitable ration for bivalve broodstocks is 6
% of the dry meat weight in dry weight of algae per day for most species
reared at 20-22 °C. At lower temperatures 3 % may be sufficient. The role of
dietary protein during broodstock conditioning needs detailed studies. In spite
of several decades of hatchery production of bivalve seed the techniques
available for broodstock conditioning are still far from ideal (Utting and
Millican ,1997).

Apart from thermal shock, the most commonly used stimulant for spawning
induction is the addition of gametes stripped from another oyster. Some
commercial hatcheries remove the ripe gonad portion from the male and
female oysters and place it in a blender with 1 mm filtered seawater. The tissue
is blended for 5-10 seconds. The liquid tissue is passed through 73 pm screen
with eggs collected on a 44 pm screen. Then the eggs are washed in filtered
seawater. Eggs obtained by stripping usually produce fewer larvae than a
natural spawn since immature eggs are included. This method is commonly
used in C.gigas hatcheries (Castagna et al, 1996).

Serotonin induces spawning particularly in males. Serotonin concentration
of 2.0 mM is obtained by dissolving 7.7 mg in 10 ml of 1 mm filtered seawater.
Approximately 0.4 ml of the 2.0 mM solution is injected into the adductor
muscle of the oyster. In about 15 minutes after the injection, ripe oysters
spawn (Gibbons and Castagna, 1984).

High Density Microalgae Production by Adding Carbon Dioxide in
Culture Media

The batch culture practice of raising live microalgae for use as food to the
oyster larvae under axenic conditions usually gives a density of 1.0 - 1.5
million cells/ml. Addition of carbon dioxide gas enhances the microalgae
growth. Carbon dioxide is supplied from compressed gas cylinders, and very
little is needed (about 0.5%) in the air supplied to the algal culture. The carbon
dioxide is passed through a flowmeter, taking care that the quantity used will
keep the pH of the culture between 7.8 and 8.0. The pH is monitored though
a pH meter. Both the air and the carbon dioxide are filtered through an in-line
filter unit of 0.3-0.5 pm before they enter the microalgae culture media (Laing,
1991). By releasing the carbon dioxide gas into the culture media, algae cell
concentrations go upto 6.0 million cells/ml (Wong, 1994).

In the commercial hatcheries in the USA carbon dioxide gas is passed into
aerated algae culture containers for 15 seconds, about every 30 minutes at psi
above ambient pressure to maintain the pH in 7.5 to 8.0 range. This is done in
the hatcheries with a system of electric timer and solenoid valve connected to

166

Oyster Biology and Culture in India

a CO, tank and by manually plurging for a few minutes twice a day (Castagna
et al., 1996).

Preserved and Dried Algae as Replacement Diets

Live microalgae are the natural food for bivalves and considerable work has
been done to utilize dried and preserved algae as a partial substitute to live
microalgae. Centrifugation of algae into a paste form and stored in refrigerator
greatly facilitates its use in the hatcheries. The shelf-life of Thalassiosira
pseudonana concentrate (paste) is more than one year and it is possible to
utilize excess and offseason algal production in paste form (Donaldson, 1991).

In recent years large scale outdoor pond production of a few algae such
as Spirulina and Dunaliella salina has resulted in the bulk availability of
spray-dried powder of these algae in the market. Spray dried extract of
D. salina improved the growth of rock oyster larvae when it was supplemented
with live algae (Numaguchi and Nell, 1991).

Techniques have been developed for the large scale production of marine
microalgae under heterotrophic growth conditions, i.e. utilizing organic carbon
instead of light as a source of energy. The growth of bivalve larvae and
juveniles fed with dried Tetraselmis suecica is comparable to that obtained for
live, light grown (photoautotrophic) T. suecica. The performance of dried
algae was generally inferior to that of controls fed on live algae. Heterotrophic
mass production of algae has been realised for very few species and most of
the species that are known to be of high nutritional value for bivalves such as
Chaetoceros, Isochrysis, Skeletonema, Thalassiosira and Monochrysis are not
capable of growing in the dark (Gladue, 1991).

Artificial Diets

The production of live microalgae as food for bivalves in the hatchery accounts
for about 30 % cost of the total seed production (Coutteau and Sorgeloos,
1993). In this context several attempts have been made to develop suitable
non-algal artificial diets not only to reduce the cost of seed production but also
to find out alternate artificial diet for larval rearing. Langdon and Newell
(1996) have dealt on artificial diets for oysters. The studies by Dunathan et al.,
(1969) and Turgeon and Haven (1978) showed that it is possible to increase
the tissue weight and glycogen content of C.virginica by adding carbohydrate
supplements. Urban and Langdon (1984) conducted growth studies on
C.virginica by providing algae supplemented with various non-algal foods.
They observed that upto 50 % of an algal ration could be substituted with a
mixture of yeast, rice, starch and kaolin without a significant reduction in
oyster growth. These powder diets are nutritionally incomplete, caused water
quality problems and subsequently promoted bacterial proliferation in culture
systems (Coutteau and Sorgeloos, 1993).

Recent Developments in Oyster Culture

167

Microencapsulated Diets

Some progress was made in the development of microencapsulated diets.
Laing (1987) used cross-linked, protein- walled commercially prepared capsules
known as ‘Frippak’ as diet in growth experiments with juvenile C.gigas. He
reported that upto 60 % of an algal ration could be substituted with the
encapsulated diet without significant reduction in growth when compared
with the growth of oysters fed on a full algal ration.

Lipid walled encapsulated diets were also tried on oysters. Langdon
(1982) reported improved growth of juvenile C.virginica fed on algae with
supplements of lipid-walled capsules containing water soluble vitamins
compared with that of oysters fed algae alone. Chu et al. (1987) also used
lipid- walled capsules containing protein, dextrose and vitamin B to C.virginica
larvae. They stated that in some experiments, capsule-fed larvae grew to
settlement and metamorphosis, while no larval settlement was observed in
other experiments (also capsule fed). These authors speculated that the observed
variation in the performance of capsule-fed larvae was due to differences in
the bacterial population present in larval cultures.

Langdon and Bolton (1984) noted that the growth of C.virginica larvae
fed on a microencapsulated artificial diet was reduced by 50 % when antibiotics
were added to the culture medium. They suggested that bacteria are important
in the nutrition of oysters fed on microencapsulated diets.

Feeding microcapsules high in (n-3) HUFA as a supplement to live algae
can improve the growth of oyster seed fed with algae that are deficient in these
essential fatty acids (Langdon and Waldock, 1981). In India, Kandasamy and
Muthiah (1988) used microencapsulated diets as a supplement to live Isochrysis
galbana to the D-larvae of Crassostrea madrasensis. Mean diameter of the
capsule was 3 mm and contained oyster oil or clam oil or fish oil extracts. The
larvae are given the feed at 10,000 or 20,000 capsules as supplement to
l. galbana per day. Spat setting was higher in the larvae fed with oyster oil
extract than the control where I. galbana diet alone was given. Better linear
growth and greater weight increase was observed among the oyster spat fed
with oyster oil and fish oil extracts in capsules, compared to the control where
I. galbana diet alone was given.

The main problems in the use of microencapsulate diets are associated
with selection of suitable capsule type, setting, clumping and bacterial
degradation of the particles, leaching of nutrients and low digestibility of the
capsule wall (Chu etal., 1987; Langdon, 1989). The use of microencapsulated
diets for bivalves at present mostly remain in the research laboratories due to
high cost and difficulty in producing capsules of small size on a large scale
(Coutteau and Sorgeloos, 1993).

Yeast

Studies have been conducted on the use of yeast cells as food for bivalves due
to their high protein content, small particle size and good stability in the water

168

Oyster Biology and Culture in India

column. Further they can be mass produced at low cost. However, poor total
nutritional value of yeast deter it to be used as an exclusive diet in the hatchery.
Urban and Langdon (1984) obtained greatly improved growth in C.virginica
by supplementing 50 % with the dried yeast Candida utilis, rice starch and
kaolin, instead of yeast alone.

Manipulated Yeasts

Techniques towards improving the digestibility and the nutritional composition
of yeast-based diets resulted in manipulated yeast product with good potential
as a substitute for unicellular algae. A preliminary experiment, performed
with Tapes philippinarum at a Spanish commercial hatchery, revealed that 80
% replacement of the algal control diet by the yeast product yielded a daily
growth rate of upto 93 % of that obtained in the algae-fed controls over a 4-
week culture period (Coutteau and Sorgeloos, 1993). The above authors
demonstrated in C.gigas seed that replacing 80 % of the algal diet with
manipulated yeast product gave an average daily growth rate of 70-80 % of
that obtained in the algal control treatments during a three week study. These
studies showed that the use of manipulated yeast diets as partial replacement
to live microalgae diet gave a slower growth rate when compared with the
controls. The authors stated that instead of dried yeast, use of manipulated
yeast diet with improved digestibility and nutritional value has considerable
potential as a low cost partial substitute for live algae in bivalve seed production.

Conclusion

In conclusion, it is observed that the main thrust of the nutritional and food
technology research in oyster culture is on the development of more efficient
and less expensive feeds for the seed production in the hatcheries. This is
being tackled either through high density microalgal production, their
preservation and storage or artificial diets of appropriate particle size containing
balanced nutrient content. The results of the above mentioned experimental
studies indicate that the live algae could be partially replaced by dried or
preserved algal paste (Coutteau and Sorgeloos, 1993) and the artificial diets
are used only in a few commercial hatcheries at present. According to Coutteau
and Sorgeloos (1993) live algae could only be partially replaced by dried T.
suecica (upto 25-50%) or preserved algal paste upto 75%.

Cryopreservation of Sperms and D-larvae

Freezing and preserving (cryopreservation) of gametes and embryos are used
in selective breeding and artificial propagation. This technique is already used
in fish farming (Rogan, 1994). Techniques have been developed to cryopreserve
the sperm and D-larvae of bivalves but not the unfertilized eggs. In a preliminary
study Renard (1991) showed that normal C.gigas larvae can be obtained from
frozen-thawed embryos in the presence of methanol and sucrose.

Recent Developments in Oyster Culture

169

Chao et al., (1997) cryopreserved the late embryos and early larvae of
C.gigas and the clam Meretrix lusoria. Survival rates ranging from 62.3 to
75.1 % were obtained in oysters by using a stepwise freezing protocol. Four
hour old larvae/embryos at 28°C were equilibrated in 2 M dimethyl sulfoxide
(DMSO) +0.06 M trehalose plus seawater for 10 minutes at 27°C and were
then cooled to 0°C followed by cooling to -12°C at the rate of l°C/minute and
held at this temperature for 10-15 minutes allowing equilibration after seeding.
Further cooling to -35°C is achieved at the rate of -2°C/minute, allowed for
10-20 minutes equilibration before quenching in liquid nitrogen. After thawing
in a water bath at 28°C they were placed in seawater to remove DMSO. The
swimming embryos exhibited rotary movements following thawing. For
M. lusoria embryos/larvae with the cryoprotectants 2 M DMSO + 0.06 M
glucose, survival rates ranged from 73.3 to 84.2 % by using the above
protocol.

Some success has been achieved with D-larvae of C.gigas and the clam
Tapes philippinarum. Larvae frozen to -196°C at 24 hours from fertilization
have been thawed and reared. In the case of Tphilippinarum the trial was
continued to 10 days beyond metamorphosis (Utting, 1993). Cryopreservation
is expensive and it may be some time before it is routinely used in the bivalve
hatcheries (Burnell, 1994).

Use of Chemicals to Enhance Spat Settlement

A critical phase in the life history of the oyster is settlement and metamorphosis
as spat. Successful settlement and subsequent survival results in increased spat
production. When ready to set, the pediveliger larvae exhibit “swim-crawl”
behaviour and become “behaviourally competent” to respond to simulation
for settlement (Coon et al., 1990). They crawl on the surface exploring its
suitability, and unattractive surfaces do not sufficiently stimulate the larvae to
settle and undergo metamorphosis. They resume swimming, further exploring
the settling surfaces. The larvae are known to postpone metamorphosis for
several weeks if conditions are not favourable (Loosanoff and Davis, 1963).
Coon et al. (1990) found that cultured larvae of C.gigas could remain competent
while delaying metamorphosis for at least 30 days.

In the oyster hatcheries, 10-30 % of larvae are reported to set as spat
(Wong, 1994). The settlement rate can be increased between 70 and 90 % by
exposure to appropriate concentration of neuroactive compounds such as
epinephrine, nor-epinephrine, L-Dopa and GABA (Coon et al., 1985, 1986;
Wong, 1994). Addition of epinephrine and nor-epinephrine at concentrations
of 1 04- 1 05 M induces oyster larvae to settle and metamorphose (without
settlement surface) as cultchless spat (Coon etal. (1986). Haws and DiMichele
(1993) described a modified procedure for the use of epinephrine which
consistently induced metamorphosis in 90 % of C.gigas and C.virginica.
Epinephrine is first dissolved in a solution of 0.005 N Hydrochloric acid made

170

Oyster Biology and Culture in India

with distilled water and then added to seawater (104M) as described by Coon
et al., (1986). Ascorbic acid (102M) is added to prevent oxidation of the
epinephrine and the pH of the epinephrine-seawater solution is adjusted to 8.0
with NaOH. The oyster larvae are treated in this solution for 4 hours in the
dark. After treatment they are collected in a sieve and returned to the rearing
containers. Maximum response to metamorphosis was similar for both the
oyster species (93-96.8 %) and the time at which this occurred varied between
24-108 hours for different cultures. The mortality rate between epinephrine
treated larvae and control was similar and the final survival rate was highly
variable between cultures (30.9-84.9 %). The mechanism by which epinephrine
acts to induce metamorphosis is not known and no short term detrimental
effects of epinephrine was observed (Haws and DiMichele, 1993).

It is held by oyster biologists that a surface film is developed on the cultch
when held in the seawater and this film enhances the settlement of oyster
larvae. Weiner et al. (1985) studied a bacterium first isolated from C.virginica
hatchery tanks. The bacterium, Shewanella colwelliana when attached to a
surface such as an oyster shell produces L-3, 4-dihydroxy phenyl alanine (L-
Dopa), other melanin precursors and melanin which enhances settlement of
C.virginica (Weiner et al., 1985, 1989). Similar observation was made on the
larval settlement of C.gigas and O.edulis (Fitt et al., 1990; Tritar et al., 1992).

REMOTE SETTING

The development of hatchery technology for oyster seed production paved the
way for the expansion of oyster culture into new cultivable areas where no
natural stocks were available or natural spatfall was poor. Initially the set
larvae (spat) on cultch were transported from hatchery to culture site. But this
procedure necessitated large consignment space which significantly raised the
transportation costs. Further the maintenance of larvae till the spat stage
suitable for transportation, increased the production cost in the hatchery.
Remote setting is a solution to this problem.

Remote setting is the method by which eyed or pediveliger larvae are
transported without water, in moist condition to distant places where they are
set on the cultch material. The use of this technique has revolutionized oyster
culture on the west coast of the USA where seed production is no longer a
problem (Chew, 1991). Significant results were obtained by Henderson (1982)
in larval transport and distant setting of C rassostrea gigas and Gibbons (1988)
in C.virginica.

Prior to shipment the eyed or pediveliger larvae in the rearing tank are
collected on a 280 pm screen, wrapped in nylon cloth and moist paper covers,
to prevent dehydration. Between 7-10 million larvae are packed in a gauze
cloth bag of the size of a baseball, placed in a small cooler and kept moist with
ice packs for transport up to 7 days. The temperature is maintained at 2-5°C

Recent Developments in Oyster Culture

171

during transport (Chew, 1991) . On reaching destination, the larvae are released
in setting tanks containing seawater at 20-25°C. Aeration is provided to
promote even dispersal of larvae and the tanks are usually covered during
setting. Different types of cultch materials for attached spat and oyster or clam
shell chips of 5-6 mm size for single spat are introduced into the setting tank.
Larval density of 150 nos/shell cultch was recommended by Jones and Jones
(1988) to get 10-20 spat/shell. The larvae are fed with live microalgae or
stored algal paste. After setting is complete the cultch is transferred to the
nursery.

In India, Unnikrishnan et al (2001) studied the remote setting of
Crassostrea madrasensis larvae produced in the Shellfish Hatchery of CMFRI,
Tuticorin. The pediveliger larvae were transported to Cochin in moist condition
at 27 ± 1°C and 32 ± 1°C temperatures. The transportation time from Tuticorin
to Cochin was 1 8 hrs. In the larvae transported under the above two temperature
regimes, the survival rate was 100% after 24 hrs rearing in the settlement
tanks. The settlement rate was 61-68%. The survival of the post-set spat after
25 days of rearing was 66.2 to 73.4% in 30 ppt salinity and 71.3% to 87.5%
in 15 ppt salinity. Higher settlement rate and post-set survival was reported in
larvae transported at the lower temperature of 27 ± 1°C than at the atmospheric
temperature of 32 ± 1°C (Unnikrishnan et al, 2001).

In temperate countries the oyster larvae in moist condition are transported
at about 5°C temperature but in India larval transport at 27 ± 1°C (that is 5°C
below atmospheric temperature) was found to be effective. From Malaysia,
Wong (1994) reported that the eyed larvae of C.belcheri kept at 5°C performed
worse than the controls and at 15°C the performance of the eyed larvae, held
up to 72 hrs was either equal or better than the control.

In the USA, farmers usually get 20-30% of the larvae of C.gigas setting
as spat (Henderson, 1982; Roland et al, 1989); in some cases as high as 80%
spat set on cultch material has been reported (Chew, 1991). For the same
species, Holliday et al (1991) have reported 68% spat set, after cold storage
of larvae at 1 1°C for 98 hrs and 77-85% spat set for Saccostrea commercialis.
The results obtained in India with regard to setting rate of larvae compare
favourable with the above results but the duration of the transport of larvae
was only 18 hrs and there is need for further studies to standardise the
techniques of remote setting for long distance transport involving 2-3 days
journey. Roland et al (1989) observed that the proportion of larval setting was
affected by water circulation rate, temperature, salinity, cultch type and feeding
rate.

The technique involved in remote setting is simple and has tremendous
potential, particularly for the cultivation of triploid oysters for which the seed
is raised in the hatcheries. The advantages in the farming of triploid oysters are
given later in this chapter.

172

Oyster Biology and Culture in India

NURSERY REARING OF SPAT

Oyster larvae settle as spat between 300-400 pm size and nursery rearing is
necessary to ensure good survival of the spat until they are large enough to
withstand some competition and smothering effects of silt (Matthiessen,
1989). Nursery rearing is carried until the spat grow to 20-25 mm size.

Many hatcheries have nursery facilities and the cultched seed are usually
grown in raceways through which filtered seawater is circulated. The single
spat, immediately after settlement are reared in upwelling systems. They may
be land-based or located in an estuary. The former consists of flow-through
troughs or ‘upwellers’ (Bayes, 1981). Upweller systems consist of containers
provided with a screen as bottom (silos) containing oyster spat. The silos are
held inside a large container in such a manner that seawater enters through the
screen at the bottom, flows upward through the oyster spat producing a semi-
fluidised bed of spat, and discharged usually through a side exit pipe (Bayes,
1981; Spencer et al, 1986). The passage of plankton rich seawater through the
oyster seed assemblage allows them to be held in large numbers and at the
same time permits rapid growth, and discourages fouling and clumping of spat
(Castagna et al, 1996). Several silos are arranged in each upwelling unit.
Seawater filtered through a 45 pm mesh is used so that naturally occurring
algae are available as food and flow rate of 20-50 ml/minute/gram spat is
recommended (Utting and Spencer, 1991). There are different types of upwellers
and some are vertical pipes or cylinders of 15-20 cm diameter and individually
plumbed so that water can flow from the bottom to outside on the top with
oyster seed loosely packed within the water column.

Utting and Spencer (1991) described an upwelling recirculation nursery
system for spat. It consists of 10 tubes loaded with 60 gram spat biomass/tube.
Seawater flow rate is 20-30 ml/minute/gram live weight, i.e. 1.5-1. 8 1/minute/
tube. The air lift system raises about 18 1/minute to the header tank. Optimum
recommended daily food supply for 600 g biomass (10 tubes x 60 g) is equal
to 171 1 of Tetraselmis equivalents at 1 million cells/ml (equal to 3 feeds of 57
1/day). This works out to 34 g/day of spray-dried algae. The water is changed
three times per week.

Apart from shore based upwellers, systems are also designed for operation
on rafts or floats to be deployed in bays or estuaries (Bayes, 1981; Baldwin et
al, 1995).

In the nursery rearing of spat, these upwelling systems ensure control over
the predators and foulers resulting in greater survival of the spat. The present
system followed in India wherein the oyster spat are reared in synthetic mesh
bags, suspended from racks in the Tuticorin bay is cost effective with reasonably
good survival (Figure 27).

Recent Developments in Oyster Culture

173

PROBIOTICS

The word Probiotic is used as promoter of life and is opposite of the word
antibiotic. For livestock and poultry, a number of commercial preparations are
available to promote colonization of desirable bacteria in the gut. In aquaculture
the use of probiotics is relatively recent and commercial use is mostly confined
to shrimp farming.

Several definitions of probiotic are available. Fuller (1989) defined it as
“a live microbial feed supplement, which beneficially affects the animal by
improving its intestinal microflora” while Havenaar and Huis int Veld (1992)
called it as “a mono or mixed culture of live micro-organisms when consumed
by an animal or man, affect beneficially by improving the properties of the
indigenous microflora of the gut”. Tannock’s (1997) version of probiotics is
“live microbial cells administered as dietary supplements with the aim of
improving health”. A more recent version of the definition of probiotics is
“microbial cells that are administered in such a way as to enter the
gastrointestinal tract and to be kept alive, with the aim of improving health”
(Gatesoupe, 1999). The probiotics are expected to perform the following
functions: a) antagonism to pathogens, b) gut colonization with possible
adhesion to intestinal mucus and c) increased resistance of the host to the
pathogens (Gatesoupe, 1999).

Douillet and Langdon (1994) found that addition of the bacteria (strain
CA2) as a food supplement to xenic larval cultures of Crassostrea gigas
consistently enhanced the growth of larvae during different seasons of the
year. Addition of CA2 bacteria at 105 cells/ml to cultures of algae Isochrysis
galbana (ISO), /. aff. galbana (T-ISO) or Pseudoisochrysis paradoxa (VA-12)
fed to C. gigas larvae increased larval growth, the proportion of larvae that set
to produce spat, and the subsequent size of the spat. These authors suggested
that addition of CA2 bacteria may provide essential nutrients not present in the
algal diets or improve their digestion by supplying digestive enzymes to the
larvae. They have recommended supplemental feeding of bivalve larvae with
CA2 bacteria in the hatcheries to enhance production and stressed the need for
further research in this area.

Gibson et al. (1998) stated that, the probiotics in part inhibit the pathogens
by producing substances and these inhibitory agents are called bactereocin-
like inhibitory substances (BLIS). These authors assessed the ability of BLIS
producing Aeromonas luedia (strain A 199) to act as a probiotic on C. gigas
larvae. When A 1 99 strain alone was added, the viability of the larvae was not
significantly different from the controls. On the other hand, when only Vibrio
tubiashii was added there was heavy larval mortality between day 3 and 5.
Addition of V.tubiashii followed by the introduction of A 199 showed a
significant difference between the ‘viability of the larvae w hen compared with
the larvae in the control and the larvae inoculated with only probiotic A 199
strain.

174

Oyster Biology and Culture in India

Riquelme et al (1996) found significant improvement in the survival of
scallop larvae after preliminary treatment with Alteromonas haloplanktis for
one hour followed by challenge with Vibrio anguillarum. According to
Gatesoupe (1999), these authors assumed that the probiotic strain produced
inhibitory substances that blocked bacterial growth in the larval rearing medium,
including growth of the probiotic itself (autoinhibition).

Reviewing the use of probiotics in aquaculture, Gatesoupe (1999) has
drawn the following conclusions. The application of probiotics is successful
in terrestrial animals; it is promising in aquaculture and needs considerable
research input. Some bacterial strains may increase the survival of bivalve
larvae when they are introduced into the rearing medium (Riquelme et al.,
1997), probably as food supplement (Douillet and Langdon, 1994). In many
studies the fate of the probiotic in the rearing medium and in the gastrointestinal
tract is not answered. Immunological and molecular probes are useful tools to
trace the probiotic cells.

GENETICS

Considerable research has been carried out on the application of genetics for
the improvements in the production of bivalves, particularly on oysters.
Newkirk (1980) gave a review of genetics and potential for selective breeding
of bivalves. Since then there were a large number of studies and recently
Gaffney (1996), Longwell and Stiles (1996) and Newkirk (1996) dealt on
oyster genetics while Sheridan (1997) gave an excellent review on genetic
improvement of oyster production.

Quantitative Genetics

Genetic Parameter Estimates: Newkirk (1996) stated that the relative
importance of the genetic variance is often expressed as a ratio of the genetic
variance to the total phenotypic variance (which is composed of the genetic
and environmental components). This ratio is called the heritability.

In Crassostrea gigas , Lannan (1980) obtained full-sib variance component
heritability estimates of 0.31 ± 0.06 for larval survival and 0.09 ± 0.08 for
setting success, and at 18 months of age, 0.33 ±0.19 for total weight, 0.32 ±
0.30 for shell weight, 0.37 ± 0.20 for wet meat weight and 0.46 ± 0.22 for the
wet meat to total weight ratio. In the same species Hedgecock et al (1991)
estimated the half-sib variance component heritability for wet meat weight at
commercial harvest size to be approximately 0.20. They stated that non¬
additive genetic variations could be important for this trait, and a sex effect
resulted in female oysters being around 10 % heavier than male oysters.

In C.virginica , Newkirk et al (1977) reported full and half-sib variance
component heritability estimates of 0.09 to 0.5 1 at 6 days of age and of 0.50
to 0.60 at 16 days of age for growth rate.

Recent Developments in Oyster Culture

175

In Ostrea edulis , Toro and Newkirk (1990) obtained offspring/ mid-parent
regression heritability estimates of 0. 14 ± 0. 12 and 0.24 ± 0.20 for live weight
and 0.11 ± 0.04 and 0.19 ± 0.07 for shell weight after one and two growing
seasons respectively (i.e. at 6 and 1 8 months of age). Offspring-parent regression
estimates of genetic, phenotypic and environmental correlations between the
above two traits were 0.96, 0.85 and 0.84 respectively after one growing
season and 0.99, 0.74 and 0.67 respectively after two growing seasons. These
authors found the genetic and phenotypic correlations between the first and
second growing seasons for the same trait as 0.72 and 0.48 respectively for
live weight and 0.75 and 0.70 respectively for shell weight. The authors have
subjected the oyster population to one generation of divergent selection for
live weight after one growing season.

After reviewing the heritability estimates in oysters, Sheridan (1997)
stated that they indicate selection in oyster populations for increased growth
rate and increased disease resistance should be successful. He cautioned that
they should be taken as a very rough guide as to the possible selection
response, and these heritability estimates have high standard errors.

Selection: Selection is the process wherein the individuals that have
superior performance are bred, resulting in a genetic change in the stock.
Selection saves certain genotypes and removes others. The information needed
for selection include a) the heritability of the traits concerned, b) the correlation
(both phenotypic and genotypic) between traits and c) the relative economic
value of various traits if more than one trait is considered (Newkirk, 1996).
The important traits focused in the oyster breeding programmes by researchers
are growth, survival and resistance to disease. Newkirk (1988) highlighted the
importance of sampling widely prior to commencing a breeding programme.
Most of the studies on oyster selection were made on growth rate and live
weight and a few studies were conducted on selection for resistance to disease.

The results of a study on selection for increased live weight for one
generation of C.virginica were reported by Haley and Newkirk (1982). The
parents studied were 2,3 and 4 years old oysters and a control population. The
offspring of 3 and 4 year old oysters were significantly heavier at 27 months
of age than the control line progeny, indicating that selection should be
effective in improving the growth rate. Paynter and Dimichele (1990) compared
the linear growth rate of C.virginica between the native population and a line
originally derived from this population and selected for improved growth rate
for 18 generations by an oyster farmer. The selected oysters had a higher
growth rate of 28 % in the first and 24 % in the second growing seasons when
compared to the native oysters.

Haskin and Ford (1988) and H.H. Haskin (pers comm, to Sheridan, 1997)
selected C.virginica for resistance to MSX parasite, Haplosporidium nelsonii
and found that selected strains have survival rates upto 10 times when compared

176

Oyster Biology and Culture in India

to the control lines. This selection study was conducted for five generations.
It is suggested that inbreeding had no detrimental effect on survival ol the
selected strain. In a study, C.virginica derived from the Delaware Bay-selected
oysters and maintained at a commercial hatchery on Long Island were compared
to an MSX susceptible stock from Long Island in growth trials in Massachusetts
(Matthiessen et al., 1990). The authors found that Delaware oysters grew
faster than the Long Island oysters and the resistance to MSX was confirmed.

From a study by Haley and Newkirk (1982) on the European oyster
Ostrea edulis, after one generation for selection for four lines of oysters, the
estimated heritabilities for increased live weight at about two years of age
were 0.39, 0.47. 0.47 and 0.72. Newkirk and Haley (1983) in their study on
the live weight of the same oyster species in the second generation realized
heritability of 0.16, 0.17, 0.20 and 0.22 (Sheridan, 1997).

Hershberger etal. (1984) have shown that in C.gigas selection has improved
resistance to summer mortality. After three generations of selection, cumulative
mortality was around 20 % while in the control 62 % mortality was observed.
In oyster culture carried in the temperate waters, these results are significant
as summer mortalities are a matter of concern.

In Saccostrea commercialism Nell et al. (1996) found that after one
generation of selection for increased live weight, two of the four selection
lines were significantly heavier (P< 0.05) than two control lines.

Inbreeding , Heterosis and Heterozygosity: Following Sheridan (1997)
this section on inbreeding is considered together with heterosis and
heterozygosity since there were very few studies on deliberate inbreeding in
oysters and also the oyster inbreeding studies examined the effect of inbreeding
by comparing the performance of the inbred lines with their crosses. Inbreeding
is the crossing of individuals of close relationship. It reduces genetic variation,
increases homozygosity and as a result deleterious recessive genes find
expression, leading to decreased fitness of oyster (Newkirk, 1996). This is
known as inbreeding depression.

Out of six studies conducted on the American and Pacific oysters on the
effects of inbreeding, in one study (Lannan, 1980) only the inbred stock was
found to be superior to outbred stock (Sheridan, 1997). Lannan (1980) subjected
C.gigas to two generations of full-sib matings and stated that on an average,
the inbred larvae had higher survival (0. 165 %) than the outbred larvae (0. 100
%) and this difference was highly significant. In the remaining five reports,
inbreeding did not improve the performance of the desired traits in the oysters
and in comparison, the performance of the outbred lines was generally better
(see Sheridan, 1 997).

Oysters have, extremely high progeny numbers (upto 25 million larvae
per mating as reported by Holliday, 1992) and could be expected to maintain
a higher level of heterozygosity than that predicted from the effective population

Recent Developments in Oyster Culture

177

size. Sheridan (1997) wrote “This expectation is due to these large progeny
numbers containing all possible gene combinations (even for tightly linked
genes) thus providing natural selection with considerable scope to favour the
(perhaps small proportion of) individuals fortunate not to be homozygous for
deleterious recessive genes". Comparison of heterozygosity levels estimated
from parent numbers and from protein electrophoresis by Smith et al. (19S6)
for the Pacific oyster, Dillon and Manzi (1987) for the hard clam Mercenaria
mercenaria and by Vrijenhoek et al. (1990) for the American oyster, showed
this to be the situation. Sheridan (1997) considered this as a possible reason
why outbred lines were not always superior to inbred lines.

Positive correlation between heterozygosity and the growth rate and/ or
live weight were reported by several authors. Singh and Zouros (1981) found
such a relationship for seven electrophoretically detectable loci in one year old
American oyster. Four of the loci studied had three alleles. Out of fifteen
heterozygotes, fourteen showed overdominance for growth rate. Foltz et al.
( 1983) reanalysed the data of the above authors and found that heterozygosity
at these levels accounted for 4 % of growth variability and there was no
evidence of epistasis. A study was conducted by Hu et al. (1993) on the effect
of a polymorphic enzyme on survival and shell size at about three months after
metamorphosis in one of Haskin and Ford’s (1988) American oyster disease
resistant selection lines. The results indicated that juvenile oysters, heterozygous
for this locus possessed a significantly (P < 0.05) greater survival and tended
to be larger than the corresponding homozygotes.

Zouros and Mallet (1989) reviewed the experimental evidence for the
presence of a positive association between growth rate and heterozygosity in
marine molluscs. They stated that populations with a heterozygote deficiency
are also likely to show a positive association between the growth rate and
heterozygosity. The review of the experimental evidence by these authors
indicated that a heterozygote deficiency iu marine bivalves tended to decline
(and in some cases disappear) as the population aged. They have noted that
none of the genetic explanations were consistent with the experimental evidence
reviewed by them and they tended to favour the associative overdominance
hypothesis (AOH) which does not involve overdominant gene action.
Associated overdominance is attributed to linkage disequi 1 ibria between genes
affecting the trait apparently influenced by overdominant gene action (i.e.
growth rate) and deleterious recessive genes entering the population by mutation
(Sheridan, 1997). Hu et al. (1993) also favoured the AOH as the most likely
reason for their results. The AOH is consistent with the experimental data
from both plants and other animals and suggests that true overdominance is
not an important property of the genes (Falconer, 1981). Sheridan (1997)
stated “A positive association between heterozygosity and growth rate in
conjunction with a heterozygosity deficiency that declines as a population

178

Oyster Biology and Culture in India

ages could be due to the faster growing individuals having a poorer fitness
during the larval stage and a better post-setting fitness.” A positive association
between heterozygosity and both growth rate and survival is also a common
consequence of crossbreeding (Sheridan, 1981).

The strategies adopted for improving cross bred performance are:
inbreeding and retaining the better nicking lines, reciprocal recurrent selection
and within line selection, whilst also retaining the better nicking lines (Fairfull,
1990). For improved cross bred performance, Bell (1982) and Wei and Van
der Steen (1991) recommended a combination of within line and reciprocal

recurrent selection. Sheridan (1997) wrote “ . the improving performance,

of the crossbred population over successive generations of within line selection
is a combination of the improving performance of the parent lines and the
increasing heterosis in the cross between them”. Mallet and Haley (1984)
reported substantial reciprocal mating effects for heterosis (or hybrid vigour);
this highlights the importance of examining the performance of both reciprocal
matings for all crosses before determining the male and female parent lines to
be used in producing the crossbred market oyster.

Environmental Variability and Oyster Growth Rate: In tray-grown oysters
it is well known that the growth rate is sensitive to apparently small
environmental differences due to their location within the tray (Sheridan et al.
1996). An oyster production system specially developed to minimize (if not
eliminate) any competition between neighbouring oysters for evaluating the
performance in genetic studies was developed by Sheridan et al. (1996). In
oyster genetics, consideration should also be given to the possible impact of
the genotype by environmental interactions on oyster productivity.

Conclusion: Reviewing the work on oyster genetics, Sheridan (1997)
wrote “Thus the application of the genetic improvement techniques so
successfully, applied to other livestock species should also be successful in
producing more productive oyster stocks.”

In oyster breeding programme, within line selection of oysters with traits
which are economical, important and amenable to selection, are to be taken.
The selection method for each trait will depend upon its heritability and the
cost of rearing the pedigreed families. The performance of pure strains and
their reciprocal crosses should be assessed. Also selection lines should be
evaluated under standardized environmental conditions at a stocking density
that preclude competition between neighbouring oysters. With a view to take
advantage of hybrid vigour, the oyster should be a cross between different
selection lines (Sheridan, 1997).

Chromosomal Engineering

Fifteen species of Crossostrea, six species of Ostrea and three species of
Saccostrea studied by various authors have a haploid number of 10
chromosomes (see Longwell and Stiles, 1996). In the Pacific oyster the

Recent Developments in Oyster Culture

179

diploid complement (2 n) of chromosomes is 20, in triploids 30 and in
tetraploids 40. Exact multiples of haploid set of chromosomes are known as
euploids eg: diploid, triploid. Any deviation from the euploid number is
classified as aneuploid. For example oysters with 2 n+1 chromosomes (total
21) or 2 n-1 (total 19) are called aneuploids. There is no evidence of sex
chromosome pair in oysters (Longwell and Stiles, 1996). Bivalves are
particularly amenable to various forms of chromosomal manipulations. Diploid
females usually spawn tetraploid eggs (four sets of chromosomes per cell, 4
n) which after interaction with haploid (1 n) sperm, undergo sequential
reductions in maternal chromosome number (4n to 2n and 2 n to In ) through
release of the first (2 n) and second (In) polar bodies (Ward et al. 2000).

Triploidy and Tetraploidy: Triploid oysters were first produced in the
early 1980’s (Stanley et al., 1981). Triploid oysters have several advantages
over diploids and Crassostrea gigas production by aquaculture using triploids
approximately accounts for one third to one half from the Washington State
alone (Chew, 1994).

Triploidy induction: Allen (1987) and Beaumont and Fairbrother (1991)
reviewed the methods used by workers to induce triploidy in bivalves; they are
produced by inhibiting the extrusion of second polar body immediately after
fertilization. To achieve this, treatments with chemicals, pressure, temperature
and electric impulses are applied. Also mating of diploids with tetraploids
results in triploids.

Scarpa et al. (1994) used 6 methods, some of them combinations, to
induce triploidy in the mussel, Mytilus galloprovincialis . The agents used are
cytochalasin B (CB at 1 mg /l), heat (HT:30°C), Calcium chloride (CA:0.1M),
combined exposure to CA 0. 1M and heat 30°C (CAHT), Caffeine (CF: 15mM)
and combined exposure to 15mM Caffeine and heat 30°C (CFHT). They were
applied 20 minutes after sperm addition so as to suppress polar body II
formation, and left for 15 minutes. Calcium treatment was least efficient (4.7-
7.5%) in inducing triploidy. The other 5 agents on an average induced 86%
(CB), 81% (HT&CFHT), 73% CAHT and 71%(CF) triploids. The proportion
of D-larvae of 48 hr was reduced in all the treatments, being least reduced by
CB and most reduced in CAHT. The authors concluded that CB is the most
effective among the methods used and heat treatment is the second alternative.

Cadoret (1992) used a microslide electrofusion chamber to test different
field strengths, durations and number of electrical pulses on the viability of 2-
cell oyster and mussel embryos. Then by applying the most promising
parameters to fertilized eggs in a larger chamber, triploid production went up
to 55% and 36% and tetraploids up to 20% and 26% for oysters and mussels
respectively.

Desrosiers et al. (1993) induced triploidy in the Pacific oyster C. gigas ,
scallop Placopecten magellanicus and mussel M.edulis by using the chemical

180

Oyster Biology and Culture in India

6-dimethylaminopurine (6-DMAP). The highest percentage of triploids
produced in the oysters was 90%, in scallops 95%, but larger exposure
interfered with cleavage and resulted in abnormalities, particularly in the
mussel. Triploid larvae of the three bivalves showed higher mortality rates
than the control diploids. Gerard et al. (1994a) treated C.gigas with 6-DMAP
and also Cytochalasin B (CB). Survival to D-stage was inversely related to 6-
DMAP concentration and the percentage of triploids was shown to be 6-
DMAP dose dependent. The optimum treatment was found to be 450 p mol
/ 1 of 6-DMAP beginning 15 minutes after fertilisation over a 10 minute period
yielded a mean of 85% triploidy production; the mean survival to D-larval
stage was 64%. Treatment with lmg / 1 of CB, 20 minutes after fertilisation
over a 15 minute period yielded a mean production of 95% triploids and the
mean survival to D-larvae was only 36%. According to Gerard et al. (1994 a)
the advantages of 6-DMAP over CB are : a) 6-DMAP is not carcinogenic, b)
it is cheaper, c) water soluble and easy to use and d) gives higher production
of D-larvae.

Nell et al. (1994) induced triploidy in S accostrea commercialis by CB
treatment and obtained 84% success rate. Hand and Nell (1999) succeeded in
inducing triploidy in 88% of S. commercialis by CB treatment. Treatment with
CB or with 6-DMAP is commonly followed in commercial hatcheries by
inhibiting the extrusion of second polar body (Eudeline et al., 2000). Guo et
al. (1996) listed the following as disadvantages of the CB method: a) Induction
of triploidy is not 100% effective and the success rate is about 80% in
commercial hatcheries. Success rate < 80% is a problem for hatchery
management resulting in waste of effort, b) CB is toxic and the health and
safety of hatchery personal is a matter of concern and c) The blocking of polar
body 2 may result in lower survival and slower growth in the triploids.

Guo et al. (1996) suggested that the above disadvantages can be avoided
if triploids are produced by mating tetraploids with diploids. Guo and Allen
(1994 b) produced viable tetraploid C.gigas and reared them to sexual maturity
for the first time in a mollusc. They blocked the polar body 1 in eggs from
triploid, fertilised with normal haploid sperm. Tetraploid C. gigas matured at
one year of age with close to normal sex ratio and fecundity. Garnets produced
by the tetraploids are fully functional in terms of fertilization, meiosis and
chromosome segregation. Guo et al. (1996) noticed that the sperm from the
tetraploids were less motile than normal sperm of the diploids but possessed
high fertilization rates in many replicates. Out of 710 C.gigas sampled by the
mating of tetraploid and diploid oysters, all were triploids except one (0.1%)
which happened to be a tetraploid. The authors stated that it may be due to
spontaneous failure of releasing polar body 2 in a normal egg fertilised by a
diploid sperm. In a concurrent study with the above, Guo et al. (1996)
obtained 46% triploids by CB treatment in C.gigas. Guo et al. ( 1 996) concluded

Recent Developments in Oyster Culture

181

that “ triploid production by mating tetraploids and diploids is as simple as
producing normal diploids, and no artificial treatment is required”. The mated
triploids were found to be as viable as normal diploids; they appeared to show
polyploid gigantism, an advantage in aquaculture.

In India, triploid oysters (C .madrasensis) have been successfully produced
using physical and chemical stimulants, (CMFRI, 2001) by arresting the
release of second polar body. Exposure of oyster embryos to 6- DMAP at
concentration 100 mM for a period of 8 minutes commencing from 15 minutes
post-fertilization was found to be optimum for triploidy induction. For
Cytochalasin B, the optimum dosage was 0.05 mg/1 concentration for one
minute. Application of cold shock at 5 °C for 10 minutes, and heat shock at
37°C for 5 minutes were also found to be optimum for producing triploid
oysters. Karyological examination has revealed 30 chromosomes in triploids
as against 20 in the diploid controls. Highest triploid induction of 63% was
obtained in 100 mM treatment with 6 - DMAP for 10 minutes. The triploid
spat of C. madrasensis registered a growth rate of 5.53 mm / month (for 6 -
DMAP treated), 5.8 mm (for cold induced) and 5.5 mm for the control.

Methods to detect triploidy: Three methods are in vogue to determine
polyploidy in bivalves namely chromosome counting technique, flow cytometry
and microfluorometry. Apart from these Gerard et al. (1994 b) used a method
known as ‘Image analysis’ while Child and Watkins (1994) developed a
simple method based on the measurement of cell nucleus diameter to detect
triploids.

Chromosome counting technique: The number of triploids produced is
usually estimated at the embryo stage by counting chromosomes. This technique
when applied to later stages requires the use of cytotoxic chemical, Colchicine;
it is also slow and tedious.

Flow cytometry: This was described by Chaiton and Allen (1985). It is
used to estimate the number of triploid cell nuclei obtained from gill tissue and
haemolymph (Allen 1983) and larvae (Downing, 1989). This equipment is
very expensive and is not widely available (Child and Watkins, 1994).

Microfluorometry : The essential equipment used in this method is also
expensive. Komaru et al (1988) determined triploidy in scallop C hlamys
nobilis by DNA microflurometry with DAPI staining.

Image analysis : This method is routinely used in medical check-ups to
determine the ploidy level of cancerous cells. Gerard et al. (1994 b) applied
this method to detect triploidy in C.gigas, O.edulis and the clam Ruditapes
philippinarum. They concluded that image analysis technique appears to be a
very efficient method for ploidy determination in bivalves. This technique is
cheaper than flow cytometry but expensive when compared to microfluorometry
(Gerard et al ., 1994 b).

182

Oyster Biology and Culture in India

Measurement of nucleus diameter: This method assumes that the nucleus
of a triploid bivalve is approximately spherical and 1.5 times greater in
volume when compared with diploid nucleus due to additional DNA content.
A sample of gill tissue or haemolymph cell nuclei are stained and measured.
In the Manila clam, Child and Watkins (1994) found the ratio of diploid DNA
content to triploid DNA content as 1:1.51 which is close to the theoretical
value of 1:1.5.

Advantages of triploids: Nell et al. (1994) have reported that triploid
S.commercialis were on average 41% heavier in whole weight than diploids
after 2.5 years of growth. The triploid oysters also maintained higher dry meat
weight and higher condition index values than their diploid siblings at all sites
during the final 10 months growth to market size. The same authors summarized
the growth performance (% whole weight increase) of triploid C.gigas, C.
virginica and S. commercialis over diploids recorded by various authors. The
triplods were 23 to 71% heavier than diploids between 5 to 3 1 months growth.
Triploid C.gigas had growth advantage of about 23% over diploid controls in
2-3 year olds. Also the former maintained meat condition while diploids, due
to spawning were not marketable for several months (Ward et al., 2000). Hand
and Nell (1999) stated that in two years, S.commercialis triploids of smaller
size grade grew 35.6% faster in whole weight and the larger grade 56.6%
faster when compared to diploids of corresponding grades in initial size.
Growth advantage of triploid C.gigas was most obvious at 8 months post¬
fertilisation and 2 months before sexual maturity. At this time triploid oysters
were 35-51% larger than normal diploids (Guo et al., 1996). In the polyploid
gigantism in molluscs there is no cell number compensation so that larger cells
in the polyploids will generally result in larger body size (Guo and Allen, 1994
b). Thus the main advantages of triploid oysters over diploids are summarised
below:

• The gonad is not well developed resulting in relatively steady condition
index which enables year round marketing (Allen, 1988).

• Reduced gonad development results in higher growth rate and more
meat yield, although only under favorable conditions (Davis, 1989).

• Due to low fecundity, triploids have also been used for population
control and biological containment of non - native species (Guo and
Allen, 1994 a).

Aneuploidy: Cytogenetic abnormalities such as aneuploidy are known to
be common in bivalves and aneuploidy has also been observed in triploid and
tetraploid oysters ( see Leitao et al, 2001). This phenomenon which usually
originates from non - disjunction of chromosomes during mitosis or meiosis
is mostly lethal in higher animals like mammals or results in growth retardation.
But it is less deleterious in lower animals and plants. A negative correlation
between somatic aneuploidy and growth rate has been reported in the offspring

Recent Developments in Oyster Culture

183

of cultivated C.gigas (Thiriot - Quievreux et al. 1988, 1992) and in natural
populations of the same species (Zouros et al., 1 996). In 1 3 diploid populations
of C.gigas studied by Leitao et al (2001) between 1988 to 1999, slow-
growing oysters always showed higher levels of aneuploidy than the fast
growing oysters in all the cultivated and natural populations. Such growth
retardation of aneuploids was not observed in triploid and tetraploid C.gigas
(Guo and Allen, 1994 b; Wang et al., 1999).

Wang et al. (1999) observed that triploids produced by mating tetraploids
and diploids produced 20% more aneuploids than the triploids produced by
blocking the second polar body of the fertilized eggs of diploid C.gigas
(2.2%). The authors suggested that the Pacific oyster can tolerate aneuploidy
by 5-10% of the genome, i.e. 2n±l,3n±3 and 4 n ± 2 where n=10. Wang
et al. (1999) concluded that with or without aneuploids the diploid and
tetraploid cross oysters (triploids) grow faster than the triploids produced by
chemical treatment.

The reasons for the relationship between growth and aneuploidy are not
yet known but a genetic basis (Zouros et al., 1996), environmental factors
such as pollution (Dixon, 1982) and viral diseases (Maroun et al., 1986) were
suggested.

Biotechnological Approaches

Modern aquaculture is growing through a rapid growth phase stimulated by
the recent develoments in biotechnology and its application. New technologies,
which permit the identification and manufacture of natural products such as
hormones that find application in hatcheries, are being developed. Other
techniques include the introduction of foreign genetic material into oysters to
produce transgenic animals. Newkirk (1996) outlined some of the techniques
that may find application in oyster genetics to increase production. These
include cloning of genes to produce hormones that can be used in the hatchery
to increase seed production, DNA fingerprinting instead of electrophoretic
analysis to study population genetics and production of transgenic oysters.
Researches using these biotechnological tools towards increasing the production
of the oyster are still in the nascent stage of development.

Interspecies Hybridization

Some studies were conducted to hybridize the species of Crassostrea and
often it resulted in failure of fertilization, meiosis or in abnormal development.

Normal fertilization, meiosis and cleavage were reported in the crosses of
C. virginica with C. rhizophorae and also in the crosses of the former with
C.gigas (Menzel, 1973; Stiles, 1978; Scarpa and Allen, 1992). Similar results
were obtained in cross fertilization of C.gigas with C.angulata , a possible
synonym or subspecies of the latter (Menzel, 1973; Carriker and Gaffney,
1 996). In many cases of interspecies hybridization, despite normal cleavage

184

Oyster Biology and Culture in India

the hybrids failed to metamorphose (Longwell and Stiles, 1996). Gaffney and
Allen (1993) reviewed hybridization among Crassostrea species.

Recently Soletchnik et al. (2002) have reported on the hybrids of C.gigas
and C. angulata. After the hatchery and nursery phases the hybrids were
successfully reared for two years and a clear maternal effect was observed for
growth and reproductive characteristics of the hybrids. While Gaffney and
Allen (1993) stated that C.gigas and C. angulata are indistinguishable in terms
of protein polymorphism, karyotype and larval morphology , Heral and Deslous
- Paoli (1991) reported them as two distinct species on the basis of physiological
reproductive characterstics.

OYSTERS AS BIOFILTERS IN AQUACULTURE

During the past decade shrimp farming has grown phenomenally in coastal
areas in the country. However, in recent years, the outbreak of diseases in the
cultured shrimps and the loss of stock is a serious set back. Added to this is
the concern expressed by the environmentalists about the pollution effects due
to the discharge of shrimp pond waste water into the coastal waters causing
eutrophication and increased turbidity.

In the shrimp and fish farms the unused artificial food, faecal matter, and
dead/decaying organic matter results in the production of ammonia. By
nitrification, ammonia is converted into nitrites and nitrates which result in
plankton blooms within the pond and also in the waste water released from the
pond. The oxygen demand in the pond rises since nitrification is an aerobic
process and also the plankton blooms need oxygen. The waste water from the
culture ponds contains high load of suspended particulate matter composed of
detritus, bacteria and phytoplankton; it is also rich in dissolved nutrients.

Several studies were conducted to develop a system of biological filtration
of the shrimps / fish pond waste water by the use of bivalves to reduce the load
of suspended particulate matter, followed by seaweeds to bring down the
concentration of dissolved nutrients so that the health of the environment and
farmed shrimp / fish can be improved. One may call it as an ‘Integrated
farming system’ which is largely sustainable and also brings additional
economic benefits by way of production of bivalves and seaweeds (Appukuttan
and Kripa, 2001). The use of oysters as biofilters is dealt in this section.

Oysters and Shrimp Culture

A study was conducted by Jakob et al. (1993) in Hawaii, USA to assess the
potential of growing the American oyster Crassostrea virginica using marine
shrimp culture pond water in onshore flow through tanks. Cultchless oyster
seed of 0.04 g mean weight, numbering 5000, were stocked in trays held in
310 1 flow through system ( tank Tl) , receiving water at 40 1/minute. In
another 310 1 tank (T2) with 80 1/minute water flow rate, about 2000 oyster
seed of 0.05 g mean weight were stocked. The seawater was drawn into the

Recent Developments in Oyster Culture

185

tanks from the shrimp pond in which semi-intensive culture of Penaeus
vannamei was carried at a stocking density of 15 - 20 nos/m2. After 268 days
the oysters in T1 tank have attained 68 g mean weight and in T2 tank the mean
weight recorded was 78 g. The marketable size of 58 g was attained in 198
days in T1 and 1 83 days in T2 tank. Based on this study the authors concluded
that “...undiluted, semi- intensive marine shrimp pond water provides all the
requirements for the very rapid growth of the American oyster Crassostrea
virginica ...”.

From Australia, Jones and Preston (1999) conducted a study of 2 hrs
duration in water drawn from an intensive commercial shrimp farm stocked
with Penaeus japonicus (35 nos/m2). The shrimp pond water was filled in 34
1 tanks, stocked with 8, 16 and 24 oysters ( Saccostrea commercialis ) of
average 55 g weight. During the two hour study period the water remained
static in the tanks. Filtration of the shrimp pond effluent water by the high
density oysters (24 nos / tank) reduced the total suspended solids to 49%,
bacterial numbers to 58%, total nitrogen to 80% and total phosphorous to 67%
of the initial values. The combined effects of settlement and oyster filtration
reduced the concentration of chlorophyll a to 8% of the initial effluent value.
Except for the bacterial numbers, there was reduction in all the parameters
mentioned above in the two remaining oyster tanks holding 8 and 16 oysters
when compared to the control. The authors suggested that 12 % of the shrimp
pond area may be set aside for oyster filtration and based on 20% water
exchange per day, a 1 -ha pond would need 1,20,000 oysters ( at the same
stocking density used in the high density treatment in this study).

In a laboratory scale study from Australia Jones et al. (2001) evaluated the
effectiveness of a three-stage shrimp pond effluent treatment system. In the
first stage the pond water was collected and allowed to settle for 24 hrs. Part
of this water was transferred to tanks holding oysters S. commercialis and
maintained for 24 hrs, followed by transfer of this water to tanks stocked with
macroalgae Gracilaria edulis for another 24 hrs. The results on the overall
improvement in the water quality after 72 hrs (end of stage 3 of the experiment),
expressed as final percentage of initial concentration were as follows: Total
suspended solids 12% , total N 28% , total P 14% , NH4 76%, N03 30%,
dissolved P 35%, bacteria 30% and chlorophyll a 0.7%. The authors stated
that previous attempts to improve effluent water quality using filterfeeding
bivalves and macroalgae to reduce nutrients have been hampered by high
concentration of clay particles typically found in untreated pond effluent.
These particles inhibit feeding in bivalves and reduce photosynthesis in
macroalgae. They stressed the need for sedimentation of the pond effluent
before it is subjected to biofilteration. Jones et al (2001) suggested combined
culture of oyster and seaweed in the same tank. However, the growth
requirements of each species have to be optimized. Otherwise, more biomass

186

Oyster Biology and Culture in India

may be decaying than that produced, lowering water quality (Jones et al.,

2001).

A study was conducted by Wanninayake et al. (1998) in Sri Lanka on the
use of Crassostrea madrasensis in reducing the suspended solids and
chlorophyll concentration in the effluent water of a semi-intensive shrimp
culture system. Two size groups of oysters, 20-30 cm and 50-60 cm were used
(the sizes given seem to be typographical error and should read as mm instead
of cm). Larger oyster group was more efficient in reducing the suspended
solids and chlorophyll concentration than the smaller group. The efficiency of
the former group was better in 20 ppt than in 30 ppt salinity of the effluent
water. The authors concluded that C. madrasensis can be effectively used to
treat the shrimp pond effluent water to reduce the levels of suspended solids
and chlorophyll concentration.

Hu - jiachai et al. (1995) in a study on shrimp and oyster mixed culture
in shrimp pond, reported that the shrimp yield increased by 30%, and oyster
meat yield increased by 20.3% resulting in high economic benefits.

Oysters and Finfish Culture

Jones and Iwama (1991) conducted a study in the ployculture of the oyster C.
gigas with chinook salmon Oncorhynchus tshawytscha. Oysters of 1-year age
were reared for 5 months in suspended lentern net cages (A) inside salmon net
cages, (B) within the salmon farm but outside the salmon net cages, and (C)
the controls in a commercial oyster farm, 4-6 km away from salmon farm. The
growth of oysters were significantly higher in (A) and (B) than in the control
(C). The greatest difference in growth, by a factor of 3, occurred between A
and C. Also the growth of oysters in B was significantly lower than those in
A. The condition index values of oysters showed the same pattern as the
growth, between the 3 stations in September and October. The concentration
of chlorophyll a and b, and particulate organic matter at stations A and B were
significantly higher than at station C. The contribution made by the salmon
farm to the available food in the water may be an important factor in enhancing
the growth of oysters in and around the salmon farm. Introduced pelleted feed
and faecal wastes from the salmon farm into the water, in addition to the
available energy contributed by detritus and bacteria are obvious sources of
energy. This study by Jones and Iwama (1991) provided evidence for the
culture of C. gigas along side a commercial salmon farm and the authors stated
“The elevated feed levels that appear to be closely associated with the intensive
rearing of the Pacific salmon can improve both growth and condition index of
suspended oysters”.

Shpigel et al. (1993) conducted a study in Israel on an integrated farming
system involving the gilthead seabream Spams aurata and the oyster C. gigas.
The fish were reared in 3 PVC lined ponds, each with 100 m2 water spread
area and provided with a daily water exchange of 30 - 50 %. Each pond was

Recent Developments in Oyster Culture

187

stocked with 500 - 770 kg of fish and fed pelleted diet. Oysters of 4-5 months
age (4.8 ± 1 .4 g) were cultured for 60 days at a density of 50 g/1 in plastic mesh
trays held in 600 1 cylindrical tanks. In the oyster culture unit A, water from
a single fish pond was recirculated through this tank. Unit B received effluents
from all the three fish ponds after they have passed through a sedimentation
pond. Oysters in unit C received effluents from all the fish ponds prior to
discharge into the sedimentation pond. The water temperature, salinity, pH ,
ammonia and particulate organic matter values were comparable between the
3 oyster culture units. However, the growth rate of oysters in unit B at 1.56%
/ day was significantly faster than those in unit C at 1.24% / day, and the
oysters in unit C grew significantly faster than those in unit A (0.32% /day).
The condition index (Cl) value of oysters in B at 12.34 was significantly
higher than the value of 9. 14 obtained in unit A and the Cl value in C at 11.21
showed no significant difference between the Cl values of oysters in A and B
units. The authors suggested that the main reasons for the better performance
of the oysters provided with water from the sedimentation pond (unit B) are
due to higher algal diversity, additional nutritious food consisting of attached
benthic diatoms and stable algal concentration.

Remarks

Several studies were conducted using other bivalves such as mussels and
clams as biofilters in treating the fish/shrimp pond effluents. The results
obtained are comparable to those reported for oysters (see Appukuttan and
Kripa, 2001). From India no work seems to have been done using oysters. One
report pertains to the integrated culture of the green mussel Perna viridis and
the shrimp Penaeus monodon carried at Mithapur in Gujarat State
(Subramanyam and Gopalakrishnan, 2000). In a 0.5 ha shrimp pond having
1 m depth, P. monodon seed were stocked at 6 nos/m2 and pelleted shrimp feed
(34-37% protein) was given. After 150 days of culture, shrimp production was
330 kg (average weight 15.9 g ). For mussel culture, 6 racks (authors called
them as rafts but from their figure 2 they are racks) covering 36 m2 area were
constructed in the shrimp pond. Mussel seed of 21.2 mm average length were
transported from Karwar and the seeded ropes were tied horizontally to the
racks. After 150 days of culture the mussels attained 68.5 mm average length
and the production was 306 kg . The growth of the mussels compared
favourably with the results obtained on growth in seafarming by various
authors from India (CMFRI, 1980). Shrimp growth was slow and the authors
attributed this to lower winter temperatures of 21 . 1 to 24.7°C for the major part
of the duration of culture. While this study indicated the feasibility of shrimp
and mussel culture, information on the role of mussels in the biofilteration of
suspended matter is lacking. The available information indicates that oysters
can be successfully used to reduce the concentration of phytoplankton, bacteria
and detritus in the shrimp/fish farm effluent. Instead of direct introduction of

188

Oyster Biology and Culture in India

oysters into shrimp/fish ponds, it is desirable that oysters are introduced into
a separate pond to which the effluent water from shrimp/fish pond is drawn,
after sedimentation. This procedure reduces the concentration of suspended
clay particles, which inhibit filteration by the oysters, resulting in reduced
growth. Further, if the oysters are grown directly in the shrimp/fish pond the
biodeposition (faeces and pseudofaeces) by the oysters adds to the effluent
load in the shrimp/fish pond. Jones et ah (2001) advocated combined culture
of oysters and seaweeds in the same tank. An important aspect to be considered
in these integrated systems of culture is the optimum requirements of various
environmental parameters for the survival and growth of oysters and seaweeds.
The concept of integrated farming systems involving shrimp/fish with bivalves
and seaweeds towards developing sustainable coastal aquaculture has been
successfully tested by several laboratory and field studies. However,
commercialization of integrated farming involving oysters is yet to take off.

In recent years there is growing environmental concern about the adverse
impact of the effluents of shrimp farm wastewater, which is discharged in to
coastal waters. Oysters can be successfully used as biofilters to reduce the
concentration of phytoplankton, bacteria and detritus of shrimp farm effuluent
water, thus improving the health of the environment. It is emphasized that
there is urgency to undertake researches on this aspect in the country.

QUESTIONS

1. What is remote setting? Describe its advantages.

2. Write on triploidy, its induction and advantages in oyster culture.

3. Write an account on oysters as biofilters in aquaculture.

4. Write short notes on: a) Microencapsulated diets b) Cryopreservation of
sperms and D-larvae c) Use of chemicals to enhance spat settlement
d) Probiotics e) Heterosis f) Aneuploidy

Chapter 12

Strategies for Development of

Oyster Culture

IN India, oyster culture is in an early stage of development. Since 1996,
small-scale oyster culture has been taken up by villagers in the estuaries of
Kerala state and the current annual production is between 750-800 tonnes.
Women are participating in oyster culture activities such as preparation of
rens, post-harvert handling and marketing. The Central Marine Fisheries
Research Institute (CMFRI) after having developed oyster culture technology,
is organizing awareness campaigns, setting demonstration farms in
various places, and is providing technology support on a continuous basis for
the benefit of the farmers. Realising the potential of oyster culture for
employment and income generation in the coastal rural areas, Financial
Institutions and Development Agencies are providing finance to oyster farmers.
As a result, oyster culture is spreading fast into new areas with the active
participation of a generation of first time farmers. Based on the information
documented on oyster resources and culture in the country in the preceding
Chapters, the gaps in the knowledge, future research needs, constraints faced
by farmers and the steps to be taken for the development of oyster resources
and culture on a sustainable basis in the Indian context are dealt in this
Chapter.

OYSTER RESOURCES

The taxonomy of the oysters occurring in India needs detailed studies. Among
the commercially important oysters Crassostrea madrasensis is by far the
most important. A few surveys conducted over a period of time in several
water bodies in the states of Andhra Pradesh, Tamil Nadu and Kerala gave
valuable information about the species composition, distribution, population
density, biomass, and size composition of oysters. From other states, the
information available is scanty and there is need to assess the magnitude of
oyster resources in these states. At present there is no system of monitoring the
production of oysters. It is necessary to regularly monitor the production, and
to study the various population parameters of the exploited stocks, at least at
the major production centres so that appropriate management measures can be
taken.

190

Oyster Biology and Culture in India

BIOLOGY

The biology of C.madrasensis has been studied in considerable detail from
several parts of the country. However, an important aspect such as descriptions
of distinctive characters of oyster larvae for identification from plankton is not
studied in this species. Also, except for the reports on the occurrence of the
protozoan parasite Perkinsus marinus and trematode parasites, no detailed
studies on oyster parasites and diseases are made. Oysters are susceptible for
infections by viruses, bacteria, trematodes, and cestodes etc., which cause
oyster mortalities. With oyster culture expanding, information is called for on
the parasites and diseases of oysters and the prevention and control measures.

Both C.gryphoides and Saccostrea cucullata are smaller species with
slower growth rate when compared to C.madrasensis. Very few biological
studies were conducted on the former two species.

NATURAL SEED

In India, at present farmers use natural seed for culture. In the global scenario
also, more than 90% of the seed is sourced from the natural spatfall. In oyster
biology it is well known that while many areas may be suitable for grow out
culture, spat fall in sufficient quantities for commercial operations occurs only
in a few places. For example in Japan, Sendai Bay is known to be most
productive for spat collection. Although several studies have been made in
India on the seed resources from different areas, it is necessary to generate
comprehensive data base about the season and seed availability for commercial
operations. The Ashtamudi Lake has proved to be a very good site for seed
collection. There is intense spat settlement in this area for about three months,
forcing the farmers to scrap the spat that settled later, along with foulers so as
to ensure better oyster growth. As oyster culture grows it is worth while for
the farmers of Ashtamudi Lake area to lay additional spat collectors and sell
the seed to culturists in other areas.

In Thailand, natural seed is scrapped from the cultch and cemented on
ropes at suitable distance for grow out culture. Although labour intensive this
method ensures optimum utilisation of the seed and may be tried at the
Ashtamudi Lake where excessive spat set is wasted.

HATCHERY SEED

The methods followed in India for broodstock conditioning, induced spawning
and larvae / spat rearing have given consistent results. It was reported from
Thailand that fish or shrimp ponds with high phytoplankton production provide
excellent facilities for oyster broodstock conditioning. It is desirable to assess
the suitability of such facilities for broodstock development.

A major problem faced by the hatcheries throughout the world is to
maintain synchronization of the production of live microalgae in sufficient

Strategies for Development of Oyster Culture

191

quantities, depending upon the food requirements of the broodstock , larvae
and spat held in the hatchery. Microalgae, dried as powder or in paste form are
successfully used in many hatcheries as a partial substitute to live microalgae.
Similarly it is reported that addition of Carbon dioxide gas enhances the
microalgae growth, resulting in up to 6.0 million cells / ml against 1.0 - 1.5
million cells by the conventional method. These aspects call for detailed
studies in order to develop appropriate technology to meet these requirements
in the hatcheries.

Considerable research input is also required on aspects such as artificial
diets (microencapsulated diets, yeasts and manipulated yeasts), cryopreservation
of embryos and larvae, and probiotics before they are considered for commercial
use.

Remote setting of oyster larvae has great potential once hatchery seed are
used for commercial operations. The study conducted in the country involving
18 hours transport gave highly encouraging results and there is need to
develop techniques for long duration transport covering 2-3 days.

The neuroactive compounds such as epinephrine, nor-epinephrine, L -
DOPA and GABA induce oyster larvae to settle and metamorphose (without
settlement surface) as cultchless spat and up to 90% success was reported
which is more than double generally obtained in the hatcheries. At present
cultchless spat are not used in oyster culture in India. Nevertheless, in the long
term perspective it is desirable to generate information on this aspect.

NURSERY REARING OF SEED

Spat from commercial hatcheries are reared in nurseries till they reach 20-25
mm size. For this purpose several designs of upwelling systems have been
developed which are either land-based or positioned on rafts or floats in bays
and estuaries. These ‘upwellers’ are usually attached to the hatcheries and
provide greater control over seed rearing, resulting in higher survival. There
is no immediate commercial application of the upwelling systems in
the country since natural seed are presently used but as a part of hatchery
technology upgradation, it is desirable to undertake researches on the upwelling
systems.

GENETICS

Considerable progress was made in oyster genetics in the USA towards
improving their performance in aquaculture. Although not fully put to
commercial use, genetic parameter estimates, selection, inbreeding, heterosis
and heterozygosity have generated valuable information in enhancing the
growth rate, survival and disease resistance in C. gigas and C. virginica. It
is suggested that in India investigations on oyster genetics on the above
aspects should be initiated. The most significant achievement in oyster genetics
is the production of triploids which have several advantages over diploids

192

Oyster Biology and Culture in India

such as steady condition index enabling year round marketability, higher
growth rate resulting in increased meat yield, and in population control.
Triploids are widely used in the commercial culture of C.gigas along the
Pacific coast of USA where hatchery seed form the basis of farming operation.
The oyster farmers in Kerala have no option except to harvest the oysters
before the peak spawning period so as to avoid losses due to poor condition
of the oyster meat due to spawning. Triploid oysters greatly mitigate this
problem and a staggered harvest can be planned depending upon market
demand, provided the various environmental parameters of the culture site
are within the tolerable range of the oysters.

GROW OUT CULTURE

There are several aspects of grow out culture which include species and site
selection, farming technology, monitoring the health of the culture site and the
farmed stock and information on the carrying capacity of the grow out site.
Sound database on the above aspects helps to take appropriate management
measures towards developing oyster farming as a sustainable activity in the
country.

Oyster Species Selection

Among the commercially important oysters in India, C.madrasensis is by far
the most important species. It has wider distribution, eury haline and thrives
well in backwaters and estuaries, amenable to culture, grows fast reaching
market size in 6-8 months grow out culture and is widely marketed. As a
consequence, this species is the basis of commercial aquaculture production of
oysters from the country.

C.gryphoides has restricted distribution along the west coast, thrives well
in estuaries and is a smaller species with slower growth rate. Saccostrea
cucullata is widely distributed, occurring at the mouth of the estuaries and
prefers marine environment; it is also a smaller species with slower growth
rate (Chapters 2&3). Both these species seem to have limited potential as
aquaculture candidates.

Culture Sites

Several studies were conducted in the four southern states, and certain sites
suitable for C. madrasensis culture have been identified (Chapter 7).
Nevertheless there is need to identify more water bodies from these four states
and also from other maritime states from where there is no information
available at present. For this purpose, location testing programs may be
undertaken, using the wild and hatchery raised seed.

There are no extant laws to make available sites suitable for oyster culture
to farmers on lease basis. For this purpose necessary laws should be enacted.

Strategies for Development of Oyster Culture

193

taking into consideration other activities such as traditional fishing, recreation,
navigation and tourism.

Culture Methods

The rack and ren method of oyster culture has proved to be highly suitable in
the estuaries. The technology of rack and tray culture method has also been
developed. There are other methods of oyster culture practiced in many
countries and their suitability under Indian conditions needs to be studied.

In France, on-bottom oyster culture is extensively practiced. It was reported
that cultchless and attached spat of C.madrasensis, set on oyster shells planted
on the bottom in the Kormapallam canal and Karapad creek at Tuticorin
attained 75 mm average length in one year. Both production rate and input cost
by this culture method are known to be low, and more importantly, it is
substrate specific, requiring hard bottom. In suitable areas this method of
culture may be given a trial.

Much of the oyster production from Japan comes from raft and longline
culture and the farms are set up in waters upto 30 m depth from the shore. In
India no studies were conducted in open waters using rafts and longlines for
oyster culture but open sea raft culture of mussels brought to light the
difficulties in maintaining the rafts in position due to rough sea
conditions. Further, C.madrasensis is an estuarine species and the prospects of
developing raft / longline culture of this species in open coastal waters appear
to be bleak.

Public Health

The oysters are known to accumulate pollutants such as pathogenic bacteria
and viruses, toxins produced by algae, and heavy metals, pesticides and
hydrocarbons. Consumption of these oysters by humans causes several diseases
and at times proves fatal. In temperate countries standards for the safe levels
of various pollutants are fixed and the culture sites and the farmed stock are
regularly monitored. If the level of pollutants is high, harvesting of the shell¬
fish is closed. There is urgent need to regularly monitor the sediment and the
quality of water of the culture sites and the farmed oysters for pollutants.
Currently this is one of the weakest links in oyster culture and has a significant
bearing in building public confidence for the expansion of the market. Also
depuration facilities should be developed at suitable areas so as to ensure the
quality of the oyster meat.

Carrying Capacity and Biodeposition

It has long been recognized that large aggregations of shell-fish may have a
significant impact on nutrient and energy recycling in shallow marine
ecosystems (Dame et al., 1980). Carrying capacity denotes the ability of the
ecosystem to support shell-fish production without affecting the growth rates;

194

Oyster Biology and Culture in India

uncontrolled increase in the stocking density eventually results in reduced
growth rate and degradation of the environment. In China, Japan and Thailand
there are reports of oyster culture being carried at high stocking density,
exceeding the carrying capacity of the water bodies (chapter 10). It is time to
undertake studies in the country on the carrying capacity of the culture sites
before the damage is done.

Biodeposition of oysters is another aspect to be considered. Seasonal
cropping pattern followed by Kerala farmers is expected to have reduced
detrimental effects of biodeposition when compared to year round farming in
the same site for several years.

Integrated Farming

In several countries efforts are on to develop integrated farming systems using
shrimp / fish pond effluent water for the production of bivalves and seaweeds.
The bivalves are used to reduce the load of suspended particulate matter and
the seaweeds to bring down the concentration of dissolved nutrients so that the
adverse impact on the environment due to the release of pond effluents is
controlled. Apart from their use in land-based farms, introduction of oysters
into salmon cages in seafarming gave encouraging results. The development
of integrated farming systems using oysters as one of the components is an
important area of research that needs priority attention.

ECONOMICS

The available data on the economics of oyster culture is largely based on the
operation of experimental / demonstration farms of CMFRI and is indicative
of the profitability (Chapter 8). There is need to work out the economics based
on commercial operations, taking into consideration the input costs, production
and market value of the produce which change from time to time.

SOCIAL CONSIDERATIONS

It is increasingly realised in recent times that the availability of mere technology
is not adequate for the sustained development of a sector. It is necessary; rather
it has become imperative that various agencies, more importantly the different
communities interested in the sector are comprehensively involved from the
beginning in the formulation, planning, development and implementation of
the programme. As the oyster culture is essentially carried out in the ecosensitive
coastal areas, vibrant community participation would thus ensure not only
developing an integrated perspective on the management of coastal resources
but also a healthy and all round development of the sector.

TECHNOLOGY TRANSFER

The oyster culture technology was developed in the country in 1970’s and it
took about two decades before the commercial farms were set up. As a result

Strategies for Development of Oyster Culture

195

of sustained efforts by the scientists working at the CMFRI, oyster culture is
spreading fast in Kerala (Chapter 9). The continuous interaction of the scientists
with farmers and linking them with organizations such as the Brackishwater
Fish Farmers Development Agency, which is providing finance, augurs well
for the growth of oyster culture. Apart from expanding oyster culture in Kerala
estuaries, there is wide scope to transfer the farming technology to the end
users in other maritime states.

Unlike shrimps, oysters are not traditionally cultured in India. Lack of
awareness about the prospects and economic benefits of oyster culture and
non - availability of trained personnel with adequate knowledge in the culture
system greatly hamper the wider propagation of oyster culture at present. It is
therefore, essential to organise and implement need-based training programmes
to meet the personnel requirement of the sector. The Trainers Training Centre
of the CMFRI is actively working on these lines.

MARKET

Some coastal communities in states such as Kerala, Karnataka, Goa and
Maharashtra and also people in a few metropolitan cities conventionally eat
oysters. In the rest of the country, particularly in the interior parts, oyster
consumption is practically non-existent. Against this domestic scenario, oysters
are among the luxury seafoods in temperate countries such as Canada, USA
and in Europe. The lack of demand is a matter of concern. There is need to
widen the market base, particularly into the interior areas, with vigorous
extension drive by popularizing the oyster products and creating awareness
about the nutritional value. As a result of the efforts at the Central Institute of
Fisheries Technology and the Integrated Fisheries Project (IFP) several oyster
products have been developed. The IFP has ventured into marketing the oyster
products and the reports indicate considerable demand for canned oysters in
the north eastern states and metropolitan cities. As per the figures released by
the Marine Products Development Authority, about 700 tonnes of oyster shell
powder valued at Rs.21 lakhs was exported from the country in 1999 and
oyster meat does not figure in the seafood exports.

Quality assurance is a prime factor for market promotion. To achieve this
adequate care has to be taken beginning with the grow out culture till the
product reaches the consumer. In essence the single most import factor that
calls for immediate attention is the development of market for oyster and
oyster products.

QUESTIONS

1 . Describe the important gaps in knowledge and the thrust areas for R&D

towards developing sustainable oyster farming in the country.

References

Ablan, G.L. 1955. Lattice method of oyster culture. Philippine Journal of Science, 2:
197-201.

Abraham, T.J., S.Balasundari, S.A. Shanmugam and P.Jeyachandran. 1998. Bacterial
depuration of grossly contaminated edible oyster, Crassostrea madrasensis
(Preston). Journal of Marine Biology Association. India, 40 (1&2): 181-184.

Ahmed, M. 1975. Speciation in living oysters. Advances in Marine Biology ., 13:357-
397.

Alagarswami, K. and K.A. Narasimham. 1973. Clam, cockle and oyster resources of
the seas around India. Pages 648-658 in Proceedings of the Symposium. Living
Resources of the Seas around India. Central Marine Fisheries Research Institute,
Cochin.

Alagarswami, K. and M.M. Meiyappan. 1989. Prospects and problems of management
and development of the marine molluscan resources (other than cephalopods) in
India. Bulletin of Central Marine Fisheries Research Institute., 44 ( 1 ): 250-26 1 .

Alderman, D.J. and E.B.G. Jones. 1967. Shell disease of Ostrea edulis L. Nature
(London) 216: 797-798.

Alderman, D.J. 1980. Shellfish disease problems- Past, present and future. Proceeding
of Annual Conference. Shellfish. Assoc., Great Britain, 11: 30-40

Ali, R.M. 1970. The influence of suspension density and temperature on the filtration
rate of Hiatelia arctica. Marine Biology., 6. 291.

Allen, S.K., Jr. 1983. Flow cytometry: assaying experimental polyploid fish and
shellfish. Aquaculture, 33: 317-328.

Allen, S.K., Jr. 1987. Gametogenesis in three species of triploid shellfish Mya arenaria,
Crassostrea gigas and Crassostrea virginica. Pages 207-271 in Proceedings.
World Symposium on Selection, Hybridization and Genetic Engineering in
Aquaculture , Volume II, Heenemann, Berlin.

Allen, S.K., Jr. 1988. Triploid oysters ensure year-round supply. Oceanus, 31: 58-63.

Andrews, J.D. 1964. Oyster mortality studies in Virginia. IV.MSX in James River
public seed beds. Proceeding of National Shellfish Association., 53:65-84.

Andrews, J.D. 1983. Minchinia nelsoni (MSX) infections in the James River seed-
oyster area and their expulsion in spring. Est. Coast. Shelf Sci., 16:255-269.

Angell, C.L. 1986. The biology and culture of tropical oysters. International Centre
For Living Aquatic Resources Management, Studies and Reviews 13: Manila,
Philippines. 42pp.

Annadale, N. and S. Kemp. 1916. Fauna of Chilka Lake, Mollusca:Gastropoda and
Lamellibranchiata. Memoirs of Indian Museum, 5: 329-366.

Appukuttan, K.K., V. Kripa, T.S. Velayudhan, K.S. Mohamed, A.C.C. Victor, P.S.
Kuriakose, P. Laxmilatha and P. Muthiah. 2000. Bivalve Mariculture in India -
A success story in Coastal Ecosystem Development (V.N. Pillai ed.) published
by Asia Pacific Association of Agricultural Research Institutions, F.A.O.
(APAARI Publication: 2000/1). 56 pp.

References

197

Appukuttan, K.K. and V. Kripa. 2001. Integration of shrimp aquaculture with molluscan
culture. Pages 60-73 in Proceedings. International Workshop on Aquaculture
and Environment, The Centre for Integrated Management of Coastal Zones,
Cochin University of Science and Technology.

AQUACOP, 1977. Elevage larvariae et production de naissain de Crassostrea gigas
en milieu tropical. Acetes de colloques du CNEXO, 4:331-346.

Arakawa, K.Y. 1990. Commercially important species of oysters in the world. Mar.
Behav. Physiol., 17:1-3.

Avault, J.W. 1998. Predators and pests of Molluscs; oysters, clams and mussels.
Aquaculture Magazine , Jan/Feb: 56-61.

Awati, P.S. and H.S.Rai 1931. Ostrea cucullata (the Bombay oyster). Indian Zoological.
Memoir., 3:107 pp.

Bahr, L.M. 1976. Energetic aspects of the intertidal oyster reef community at Sape lo
Island, Georgia (USA). Ecology , 57: 121-131.

Bahr, L.M. and W.P. Lanier. 1981 . The ecology of intertidal oyster reefs of the South
Atlantic coast: A community profile. United States Fish and Wildlife Service.
Office of Biological Services, Washington D.C. FWS / OBS - 81/15.
Baldwin, R.B., W. Mook, N.H. Hadley, R.J. Rhodes and R.M. Devoc, 1995.
Construction and operations manual for a tidal-powered upwelling nursery
system. South Carolina Sea Grant Consortium, Marine Extension. Program
Publication. April 1995, Charleston S C. 44 pp.

Balouet, G., M. Poder, and A. Cahour. 1983. Haemocytic parasitosis: morphology and
pathology of lesions in the French flat oyster, Ostrea edulis L. Aquaculture,
34:1-14.

Barber, B.J., S.E. Ford and H.H. Haskin. 1988. Effects of the parasite MSX
(Haplosporidium nelsoni) on oyster (Crassostrea virginica ) energy metabolism.
II. Tissue biochemical composition. Compendium of Biochemical Physiology,
91A: 603-608.

Bardach J.E., J.H.Ryther and W.O. Me Lamey. 1972. Aquaculture, farming and
husbandry of fresh water and marine organisms. Wiley Interscience, New York.

868pp

Baughman, J.L. 1947. An Annotated Bibliography of Oysters, with Pertinent Material
on Mussels and Other Shellfish and an Appendix on Pollution. Texas A&M Res
Found., Agr & Mech Coll.Texas. College Station, Texas. 794 pp.

Bayes, J.C. 1981. Forced upwelling nurseries for oysters and clams using impounded
water systems. Pages 73-83 In: C. Claus, N. Depallus and E. Jaspers (Eds.),
Nursery culturing of bivalve mollusks. Proceedings of the International Workshop
on nursery culturing of bivalve mollusks, European Mariculture Society, Special
Publication 7, Ghent, Belgium.

Beattio, J.H., Me Millain, D and Wiegardt, L. 1982. The Washington State oyster
industry. A brief overview. In Chew, K.K. (Ed.), Proceeding of North American.
Oyster Workshop 1981, Washington: 28-39.

Beaumont, A.R. and J.E. Fairbrother, 1991. Ploidy manipulation in molluscan shellfish:

A review. Journal of Shellfish Research. Research, 10: 1-18.

Bell, A.E. 1982. Selection for heterosis results with laboratory and domestic animals.
Proceedings of the 2nd World Congress on Genetics applied to livestock
production, 6: 206-207.

198

Oyster Biology and Culture in India

Beninger, P.G., M. Le Pennec and A. Donval. 1991. Mode of particle ingestion in five
species of suspension-feeding bivalve molluscs. Marine Biology ., 108: 255-261 .

Bernard, F.R. 1974. Particle sorting and labial palp function in the Pacific Oyster
Crassostrea gigas (Thunberg). Biological Bulletin., 146:1-10.

Bisker, R. and M. Castagna, 1987. Predation on single spat oysters Crassostrea
virginica (Gmelin) by blue crabs Callinectes sapidus Rathbun and mud crabs
Panopeus herbstii Milne - Edwards. Journal of Shellfish Research., 6: 37-40.

Blanco, G.J, 1956. The stake (patusok) method of oyster farming in the Dagatdagaton
Lagoon, Rizal Province. Philippine Journal of Fisheries, 4: 21-30.

Bower, S.M., S.E. McGladdery and I.M. Price. 1994. Synopsis of infectious diseases
and parasites of commercially exploited shellfish. Annual Review of Fish
Diseases, 4: 1-200.

Braumbaugh, R.D., L. Sorabella, C. Oliveras, W.J. Goldsborough, and Wesson. 1998.
Making a case for community-based restoration initiatives: an example from
Hampton Roads Virginia. Journal of Shellfish Research., 17(4). (Abstract ).

Breish, L.L and V.S. Kennedy. 1980. A Selected bibliography of Worldwide Oyster
Literature. Maryland, College Park, Publ. No.UM-SG-TS-80-11. 309 pp.

Bricelj, V.M., S.E. Ford, F.J. Borrero, F.O. Perkins, G., R.E. Hillman, R.A. Elston and
J. Chang, 1992. Unexplained mortalities of hatchery-reared, juvenile oysters,
Crassostrea virginica (Gmelin). Journal of Shellfish Research., 11: 331-347.

Brock, V., V.S. Kennedy and A. Brock. 1986. Temperature dependency of carbohydrase
activity in the hepatopancreas of thirteen estuarine and coastal bivalve species
from North American east coast. Journal of Experimental Marine Biology and
Ecology., 103:87-101.

Bromanonda, P. 1978. Study on some biological aspects and culture of oyster. Thailand
Fisheries Gazette, 31: 202-228.

Brooks, W.K. 1880. The development of the American oyster. Stud. Biol. Lab. Johns
Hopkins University, 4: 1-104.

Brooks, W. K. 1905. The Oyster. A popular summary of a scientific study. Second ed.
The Johns Hopkins University Press, Baltimore. 225 pp.

Brown, C. and E. Losee. 1978. Observations on natural and induced epizootics of
Vibriosis in Crassostrea virginica larvae. Journal of Invertebrate Pathology.,
31: 41-47.

Brown, J.R. and Hartwick. E.B. 1988. Influences of temperature, salinity and available
food on suspended Culture of the Pacific oyster Crassostrea gigas. Aquaculture
and Fisheries Management, 19: 107-124.

Burnell, G.M. 1994. New methods for the monitoring and manipulation of bivalve
molluscs. In: Kestemont, P, J. Muir, F. Sevila and P. Williot (Eds.). Measures
for success. CEMAGREF-Edition : 149-153.

Buroker, N.E., P. Chanley, H.J. Cranfield and P. Dinamani. 1983. Systematic status of
two oyster populations of the genus Tiostrea from New Zealand and Chile.
Marine Biology. 54: 157-169.

Bushek, D., S.K. Allen, K.A. Alcox, R. Gustafson and S.E. Ford. 1994. Dose response
of the eastern oyster, Crassostrea virginica, to cultured cells of Perkinsus
marinus, the agent of Dermo disease. Journal of Shellfish Research., 13: 313.

Butler, PA. 1949. Gametogenesis in the oyster under conditions of depressed salinity.
Biological Bulletin. 96:263-269.

References

199

Butler, P.A. 1954. The southern oyster drill. Proceeding of Natural Shellfish Association.
(1953): 67-75.

Cadoret, J.P. 1992. Electricfield-induction of polyploidy in mollusc embryos.
Aquaculture, 106(2): 127-139.

Carlton, J.T. and R. Mann. 1996. Transfers and worldwide introductions. Pages 69 1 -
702 In V.S. Kennedy, R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster
Crassostrea virginica , published by the Maryland Sea Grant College, University
of Maryland System, College Park.

Calvo, G.W. and E.M. Burreson, 1994. In vitro and in vivo effects of eight
chemotherapeutants on oyster parasite Perkinsus marinus (Mackin, Owen and
Collier). Journal of Shellfish Research., 13: 101-107.

Canzonier, W.J. 1988. Public health component of shellfish production and marketing.

Journal of Shellfish Research., 7(2): 261-266.

Carreon, J.A. 1969. The malacology of Phillippine oysters of the genus Crassostrea
and a review of their shell characters. Proceeding of Natural Shellfish. Association.
59:104-115.

Carriker, M.R, 1961a. Comparative functional morphology of boring mechanisms in
gastropods. American Zoology., 1: 263-266.

Carriker, M.R. 1961b. Interrelation of functional morphology, behaviour and
autoecology in early stages of the bivalve Mercenaria mercenaria. Journal
Elisha Mitchell Scientific Society., 77 (2): 168-241.

Carriker, M.R. 1976. The crucial role of systematics in assessing pollution effects on
the biological utilization of estuaries. Pages 487-506 in Estuarine pollution
control and assessment, Proceeding of the Conference., vol. 1, 2, U.S.
Environmental Protection Agency, Officer of Water planning and standards,
U.S. Govt. Office.

Carriker, M.R. 1996. The shell and ligament. Pages 75-159 in V.S. Kennedy, R.I.E.
Newell and A.F. Eble (Eds.), The Eastern oyster, Crassostrea virginica. Sea
Grant College Park, Maryland.

Carriker, M.R. and P.M. Gaffney. 1996. A catalogue of selected species of living
oysters (Ostreacea) of the world. Pages 1-15 in V.S. Kennedy, R.I.E. Newell and
A.F. Eble (Eds.), The Eastern oyster Crassostrea virginica. University of
Maryland System, College Park.

Carriker, M.R., C.P. Swann and J.W. Ewart. 1982. An exploratory study with the
proton microprobe of the ontogenetic distribution of sixteen elements in the
shell of living oysters ( Crassostrea virginica ). Marine Biology. 69:235-246.

Carriker, M.R., C.P. Swann, R.S. Prezant and C.I. Counts. 1991. Chemical elements
in the aragonite and calcitic microstructural groups of shells of oyster, Crassostrea
virginica -a proton probe study. Marine Biology., 109: 287 -297.

Castagna, M., M.C. Gibbons and K. Kurkowski. 1996. Culture: Application. Pages
679-690 in V.S. Kennedy, R.I.E. Newell and A.F. Eble (Eds.), The Eastern
Oyster Crassostrea virginica. Maryland Sea Grant College, University of
Maryland System, College Park.

Chaiton, J.A. and S.K. Allen. Jr. 1985. Early detection of triploidy in the larvae of
Pacific oysters, Crassostrea gigas , by flow cytometry. Aquaculture, 48: 35-43.

Chan, K.W., R.Y.H. Cheung, S.F. Leung and M.H. Wong. 1999. Depuration of metals

200

Oyster Biology and Culture in India

from soft tissues of oysters ( Crassostrea gigas ) transplanted from a contaminated
site to clean sites. Environmental pollution, 105: 299-310.

Chao, N.H., T.T. Lin, Y.J. Chen, H.W. Hsu and I.C. Liao. 1997. Cryopreservation of
late embryos and early larvae in the oyster and hard clam. Aquaculture , 155: 3 1 -
44.

Chellam, A., S. Dharmaraj, T.S. Velayudhan and P. Muthiah. 1988. Experimental
molluscan seed transport. Mar. Fish. Inf or. Serv. T & E Ser.,19 : 26 - 28.

Chen, S.P. 1992. Traditional oyster products. INFOEISH International, 5/92: 27-32.

Cheng, T.C. 1996. Haemocytes: forms and functions. Pages 299-320 in V.S. Kennedy,
R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster Crassostrea virginica ,
published by the Maryland Sea Grant College, University of Maryland System,
College Park.

Chew, K.K. 1991. Hatchery development and remote setting of the Pacific oyster
larvae. Aquaculture Magazine., 17 (4): 72-75.

Chew, K.K. 1994. Tetraploid Pacific oysters offer promise to future production of
triploids. Aquaculture Magazine., 20: 69-74.

Chew, K.K.2001. Worldwide statistics for oysters and clams. Aquaculture Magazine.,
May/June: 72-76.

Chew, K.K., A.K. Sparks and S.C. Katkansky. 1964. First record of Mytilicola
orientalis Mori in the California mussel Mytilus californianus. J. Fish. Res.
Board Can., 21:205-207.

Chhaya, N.D., A.Y. Desai and Y.B. Raval. 1993. Research and development work
carried out on edible oysters in Gujarat. Mar. Fish. Inf or. Serv., T&E Ser.,
No. 125: 7-9.

Chichester, C.O. and H.D. Graham. 1973. Microbial safety of Fishery products.
Academic press, New York. 344 pp.

Child, A.R. and H.P. Watkins. 1994. A simple method to identify triploid molluscan
bivalves by measurement of cell nucleus diameter. Aquaculture, 25: 199-204.

Ching, H.L. 1972. A redescription of Gymnophalloides tokiensis Fujita, 1925
(Trematode: Gymnophallidae). Canadian Journal of Zoology., 50:1299-1302.

Chu, F.L.E., K.L. Webb, D.A. Hepworth and B.B. Casey. 1987. Metamorphosis of
larvae of Crassostrea virginica fed microencapsulated diets. Aquaculture, 64:
185-197.

Chu, F.L.E. and Greaves. 1991. Metabolism of palmitic, linoleic and linolenic acids in
adult oysters, Crassostrea virginica. Marine Biology., 110: 229-236.

Churchill, E.P. 1920. The oyster and the oyster industry of Atlantic and Gulf coasts.
US Bureau of Fisheries, Report of the Commissioner of fisheries for the fiscal
year 1919. Appendix 8 (Document 890). 5 1 pp

Clarke, T.M., S.L. Sanders and G.F. Newkirk. 1991. Spatfall monitoring and spat
collection of oysters in Jamaica. Pages 87-97 in: GF.Newkirk and B.A.Field
(Eds.), Oyster culture in the Carribean. Mollusc culture network, Dalhousie
University, Halifex, Nova Scotia, Canada.

Cliver, D.O. 1997. Virus transmission via feed. World Health-Statistics. Q., 50 (1-2):
90-101.

CMFRI, 1979. Coastal Aquaculture. Spl. Pub., 6: 96 pp.

References

201

CMFRI, 1980. Coastal Aquaculture: Mussel farming: Progress and prospects. Bulletin
of Central Marine Fisheries Research Institute., 29: 56 pp.

CMFRI, 1987. Oyster culture-Status and Prospects. Bulletin of Central Marine Fisheries
Research Institute., 38:78 pp.

CMFRI, 2001 . Central Marine Fisheries Research Institute Annual Report 2000-2001.
Cochin, India., 163 pp.

Coan, E.V., PH. Scott and F.R. Bernard. 1 995. Bivalve seashells of western north America.
Marine bivalve molluscs from Arctic Alaska to Baja California. Santa Barbara
Museum of Natural History, Santa Barbara, California.

Coen, L., E. Wenner, D. Knott, B. Stemder, N. Hadley, M. Bobo, D. Richardson, M.
Thompson, and R. Giotta. 1997. Intertidal oyster reef habitat assessment and
restoration: evaluating habitat use, development and function. Journal of Shellfish
Research. 16:262.

Coen, L.D., Luckenbach, M.W. and O.L. Breitburg. 1999. The role of oyster reefs as
essential fish habitat: a review of current knowledge and new perspectives.
American Fisheries Society Symposium. South Carolina Sea Grant Programme.
22: 438-454.

Cole, H.A. and D.A. Hancock. 1956. Progress in oyster research in Britain 1949-1954,
with special reference to the control of pests and diseases. Rapp. RV. Reun.,
Cons. Int. Explor. Mer., 140:24-29.

Collwell, R.R. and A.K. Sparks. 1967. Properties of Pseudomonas enalia, a marine
bacterium pathogenic for the invertebrate Crassostrea gigas (Thunberg). Applied
Microbiology., 15:980-986.

Comps, M. 1978. Evoultion des recherches et etudes recentes en patologie des huitres.
Oceanol. Acta., 1: 255-262.

Comps, M., and J.L. Duthoit. 1976. Infection virale associee a la maladie des branchies
de Phuitre portugaise Crassostrea angulata Lmk. C.R. Hebd. Seances Acad.
Sci., Ser. D., 283: 1595-1596.

Coon, S.L., D.B. Bonar and R.M. Weiner, 1985. Induction of settlement and
metamorphosis of the Pacific oyster, Crassostrea gigas (Thunberg) by L-Dopa
and catecholamines. Journal of Experimental Marine Biology and Ecology., 94:
211-221.

Coon, S.L., D.B. Bonar and R.M. Weiner. 1986. Chemical production of cultchless
oyster spat using epinephrine and nor-epinephrine. Aquaculture, 58: 255-262.
Coon, S.L., W.K. Fitt, D.B. Bonar, 1990. Competence and delay of metamorphosis in
the Pacific oyster Crassostrea gigas. Marine Biology., 106: 379-387.
Coughlan, J. 1969.The estimation of filtering rate from the clearance suspensions.
Marine Biology., 2: 356-358.

Coutteau, P. and P. Sorgeloos. 1993. Substitute diets for live algae in the intensive
rearing of bivalve molluscs-a state of the art report. World Aquaculture, 24 (2):
45-52.

Craig, A., E.N. Powell, R.R. Ray and J.M. Brooks. 1989. Distribution of Perkinsus
marinus in Gulf coast oyster populations. Estuaries, 12: 82-91.

Cranfield, H.J. 1975. The ultra structure and histochemistry of the larval cement of
Ostrea edulis L. Journal of Marine Biological Association. U.K., 55:497-503.

202

Oyster Biology and Culture in India

Crenshaw, M.A.1990. Biomineralization mechanisms. Pages 1-9 in J.G. Carter (Eds.),
Skeletal Biominerilization: Patterns, Processes and Evolutionary Trends ,
Vol.I.Van Nostrand Reinhold, New York.

Crosby, N.D. and R.G. Reid. 1971. Relationships between food, physiology and
cellulose digestion in Bivalvia. Canadian Journal of Zoology., 49:617-622.

Crosby, M.P and L.D. Gale. 1990. A review and evaluation of bivalve condition index
methodologies with a suggested standard method. Journal of Shellfish Research.,
9(1): 233-237.

Dame, R., R. Zingmark and D. Nelson. 1980. Filter feeding coupling between the
estuarine water column and benthic systems. In: V.S. Kennedy (Ed.), Estuarine
Perspectives, Academic Press, New York: 521-526.

Dame, R.F. 1996. Ecology of Marine Bivalves. CRC Press, Boca Raton, Florida.

Das, S.K. 1993. Prospects of oyster fisheries along Bahuda estuary of Orissa. Fishing
Chimes, May 13(2): 17-18.

Davis, P.J. 1989. Growth rate of sibling diploid and triploid oysters, Crassostrea gigas.
Journal of Shellfish Research., 8: 3 19( Abstract).

De Alteris, J. T. 1988. The geometric development of Wreck shoal, a subtidal oyster
reef of the James river, Virginia. Estuaries, ll(4):240-249.

Desai, K.M. and D. Nimavat. 1983. Neuroendocrine control of reproduction in some
edible oysters. Proceeding of Symposium. Coastal Aquaculture, Pt. 2:500-504.

Desrosiers, R.R., A. Gerard, J.M. Peignon, Y. Naciri, L. Dufresne, J. Morasse, C.
Ledu, P. Phelipot, P. Guerrier and F. Dube. 1993. A novel method to produce
triploids in bivalve molluscs by the use of 6-dimethylaminopurine. Journal of
Experimental Marine Biology and Ecology., 170: 29-43.

Dillon, R.T. and J.J. Manzi. 1987. Hard clam Mercenaria mercenaria broodstocks:
genetic drifts and loss of rare alleles without reduction in heterozygosity.
Aquaculture. 60: 99-105.

Dimitroff, V.T. 1926. Spirochaetes in Baltimore Market oysters. Journal of Bacteriology.,
12:65-135.

Dinamani, P. and D.B. Gordan. 1974. On the habits and nature of association of the
copepod Pseudomyicola spinosus with the rock oyster Crassostrea glomerata in
New Zealand. Journal of Invertebrate Pathology., 24:305-310.

Dinamani, P., PM. Hine and J.B. Jones. 1987. Occurrence and characteristics of the
haemocyte parasite Bonamia sp. in the New Zealand dredge oyster Tiostrea
lutaria. Dis. Aquat. Org., 3:37-44.

Dittman, D.E. 1993. The quantitative effects of Perkinsus marinus on reproduction
and condition in the eastern oyster, Crassostrea virginica. Proceedings of
National Shellfish Association. 65: 1. (Abstract).

Dixon, D.R. 1982. A new ploidy in mussel embryos (Mytilus edulis L) originating
from a polluted lake. Marine Biology. Lett. 3: 155-161.

Donaldson, J. 1991. Rotifer and microalgal culture systems, Pages 229-236 in W.
Fulks and K.F. Main (Eds.). Proceedings ofUS-Asia Workshop, Honolulu. The
Oceanic Institute, Hawaii.

Douillet, PA. and C.J. Fangdon. 1994. Use of probiotic for the culture of larvae of the
Pacific oyster ( Crassostrea gigas Thunberg). Aquaculture, 119: 25-40.

References

203

Downing, S.L. 1989. Estimating polyploid percentages using oyster larvae: a valuable
hatchery management research tool. Journal of Shellfish Research., 8(1): 320
(Abstract).

Dunathan, J.P., R.M. Ingle and W.K. Havens. 1969. Effects of artificial foods upon
oyster fattening with potential commercial applications. Florida Research
Laboratory Technical Services, 58: 1-38.

Dupuy, J.L., N.J.Windsor and C.E. Sutton. 1977. Manual on design and operation of
an oyster seed hatchery for the American oyster, Crassostrea virginica.
International Marine Science Special Report, 142: 1-104.

Durve, V.S. 1964. On the percentage edibility and the index of condition of the oyster
Crassostrea gryphoides (Schlotheim). Journal of Marine Biological Association.
India, 6:128-134.

Durve, V.S. 1965. On the seasonal gonadal changes and spawning in the adult oyster,
Crassostrea gryphoides (Schlotheim). Journal of Marine Biological Association.
India, 7: 328-344.

Durve, V.S. 1968. On the nomenclature of two Indian backwater oysters. Journal of
Marine Biological Association. India, 9: 173-178.

Durve, V.S. 1986. On the ancestory and distribution pathways of three species of
Indian oysters. Indian Journal of Marine Sciences.,. 15: 56-58.

Durve, V.S. and D.V. Bal. 1960. Shell disease in Crassostrea gryphoides (Schlotheim).
Current Science., 20: 489-490.

Durve, V.S. and D.V. Bal. 1962. Preliminary observations on the growth of spat of the
oysters Crassostrea gryphoides (Schlotheim). Journal of Marine Biological
Association. India., 4(2): 206-213.

Eble, A.F. 1996. The Circulatory system. Pages 271-296 in: V.S. Kennedy, R.I.E.
Newell and A.F. Eble (Eds.), The Eastern oyster Crassostrea virginica, published
by the Maryland Sea Grant College, University of Maryland System, College
Park.

Eble, A. F. and R. Scro. 1996. General Anatomy. Pages 19-74 in: V.S. Kennedy, R.I.E.
Newell and A.F. Eble (Eds.), The Eastern oyster Crassostrea virginica, published
by the Maryland Sea Grant College, University of Maryland System, College
Park.

Elner, R.W. and R.E. Lavoie. 1983. Predation on American Oysters ( Crassostrea
virginica (Gmelin) by American lobsters ( Homarus americanus Milne Edwards),
rock crabs ( Cancer irroratus Say), and mud crabs (Neopanope sazi (Smith)).
Journal of Shellfish Research., 3: 129-134.

Elston, R.A. 1979. Virus like particles associated with lesions in larval Pacific oysters
(Crassostrea gigas). Journal of Invertebrate Pathology., 33:71-74.

Elston, R.A. 1980. Ultrastructural aspects of a serious disease of hatchery reared larval
Pacific oysters, Crassostrea gigas. Proceedings of National Shellfish Association.,
70:122.

Elston, R.A. 1984. Prevention and management of infectious disease in intensive
mollusc husbandry. Journal of World Mariculture Society., 15: 284-300.

Elston, R.A. 1990. Mollusc Diseases: Guide for the shellfish farmer. Washington Sea
Grant Publication, University of Washington Press, Seattle. 73 pp.

Elston, R.A. 1993. Infectious diseases of the Pacific oyster, Crassostrea gigas. Annual
Review of Fish Diseases, 2: 259-276.

204

Oyster Biology and Culture in India

Elston, R.A., and M.T. Wilkinson. 1985. Pathology, management and diagonosis of
oyster velar virus disease (OVVD). Aquaculture, 48:189-210.

Enriques, R., G.G. Frosner, V. Hochstein-Mintzel, S. Riedeman and G. Reinhardt.
1992. Accumulation and persistence of Hepatites A virus in mussels. Journal of
Medical Virology, 37: 174-179.

Esterson,D.C.V and D.Kandasami. 1988. Biochemical changes in the oyster Crassostrea
madrasensis (Preston) with maturation. Bulletin of Central Marine Fisheries
Research Institute. 42 (1): 203-204

Eudeline, B., S.K. Allen., Jr. and X. Guo. 2000. Optimisation of tetraploid induction
in Pacific oyster, Crassostrea gigas, using first polar body as a natural indicator.
Aquaculture, 187: 73-84.

Fairfull, R.W. 1990. Heterosis. In: Poultry breeding and genetics, 913-933,
R.D.Crawford (Ed), Elsevier Science Publishers, Amsterdam.

Falconer, D.S. 1981. Introduction to quantitative genetics, 2nd ed. Longman, London
340 pp.

FAO 1983. Compilation of legal limits for hazardous substances in fish and fishery
products. FAO Fisheries Circular No. 764, FAO, Rome.

FAO 1998. Seaweeds, Corals, bivalves and Gastropods. Pages 224-233 in the Living
Marine Resources of the Western Central Pacific Volume 1 .

FAO 2003a. Capture production 1950-2003 Vol. 96/1.

FAO 2003 b. Fishery statistics. Aquaculture production: quantities 1950-2003. Vol 96/

Farley, C.A. 1968. Minchinia nelsoni (Haplosporida, Haplospordiidae) disease syndrome
in the American oyster, Crassostrea virginica. Journal of Protozoology. 15:
585-599.

Farley, C.A. 1973. Virus diseases of oysters. Wildl. Dis. Conf. 19 pp.

Farley, C.A. 1978. Viruses and virus like lesions in marine molluscs. Marine Fisheries
Review. 40: 1 8-20.

Farley, C.A., W.G. Banfield, G., Jr, Kasnic and W.S. Foster. 1972. Oyster herpes-type
virus. Science, 178:759-760.

Farley, C.A. and E.J. Lewis. 1993. Juvenile oyster mortality studies-1992:
histopathology, pathology, epizootiology. Journal of Shellfish Research., 12:
107. (Abstract).

Fingerman,M and L.D. Fairbanks 1955. Some factors affecting fluid loss in Southern
oysters. Comm. Fish. Rev. 18 (1) : 10-11

Fingerman,M and L.D. Fairbanks 1957. Heat, death and associated weight loss of the
oyster Crassostrea virginica. Tulane studies in Zoology and Botany 5 : 55-68.

Fisher, W.S. 1988. Disease Processes in Marine Bivalve Molluscs. American Fisheries
Society Special Publication. 18. Bethesda, Maryland. 315 pp.

Fitt, W.K., S.L. Coon, M. Walch, R.M. Weiner, R.R. Colwell and D.B. Bonar. 1990.
Settlement behavior and metamorphosis of oyster larvae ( Crassostrea gigas ) in
response to bacterial supernatants. Marine Biology., 106: 389-394.

Foltz, D.W., G.F. Newkirk and E. Zouros. 1983. Genetics of growth rate in the
American oyster: absence of interactions among enzyme loci. Aquaculture, 33:
157-165.

References

205

Fong, D., R. Rodriquez, K. Koo, J. Sun, M.L. Sogin, D. Bushek, T.D.J. Littlewood and
S.E. Ford. 1993. Small sub unit ribosomal RNA gene sequence of the oyster
parasite Perkinsus marinus. Mol. Mar. Biol. Biotechnol., 62: 139-142.

Ford, S.E. 1994. Unexplained mortalities of hatchery reared oysters, Crassostrea
virginica, in the Northeast: A follow up study. Rugers University. (Final Technical
Report to the Northeastern Regional Aquaculture Center. Copies available from
S. Ford, Rugers University, Haksin Shellfish Research Laboratory, Port Norris,
NJ, USA). 27pp.

Ford, S.E. and H.H. Haskin. 1982. History and epizootiology of Haplosporidium
nelsoni (MSX), an oyster pathogen, in Delaware Bay, 1957-1980. Journal of
Invertebrate Pathology., 40 : 118-141.

Ford, S.E and M.R.Tripp 1996. Diseases and defence mechanisms. In V.S. Kennedy,
R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster Crassostrea virginica.
Sea Grant College Park, Maryland, pp. 581-642.

Ford, S.E., R.N. Wargo and L.M. Ragore. 1988. Metabolic condition and infection
levels preceding death in oysters exposed to Haplosporidium nelsoni (MSX)
with an hypothesis about cause of death. In Abstracts of 3rd International
Colloquium on Pathology in Marine Aquaculture , Gloucester Point, Virginia,
pp. 41-42.

Friedman, C.S. and R.P. Hedrick. 1991. Pacific oyster nocardiosis: Isolation of the
bacterium and induction of laboratory infection. Journal of Invertebrate
Pathology., 57: 109-120.

Fuller, R. 1989. Probiotics in man and animals. J. Appl. Bacteriol., 66: 365-378.

Gaffney, P.M. 1996. Biochemical and population genetics. Pages 423-441 in V.S.
Kennedy, R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster Crassostrea
virginica , Maryland Sea Grant College Publications.

Gaffney, P.M. and S.K. Allen., Jr. 1993. Hybridization among Crassostrea species: a
review. Aquaculture, 116: 1-13.

Galtsoff, PS. 1964. The American oyster Crassostrea virginica Gmelin. U.S. Fish and
Wildlife Serv. Fish. Bull., 64: 430-441.

Gatesoupe, F.J. 1999. The use of probiotics in aquaculture. Aquaculture, 180: 147-
165.

Gerard, A., Y. Naciri, J.M. Peignon, C. Ledu and P. Phelipot. 1994a. Optimisation of
triploid induction by the use of 6-DMAP for the oyster Crassostrea gigas
(Thunberg). Aquaculture and Fisheries Management , 25: 709-719.

Gerard, A., Y. Naciri, J.M. Peignon, C. Ledu, P. Phelipot, C. Noiret, I. Peudenier and
H. Grizel. 1994b. Image analysis: a new method for estimating the ploidy in
commercial bivalves. Aquaculture and Fisheries Management , 25: 697-708.

Ghode, G.S. and V. Kripa. 2001. Polydora infestation on Crassostrea madrasensis: a
study on the infestation rate and eradication methods. Journal of Marine
Biological Association. India , 43 (1&2): 110- 120.

Gibbons, M.C. 1988. Development of nursery techniques for remote set larvae of
Crassostrea virginica in Virginia. Journal of Shellfish Research, 7(1): 160.

Gibbons, M.C and M. Castagna. 1984. Serotonin as an inducer of spawning in six
bivalve species. Aquaculture, 40: 189-191.

206

Oyster Biology and Culture in India

Gibson, L.F., J. Woodworth and A.M. George. 1998. Probiotic activity of Aeromonas
media on the Pacific oyster, Crassostrea gigas, when challenged with Vibrio
tubiashii. Aquaculture, 169: 111-120.

Gladue, R. 1991. Rotifer and microalgae culture systems. Pages 276-286 in W. Fulks
and K.L. Main (Eds.), Proc. of a US-Asia Workshop, Honolulu, Hawaii, January
28-31, 1991. The Oceanic Institute, Hawaii.

Gopakumar, K. 1988. Quality control of molluscan products. Bulletin of Central
Marine Fishsheries Research Institute., 42 (2): 391-393.

Gopinathan, C.P. 1982. Methods of culturing phytoplankton. In: Manual of Research
methods for fish and shellfish nutrition. Central Marine Fisheries Research
Institute Special Publication: 8: 113-118.

Gopinathan, C.P. 1996. Live feed culture-micro algae. Bulletin of Central Marine
Fisheries Research Institute. 48: 110-116.

Granmo, A., B. Hemroth and O. Lindhal. 2001 . Marine bivalve farming-a sustainable
food production. Phuket Marine Biological Center Special Publication, 25(1):
179-188.

Gravely, F.H. 1941. Shells and and other remains found on the Madras beach. Groups
other than snails. (Mollusca and Gastropoda). Bull. Madras Govt. Mus. N.S.
Nat. Hist, 5(1): 1-112.

Grizel, H. and G. Tige. 1982. Evolution of the hemocytic disease casued by Bonamia
ostreae. Proc. Int. Colloq. Invertebr. Pathol., 3: 258-259.

Grizel, R.E., R. Langan and W.H. Howell. 1992. Growth responses of suspension¬
feeding bivalve molluscs to changes in water flow: differences between siphonate
and nonsiphonate taxa. Journal of Experimental Marine Biology and Ecology.,
162: 213-228.

Gross, F. and J.C. Smith. 1946. The decline of oyster populations. Nature, 157: 540-
542.

Guillard, R.R.L. 1959. Further evidence of the destruction of bivalve larvae by
bacteria. Biological Bulletin. (Woods Hole, Mass.). 117:258-266.

Gunter, G. 1979. Studies of the southern oyster borer, Thais haemastoma. Gulf
Research Reports, 6: 249-260.

Guo, X and S.K. Allen., Jr. 1994a. Reproductive potential and genetics of triploid
Pacific oysters, Crassostrea gigas (Thunberg). Biological Bulletin., 187: 309-3 1 8.

Guo, X. and S.K. Allen., Jr. 1994b. Viable tetraploids in the Pacific oyster ( Crassostrea
gigas Thunberg) produced by inhabiting polar body in eggs from triploids. Mol.
Mar. Biol. Biotechnol., 3(1): 42-50.

Guo, X., G.A. Debrosse and S.K. Allen., Jr. 1996. All— triploid Pacific oysters
(Crassostrea gigas Thunberg) produced by mating tetraploids and diploids.
Aquaculture, 142(3-4): 149-164.

Guo, X., S.E. Ford and F.Zhang. 1999. Molluscan Aquaculture in China. Journal of
Shellfish Research., 18(1): 19-31.

Haley, L.E. and G.F. Newkirk. 1982. The genetics of groWth rate of Crassostrea
viriginica and Ostrea edulis. Malacologia, 22: 399-401.

Hameed, PS. and A.L. Paulpandian. 1987. Feeding and digestive rhythms in intertidal
bivalve molluscs, Anadara rhombea (Born) and Crassostrea madrasensis
(Preston). Indian Journal of Marine Sciences.,. 16(3): 151-154.

References

207

Hand, R.E. and J.A. Nell. 1999. Studies on triploid oysters in Australia. XII. Gonad
discolouration and meat condition of diploid and triploid Sydney rock oysters
( Saccostrea commercialism in five estuaries in New South Wales, Australia.
Aquaculture, 171: 181-194.

Hand, S.C. and W.B. Stickle. 1977. Effects of tidal fluctuations of salinity on pericardial
fluid composition of the American oyster, Crassostrea virginica. Marine Biology.
42:259-272.

Harding, J.M and R. Mann. 1999. Fish species richness in relation to restored oyster
reefs, Piankatank river, Virginia. Bulletin of Marine Sciences., 65(1): 289-300.

Harry, H.W. 1985. Synopsis of the superspecifie classification of living oysters
(Bivalvia:Gryphaeidae and Ostreidae). Veliger, 28:121-158.

Harry, H. W. 1986. The relevancy of generic concept to the geographic distribution of
living oysters (Gryphaeidae and Ostreidae). American Malcological Bulletin. 4:
157-162.

Haskin, H.H., W.J. Canzonier and J.L. Myhre. 1965. The history of “MSX” on
Delaware Bay oyster grounds, 1957-1965. American Malacological Union
Bulletin., 32:20-21 (Abstract).

Haskin, H.H. and S.E. Ford. 1988. Characteristics of inbred oyster strains selected for
resistance to Haplosporidium nelsonii (MSX). Journal of Shellfish Research.,
7:162 (Abstract).

Hathaway, R.R. 1958. The crown conch Melongena corona Gmelin: its habits, sex
ratios and possible relations to the oyster. Proceeding of National Shellfish
Association.,* 48: 189-194.

Haven, D. 1959. Effects of pea crabs Pinnotheres ostreum on oysters Crassostrea
virginica. Proceeding of National Shellfish Association., 49:77-86.

Haven, D.S. and R. Morales-Alamo. 1970. Filtration of particles from suspension by
the American oyster Crasssostrea virginica. Biological Bulletin., 139: 248-264.

Haven, D.S., W.J. Hargis, Jr. and PC. Kendall. 1978. The oyster industry of Virginia:
Its status, problems and promise. VIMS Special papers in Marine Science Sea
Grant Programme, Gloucester Point, Virginia.

Havenaar, R. and J.H.J. Huis int Veld. 1992. Probiotics: a general view. Pages 151-169
in B.J.B. Wood (ed.) The Lactic Acid Bacteria. Vol. \. Elsevier, London.

Hawkins, C.M., T.W. Rowell and P. Woo. 1987. The importance of cleansing in the
calculation of condition index in the soft-shell clam, Mya arenaria (L.). Journal
of Shellfish Research., 69:29-36.

Hawkins, A.J.S, R.F.M. Smith, B.L. Bayne and M. Heral. 1996. Novel observations
underlying the fast growth of suspension feeding shellfish in turbid environments:
Mytilus edulis. Mar. Ecol. Prog. Ser., 131:179-190.

Hawkins, A.J.S. , B.L. Bayne, S. Bougrier, M. Heral, J.I.P. Iglesias, E. Navarro, R.F.M,
Smith and M.B. Urrutia. 1998. Some general relationships in comparing the
feeding physiology of suspension-feeding bivalve molluscs. Journal of
Experimental Marine Biology and Ecology., 219: 87-103.

Haws, M.C. and L. Dimichele. 1993. Epinephrine as an experimental tool for the study
of metamorphosis. World Aquaculture., 24(3): 25-29.

Hedgecock, D and N.B. Okazaki. 1984. Genetic diversity within and between
populations of American oysters ( Crassostrea ). Malacologia., 25: 535-549.

208

Oyster Biology and Culture in India

Hedgecock, D., K. Cooper and W. Hershberger, 1991. Genetic and environmental
components of variance in harvest body size among pedigreed Pacific oysters,
Crassostrea gigas from controlled crosses. Journal of Shellfish Research., 10:
516 (Abstract).

Hedgpeth, J.W. 1953. An introduction to the Zoogeography of the Northwestern Gulf
of Mexico with reference to the invertebrate fauna. Publications of the Institute
of Marine Science, University of Texas. ,3: 107-224.

Helm, M.M., D.L. Holand, S.D. Utting and J. East. 1991. Fatty acid composition of
early non-feeding larvae of the European oyster, Ostrea edulis L. Journal of
Marine Biological Association. U.K., 17: 673-684.

Henderson, B.A. 1982. Practical methods of handling and remote setting eyed-
pediveliger larvae of the Pacific oyster, Crassostrea gigas (Thunberg). Journal
of Shellfish Res., 2(1): 119-120.

Heral, M. and Deslous-Paoli, J.M. 1991. Oyster culture in European countries. Pages
153-190. In W. Menzel (Ed.), Estuarine and Marine Bivalve Mollusk Culture,
CRC Press, Boston.

Heral, M., J.M. Deslous-Paoli and J.M. Somin. 1983. Transferts energetiques entre
l’huitre Crassostrea gigas et la nourriture potentielle disponible dans un basin
ostreicole: premiere approaches. Oceanis, 9(3): 169-194.

Hershberger, W.K., J.A. Perdue and J.H. Beattie. 1984. Genetic selection and systematic
breeding in Pacific oyster culture. Aquaculture, 39: 237-245.

Higgins, E. 1938. Progress in biological inquiries. 1937. Bulletin U.S. Bureau of
Fisheries, Administrative Report No. 30: 1-70.

Higgins, P.J. 1980a. Effects of food availability on the valve movements and feeding
behavior of juvenile Crassostrea viriginca (Gmelin).I. Valve movements and
periodic activity. Journal of Experimental Marine Biology and Ecology., 45:229-
244.

Higgins, P.J. 1980b. Effects of food availability on the valve movements and feeding
behavior of juvenile Crassostrea virginica (Gmelin).II. Feeding rates and
behaviour. Journal of Experimental Marine Biology and Ecology., 46: 17-27.

Hill, B.J., and D.J. Alderman. 1979. Observations on the experimental infection of
Ostrea edulis with two molluscan viruses. Haliotis, 8:297-299.

Hoese, H.D. and D. Hoese. 1967. Studies on the biology of the feeding reaction in
Gobiosoma bosci. Tulane Stud. Zool., 14: 55-73.

Hofstetter, R.P. 1977. Trends in population levels of the American oyster Crassostrea
virginica Gmelin on public reef in Galveston Bay. Texas. Texas Parks and
Wildlife Dept., Technical Series 24. 90 pp.

Holliday, J.E. 1992. International developments in oyster hatchery technology.
Miscellaneous Bulletin 1, Division of Fisheries, Department of Agriculture,
New South Wales, 122 pp.

Holliday, J.E., G.L. Allen and J. Frances. 1991. Cold storage effects on setting of
larvae of the Sydney rock oyster, Saccostrea commercialis and the Pacific
oyster Crassostrea gigas. Aquaculture, 92: 179-185.

Homell, J. 1910a. Note on an attempt to ascertain the principal determining factor in
oyster spawning in Madras backwaters (Madras Fish. Investigation, 1908)
Madras Fisheries Bulletin., 4: 25-31.

References

209

Hornell, J. 1910b. Report on the suitability of Pulicat Lake for oyster culture. Madras
Fisheries Bulletin., 4: 1-23.

Hornell, J. 1916. The utilization of corals and shells for lime burning in the Madras
Presidency. Madras Fisheries Bulletin., 8: 105-126.

Hornell, J. 1917. The edible molluscs of the Madras Presidency. Madras Fish. Bulletin.,
11: 1-51.

Hornell, J. 1949. The study of Indian molluscs. Journal of Bombay Natural History
Society., 48: 303-334. 543-569 and 750-774.

Howell, M. 1966. A contribution to the life history of Bucephalus longicornutus
(Manter, 1954), Zool. Publ. Victoria Univ. N.Z., 40: 42p.

Howell, M. 1967. The trematode, Bucephalus longicornutus (Manter, 1954) in the
New Zealand mud-oyster, Ostrea lutaria. Trans. R. Soc. N.Z., 8:221-237.

Hsia, S.C. 1950. Effect of silt upon Ostrea virginica. Hawaiian Academy of Science,
25:8-9.

Hu, Y.P., R.A. Lutz and R.C. Vrijenhoek. 1993. Overdominance in early life stages of
an American oyster strain. Journal of Hered., 84: 254-258.

Hu-Jiachai., Zhong-Youping and Wang-Liquing. 1995. The technological research on
shrimp and oyster mixed culture in the penaeid pond. Journal Xiamen-Fish-
Coll. Xiamen-Shuichan-Xueyuan-Xuebao. 17(2): 22-26. Journal of Shellfish
Research., 8: 319 (Abstract).

Hunter, A.C. and C.W. Harrison. 1928. Bacteriology and chemistry of oysters, with
special reference to regulatory control of production, handling, and shipment.
U.S. Department of Agriculture, Technical Bulletin No. 64: 75 pp.

Iglesias, J.I.P., M.B. Urratia, E. Navarro and I. Ibarrola. 1998. Measuring feeding and
absorption in suspension-feeding bivalves: An appraisal of the biodeposition
method. Journal of Experimental Marine Biology and Ecology., 219:71-86.

Imai, T. 1977. Aquaculture in shallow seas. Amerind Publishing Co. Private Ltd. New
Delhi. 615 pp.

International Commission on Zoological nomenclature 1955. Opinion 338. Acceptance
of the mesozoic fossil species Gryphaea areata Lamarck, 1801, as the type
species of the nominal genus Gryphaea Lamarck, 1801, and addition of the
generic name Gryphaea Lamarck, 1801 (Class Pelecypoda) to the official List
of Generic Names. Opinions and declarations rendered by the International
Commission on Zoological Nomenclature, 10 (5): 125-180.

Jakob, G.S., G.D. Pruder and J.K. Wang. 1993. Growth trial with the American oyster
Crassostrea virginica using shrimp pond water as feed Journal of World
Aquaculture Society., 24(3): 344-351.

James, P.S.B.R. and K.A. Narasimham. 1993. Handbook on Aquafarming: Molluscs.
Marine Products Development Authority of India, Cochin. 91 pp.

Jasmine, G.I., C.B.T. Rajagopalaswamy and G. Jegathesan. 1988. Mercury level in the
edible oyster, Crassostrea madrasensis. Bulletin of Central Marine Fisheries
Research Institute., 42(2): 414-416.

Jayachandran, P, G. Sukumar and G. Jeyasekaran. 1998. Utilisation of the edible
oysters, Crassostrea madrasensis- preparation of certain value added products.
Bulletin of Central Marine Fisheries Research Institute. 42(2): 387-390.

210

Oyster Biology and Culture in India

Jeffs, A.G., S.H. Hooker and R.G. Creese. 1997. Variability in life history characters
of the Chilean oyster Tiostrea chilensis (Philippi, 1845). New Zealand Journal
of Marine Freshwater Research , 3(4):487-495. (Abstract).

Jones, S. 1968. The molluscan fishery resources of India. Proceedings of Symposia.
Mollusca; Marine Biological Association of India, Pt III: 906-918.

Jones, A.B. and N.P. Preston. 1999. Sydney rock oyster, Saccostrea commercial^
(Iredale and Roughley), filtration of shrimp farm effluent: the effects on water
quality. Aquaculture Research, 30: 51-57.

Jones, A.B., W.C. Dennison and N.P. Preston. 2001. Integrated treatment of shrimp
effluent by sedimentation, oyster filteration and macroalgal absorption: a
laboratory scale study. Aquaculture, 193: 155-178.

Jones, G. and B. Jones. 1988. Advances in the remote setting of oyster larvae. Ministry
of Agriculture and Fisheries. Victoria, B.C. (Canada). 88 pp.

Jones, T.O., G.K. Iwama. 1991. Polyculture of the Pacific oyster, Crassostrea gigas
(Thunberg), with Chinook salmon, Oncorhynchus tshawytscha. Aquaculture,
92: 313-322.

Joseph, M.M. 1978. Observations on the larval termatode Bucephalus sp. parasitic in
the oyster Crassostrea madrasensis (Preston) Journal of Invertebrate Pathology.,
32:381-383.

Joseph, M.M. 1989. Mussel and oyster culture in Thailand. Out of shell, 1:10-15.

Joseph, M.M. 1998. Mussel and oyster culture in the tropics. Pages 309-360 in
Tropical Mariculture. Academic Press.

Joseph, M.M and M.N. Madhyastha. 3982. Gametogenesis and somatic versus gonadal
growth in the oyster, Crassostrea madrasensis (Preston). Indian Journal of
Marine Sciences., 11: 303-310.

Joseph, M.M and S.Joseph. 1983. Some aspects of experimental culture of the oyster
Crassostrea madrasensis (Preston). Proceedings of Symposium on Coastal
Aquaculture., 2: 451-455.

Joseph, M.M. and S.Joseph. 1985. Age and growth of the oyster Crassostrea
madrasensis (Preston) in Mulki estuary, West coast of India. Indian Journal of
Marine Sciences., 14(4): 184-186.

Joseph, M.M. and S. Joseph. 1988. Biotic potential and environmental resistance of
bivalves of Mangalore coast. Bulletin of Central Marine Fisheries Research
Institute., 42(1) .205-210.

Kafuku, T and H. Ikenoue. 1983. Modern methods of Aquaculture in Japan. Pages
143-182 Elsevier Scientific Publishing Company. Amsterdam.

Kandasamy, D. and P. Muthiah. 1988. Microencapsulated diet for larvae and spat of
Crassostrea madrasensis. Bulletin of Central Marine Fisheries Research
Institute., 42(2): 354-358.

Karunasagar. I., H.S.V. Gowda, N. Subburaj, M.N. Venugopal and I. Karunasagar.
1984. Outbreak of paralytic shellfish poisoning in Mangalore, West coast of
India. Current Science, 53(5): 247-249.

Karunasagar, I., K. Segar and I. Karunasagar. 1989. Incidence of PSP and DSP in
shellfish along the coast of Karnataka State (India). Pages 61-64. in T.Okaichi,
D.M. Anderson andT.Nemoto (Eds.), Red Tides: Biology, Environmental Science
and Toxicology. Elsevier, New York, USA.

References

211

Karunasagar, I., B. Joseph, K.K. Philipose and I. Karunasagar. 1998. Another outbreak
of PSP in India. The Intergovernmental Oceanographic Commission of UNESCO.
Harmful Algae News, 17:1.

Keck, R., D. Maurer, L. Waiting. 1973. Tidal stream development and its effect on the
distribution of the American oyster. Hydrobiology, 42:369-379.

Kennedy, V.S. 1983. Sex ratios in oysters, emphasizing Crassostrea virginica from
Chesapeake Bay, Maryland. Veliger, 25(4):329-338.

Kennedy, V.S. 1996. Biology of larvae and spat. Pages 371 -411. In V.S. Kennedy,
R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster Crassostrea virginica,
published by the Maryland Sea Grant College, University of Maryland System,
College Park.

Keogh, J.A., G. Bremner, A.W.J. Frazer and D.J. Fletcher. 1997. Effects of treatment,
site and time of reseeding on survival and growth in the bluff oyster, Tiostrea
chilensis (Bivalvia: Ostreidae) Philippi 1845. Journal of Shellfish Research ., 16
(l):267-268. (Abstract).

Klinbunga, S., P. Ampayup, A. Tassanakajon, P. Jarayabhand, and W. Yoosukh. 2000.
Development of Species-Specific Markers of the Tropical Oyster ( Crassostrea
belcheri ) in Thailand. Marine Biotechnology., 2(5) : 476-484

Ko, R.C., B. Morton and P.S. Wong. 1975. Prevalence and histopathology of
Echinocephalus sinensis (Nematoda: Gnathostomatidae) in natural and
experimental hosts. Canadian Journal of Zoology., 53:550-559.

Koganezawa, A. 1975. Present status of studies on the mass mortality of cultured
oysters in Japan and its prevention. Proc. US.-Jpn. Meet. Aquaculture, 3:29-34.

Koles, T. and K.T. Paynter. 1999. Oyster restoration in Maryland; Measuring progress
and productivity. Journal of Shell ish Research. 18 (1) (Abstract) .

Komaru, A., Y. Uchimuta, H. Ieyama and K.T. Wada. 1988. Detection of induced
triploid scallop, Chlamys nobilis, by DNA microfluorometry with DAPI staining.
Aquaculture, 69: 201-209.

Korringa, P. 1952. Recent advances in oyster biology. Q. Rev. Biol., 27: 266-308 and
339-365.

Korringa, P. 1976a. Farming the cupped oysters of the genus Crassostrea. Developments
in Aquaculture and Fisheries Science, 2. Elsevier Scientific Publishing Company.
Amsterdam: 219 pp.

Korringa, P. 1976b. Farming the flat oysters of the genus Ostrea. Developments in
Aquaculture and Fisheries Science, 3. Elsevier Scientific Publishing Company.
Amsterdam: 238 pp.

Krantz, G.E. and J.V. Chamberlin. 1978. Blue crab predation on cultchless oyster spat.
Proceedings of National Shellfish Association., 68: 38-41.

Kripa, V. 1998. Studies on the biology and experimental culture of the rock oyster
Saccostrea cucullata (Born). Ph.D Thesis. Cochin University of Science and
Technology. 216 pp.

Kripa, V. and K.Y.M. Salih. 1999a. Oyster resources of Ashtamudi Lake, south west
coast of India.Pages 367-369. Proceeding of Fourth Indian Fisheries Forum.

Kripa, V. and K.Y.M. Salih. 1999b. Growth and reproduction of the rock oyster,
Saccostrea cucullata (Born) in Ashtamudi Lake, Kerala. Pages 371-372
Proceedings of Fourth Indian Fisheries Forum .

212

Oyster Biology and Culture in India

Kripa, V., K.S. Mohamed, T.S. Velayudhan, P. Laxmilatha, P. Radhakrishnan, M.
Joseph, P.S. Alloycious, J. Sharma and K.K. Appukuttan. 2001. Recent
developments in edible bivalve farming in India. Aquaculture Asia, 6(4): 40-43.

Kripa. V., K.K. Appukuttan, T.S. Velayudhan, K.S. Mohamed, P.S. Alloycious,
PRadhakrishnan, M.Joseph, and J. Sharma 2004 . Oyster farming a rural
development program in Kerala. Mar. Fish. Infor.Ser.T&E Ser, No. 180, p 1-6.

Laing, I. 1987. The use of artificial diets in rearing bivalve spat. Aquaculture, 65:
243-249.

Laing, I. 1991. Cultivation of marine unicellular algae. Laboratory Leaflet Number 67.
Directorate of Fisheries Research, Lowestoft, U.K. 31 pp.

Lakshmanan, P.T. 1988. Heavy metals in commercially processed molluscan products
in relation to quality. Bulletin of Central Marine Fisheries Research Institute .,
42(2): 417-422.

Lalta, S and P. Espeut. 1991. Transforming a biology project into rural development:
Lessons form the oyster culture project in Jamaica. Pages 147-162 in G.F.
Newkirk and B.A. Field (Eds.), Oyster culture in the Caribbean. Proceedings of
a workshop 19-22 November 1990 at Kingston Jamaica Mollusc Culture ,
Newtwork, Halifax Canada.

Landers, W.S. and E.W. Rhodes., Jr. 1970. Some factors influencing predation by the
flatworm Stylochus ellipticus (Girard) on oysters. Chaesapeake Sci., 11: 55-60.

Langdon, C.J. 1982. New techniques and their application to studies of bivalve
nutrition, in G.D. Purder, C.J. Langdon and D.E. Conklin (Eds.), Second
International Conference on Aquaculture Nutrition: Biochemical and
Physiological Approaches to Shellfish Nutrition , Louisiana State University,
Baton Rouge, pp. 305-320.

Langdon, C.J. 1989. Preparation and evaluation of protein microcapsules for marine
suspension-feeder, the Pacific oyster Crassostrea gigas. Marine Biology., 102:
217-224.

Langdon, C.J. and M.J. Waldock. 1981. The effect of algal and artificial diets on the
growth and fatty acid composition of Crassostrea gigas spat. Journal of Marine
Biological Association. U.K., 61: 431-448.

Langdon, C.J. and E.T. Bolton. 1984. A microparticulate diet for a suspension feeding
bivalve mollusc Crassostrea virginica (Gmelin). Journal of Experimental Marine
Biology and Ecology., 82: 239-258.

Langdon, C.J. and R.I.E. Newell. 1996. Digestion and nutrition in larvae and adults.
Pages 231-269 in V.S. Kennedy, R.I.E. Newell and A.F. Eble (Eds.), The
Eastern oyster Crassostrea virginica, published by the Maryland Sea Grant
College, University of Maryland System, College Park.

Lannan, J.E. 1980. Broodstock management of Crassostrea gigas. IV. Inbreeding and
larval survival. Aquaculture, 21: 353-356.

Lauckner, G. 1983. Diseases of Mollusca: Bivalvia. Pages 477-961 in O Kinner (ed.)
Diseases of Marine Animals. Biol. Anst. Helgol. Hamburg, FRG.

Lawrence, D.R. and C.M. Gordan. 1988. The determination and use of condition index
of oysters. Estuaries, 5:23-27.

Leitao., A. P. Boudry and C. Thiriot - Quievreux. 2001. Negative correlation between
aneuploidy and growth in the Pacific oyster, Crassostrea gigas: ten years of
evidence. Aquaculture, 193: 39 - 48.

References

213

Levine, N.D. 1978. Perkinsus gen. N. and other new taxa in the protozoan phylum
Apicomplexa. Journal of Parasitology., 64: 549.

Levine, N.D. and 15 co-authors. 1980. A newly revised classification of the Protozoa
Journal of Protozoology., 27: 35-58.

Lewis, E.J. 1993. Transmission studies of a disease affecting juvenile oysters,
Crassostrea virginica Gmelin, in the northeastern United States. M.S. Thesis.
University of Maryland, College Park, Maryland. 105pp.

Librero, A.R., R.A. Callo, S.P. Dizon and E.R. Pamulaklakin. 1976. Socio-economic
survey of the Aquaculture industry of the Philippines: Oyster seafarming, a
socio-economic study. Singapore; Southeast Asian Fisheries Development Center,
SEAFDEC-PCARR Research paper series 6: 101 pp.

Lipovsky, V.P and K.K. Chew. 197 1 . A preliminary report on Pacific oyster (Crassostrea
gigas ) mortality after transfer from a natural bed into 10°C and 20°C water in the
laboratory. Proceeding of National Shellfish Association. 61: 9.

Little, J.W., S.H. Hopkins and F.G. Schlicht. 1966. Acanthoparyphium spinulosum
(Trematoda: Echinodermatidae) in oysters at Port Isabel, Texas. Journal of
Parasitology. 52: 663.

Littlewood, D.T.J. 1991. Pests and predators of cultivated mangrove oysters. Pages
109 -146 in G.F. Newkirk and B.A. Field (Eds.), Oyster culture in the Caribbean.
Proceedings of a workshop 19-22 November 1990 at Kingston, Jamaica, Mollusc
Culture Newtwork, Halifax Canada.

Littlewood, D.T.G. and C. Donovan. 1988. Sex ratio, condition and glycogen content
of raft cultivated mangrove oysters Crassostrea rhizophorae Journal of Shellfish
Research 7(3): 395-399.

Littlewood, D.T.J. and S.E. Ford. 1990. Physiological responses to acute temperature
elevation in oysters, Crassostrea virginica (Gmelin, 1791), parasitized by
Haplosporidium nelsoni (MSX) (Haskin, Stauber and Mackin, 1966). Journal
of Shellfish Research. 8: 159-164.

Logie, R.R. 1956. Oyster mortalities, old and new, in the Maritimes. Fish Res. Board
Can., Prog. Rep. Atl. Coast. Stn. 65:3-11.

Loosanoff, V.L. 1953. Behavior of oysters in water of low salinities. Proceedings of
National Shellfish Association. 43:135-151.

Loosanoff, V.L. 1962. Effects of turbidity on some larval and adult bivalves. Proc.
Gulf Carib. Fish. Inst. 14:80-95.

Loosanoff, V.L. and F.D. Tommers. 1948. Effect of suspended silt and other substances
on rate of feeding oysters. Science. 107: 69-70.

Loosanoff, V.L. and H.C. Davis. 1952a. Repeated semiannual spawning of northern
oysters. Science. 115: 675-676.

Loosanoff, V.L. and H.C. Davis. 1952b. Temperature requirement for maturation of
gonads of northern oysters. Biol. Bull. Woods Hole 103: 80-96.

Loosanoff, V.L., and H.C.Davis. 1963 . Rearing of bivalve molluscs. Advances in
Marine Biology. 1: 1-136.

Longwell., A.C. and S.S. Stiles. 1996. Chromosomes, biology and breeding. Pages
443-465 inV.S. Kennedy., R.I.E. Newell and A.F. Eble (Eds.), The Eastern
Oyster Crassostrea virginica. Maryland Sea Grant College System, College
Park.

214

Oyster Biology and Culture in India

Mackenzie, C.L., Jr. 1970. Causes of oyster spat mortality, condition of oyster setting
beds and recommendation for oyster bed management. Proceedings of National
Shellfish Association. 60: 59-67.

Mackenzie, C.L., Jr. 1981. Biotic potential and environmental resistance in the American
oyster ( Crassostrea virginica ) in Long Island Sound. Aquaculture 22: 229 -268.

Mackenzie, C.L., Jr. 1983. To increase oyster production in the northern United States.
Marine Fisheries Review 45(3): 1-22.

Mackenzie, C.L., Jr. 1989. Enhancing molluscan shellfisheries. Mar. Fish. Rev. 51 (3):
1-47.

Mackenzie, C.L., Jr. 1996. Management of natural populations. Pages 709-719 in V.S.
Kennedy, R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster Crassostrea
virginica, published by the Maryland Sea Grant College, University of Maryland
System, College Park.

Mackin, J.G., H.M. Dwen and A. Collier. 1950. Preliminary note on the occurrence of
a new protistan parasite, Dermocystidium marinum in Crassostrea virginica
(Gmelin). Science III: 328-329.

Mahadevan, S. 1987. Oyster resources of India. Bulletin of Central Marine Fisheries
Research Institute. 38:14-16.

Mahadevan, S. and K.N. Nayar. 1987. Ecology of oyster beds. Bulletin Central
Marine Fisheries Research Institute. 38: 7-14.

Mahadevan, S., K.N. Nayar and P. Muthiah. 1980. Oyster farming. Marine Fisheries
Information Services, Technical and Extension Services. 26: 1-3.

Mallet., A.L. and L.E. Haley. 1984. General and specific combining abilities of larval
and juvenile growth and viability estimated from natural oyster populations.
Marine Biology. 81: 53 - 59.

Malcouf, R.E., and V.M. Bricelj. 1989. Comparitive biology of clams: Environmental
tolerance, feeding and growth. Pages 23-37 in Manzi, J.J. and Castagna, M.
(Eds.), Clam Mariculture in North America, Elseveir publication, New York.

Mane, U.H., and R. Nagabhushanam. 1976. A study on the reproductive biology of the
Indian oyster, Crassostrea gryphoides. Natural Sciences Journal, University of
Aurungabad. 15(8): 245-258.

Mane, U.H., M.S. Kachole and S.S. Pawar. 1979. Effect of pesticides and narcotants
on bivalve molluscs. Malacologia 18: 347-360.

Mane, U.H. and R. Nagabhushanam. 1988. Reproduction in edible bivalve shellfishes
of Ratnagiri coast. Bulletin of Central Marine Fisheries Research Institute.
42(1): 167-176.

Maroun., L.E, M. Degner, M.E. Mourey, D.F. Rowan and K.S. Amankwah. 1986.
Increased mortality and aneuploidy in embryos from rabbits injected with
Newcastle disease virus at the time of ovulation and conception. Teratology 34:
201 - 206.

Marteil, L. 1968. La maladie des branchies. Int. Counc. Explor. Sea. Doc. C.M.1968/
K, 5.

Marty, Y., F.Delaunay, J.Moal and J.F.Samain. 1992. Changes in the fatty acid
composition of Pecten maximus (L.) during larval development. Journal of
Experimental Marine Biology and Ecology. 163: 221-234.

References

215

Mathers, N.F. 1973. A comparative histochemical survey of enzymes associated with
the process of digestion in Ostrea edulis and Crassostrea angulata (Mollusca:
Bivalvia). J. Zool. 169:169-179.

Matthiessen, G.C.1989. Small- scale oyster farming - a manual. National Coastal
Resources Research and Development Institute, Newport, OR, USA: 82pp.

Matthiessen, G.C., S.Y. Feng and L. Leibovitz. 1990. Pattern of MSX (. Haplosporidium
nelsoni ) infection and subsequent mortality in resistant and susceptible strains
of the eastern oyster Crassostrea virginica (Gmelin, 1791), in New England.
Journal of Shellfish Research. 9: 359-366.

May, E.B. and D.G. Bland. 1969. Survival of young oysters in areas of different
salinity in Mobile Bay: Proc. Southeastern Association of Game and Fish
Commissioners, 23:519-521.

Mayasich, S.A. and R.A. Smucker 1987. Role of Cristispira sp. and other bacteria in
the chitinase and chitobiase activities of the crystalline style of Crassosrtea
virginica (Gmelin). Microb. Ecol. 14:157-166.

Me Comick-Ray, M.G. 1 998. Oyster reefs in 1 878. Seascape pattern- Winstow Revisited.
Estuaries 21 (4B): 784-800.

Mee, L.D., M. Espinosa and G. Diaz. 1986. Paralytic shellfish poisoning with a
Gymnodinium catenatum red tide on the Pacific coast of Mexico. Marine
Environmental Research. 19: 77-92.

Menzel., R.W. 1973. Some species affinities in the oyster genus Crassostrea. Bulletin
of American Malcology Union. 38. (Abstract).

Menzel, R.W. and S.H. Hopkins 1955. Effects of two parasites on the growth of
oysters. Proceeding of Natural Shellfish Association. 45:184-186.

Menzel, R.W., N.C. Hulings and R.R. Hathaway. 1958. Causes of depletion of oysters
in St. Vincent Bar, Apalachicola Bay, Florida. Proceedings of National Shellfish
Association. 48: 66-71.

Menzel, R.W. and F.E. Nichy. 1958. Studies on the distribution and feeding of some
oyster predators in Alligator Harbour, Florida. Bulletin of Marine Science Gulf
arribean. 8: 125-145.

Meyers, T.R. 1979. A reo-like virus isolated from juvenile American oysters
( Crassostrea virginica ). Journal of General Virology. 43:203-212.

Meyers, T.R. 1981. Endemic diseases of cultured shellfish of Long Island, New York:
Adult and juvenile American oysters ( Crassostrea virginica ) and hard clams
( Mercenaria mercenaria). Aquaculture 22:305-330.

Meyers, T.R., and K. Hirai. 1980. Morphology of reo-like virus isolated from juvenile
American oysters, Crassostrea virginica. Journal of General Virology. 46:249-253 .

Millican, P.F. and M.M. Helm. 1994. Effect of nutrition on larvae production in the
European flat oyster, Ostrea edulis. Aquaculture 123: 83-94.

Mobius, K. 1883.XXVII. The oyster and oyster culture-Translated by H.J. Rice by
permission of the author from the book published in 1887. Pages 683-751 Die
auster and die Austernwinthschaft Verlag Von Wiegandt Hempel and Parey,
Berlin: U.S. Commission of Fish and Fisheries, Part 8. Report of the
Commissioner for 1 880, Appendix H.

Moore. H.E. 1898. Oysters and methods of oyster culture with notes on clam culture.U.S.
Comm. Fish and Fisheries. Part 23. Report of the Commissioner for 1897:
263-340.

216

Oyster Biology and Culture in India

Morel, M. and C. Tige. 1974. Maladie de la glande digestive de Fhitre plate. Bull. Inst.
Peek. Marit. Maroc. 241:33-40.

Mori, T. 1935. Mytilicola orientalis, a new species of parasitic copepoda Dobutsugaku
Zasshi. 47: 687-690. (in Japanese; English summary).

Mori, K., T. Imami., K. Toyoshima and I. Usuki. 1965. Studies on the mass mortality
of the oyster in Matsushima Bay. Changes in the physiological activity and the
glycogen content of the oyster during the stages of sexual maturation and
spawning. Tohoku-ku Suisan Kenkyusho Kenkyu Hokoku, 25: 49-63.

Morrison, C.M. 1996. Adductor muscle and musculature. Pages 169-181 in V.S.
Kennedy, R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster Crassostrea
virginica, published by the Maryland Sea Grant College, University of Maryland
System, College Park.

Morton, B.S. 1971. The diurnal rhythm and tidal rhythm of feeding and digestion in
Ostrea edulis. Biol. J. Linnean Soc. Lond. 3: 329-342.

Moses, S.T. 1928. A preliminary report on the anatomy and life history of the common
edible backwater oyster Ostrea madrasensis. Journal of Bombay Natural History
Society. 32: 548-552.

MPEDA 2000. Statistics of Marine Products Exports. 34 pp

Muthiah, P. 1987. Techniques of collection of oyster spat for farming. Bulletin of
Central Marine Fisheries Research Institute. 38: 48-51.

Muthiah, P and K.N.Nayar. 1988. Incidence of Perkinsus marinus in Crassostrea
madrasensis. Bulletin of Central Marine Fisheries Research Institute. 42: 232-236.

Muthiah, P., D, Sundararajan, GSreenivasan and N.Vaithinathan. 1987. Pests and
predators of oysters. Bulletin of Central Marine Fisheries Research Institute.
38: 71-75.

Muthiah, P, M.E.Rajapandian, K.Ramadoss, K.K.Appukuttan and T.S.Velayudhan.
2000. The edible oyster culture. Pages 786-801. In V.N.Pillai and N.GMenon
(Eds.) Marine Fisheries Research and Management, Central Marine Fisheries
Research Institute, Cochin.

Nair N.B., P.K. Abdul Azis, K. Dharamaraj, M. Arunachalam, K. Krishnakumar and
N.K. Balasubramanian. 1984. Ecology of Indian estuaries - V: Primary
productivity of the Ashtamudi estuary, south-west coast of India. Proceedings
of Indian Academy of Science (Anim. Sci.). 93 (1): 9 - 23.

Nair, U.N. and N.B. Nair. 1985. Height-Depth (Breadth) relationship of shells in the
backwater oyster Crassostrea madrasensis (Preston) of the Cochin Harbour.
Fishery Technology 22: 87-91.

Nair, D., R. Hall and C.L. Angell, 1993. Oyster culture on the west coast of Peninsular
Malaysia. BOBP Report 63, Madras, India: 32pp.

Nair, M. K. R. and S. Girija. 1993. Edible oysters- Present status of product development
and domestic market potential. Mar. Fish. Infor. Ser. T&E, No. 125: 10-17.

Narasimham, K.A. 1987. Biology of Crassostrea madrasensis of Kakinada. Bulletin
of Central Marine Fisheries Research Institute. 38: 40-48.

Narasimham., K.A. 1998. Aspects of hatchery production of bivalve seed. In: Hameed,
M.S. and Kurup; B.M. (Eds.), Technological Advancements in Fisheries.
Publication: No. 1 School of Indl. Fish., Cochin University of Science and
Technology, Cochin.

References

217

Narasimham, K.A., V. Kripa and K.Balan. 1993. Molluscan shellfish resources of
India - An overview. Indian Journal of Fisheries. 40(3): 112-124.

Navarro, E., J.I.P Iglesias, A. Perez-Camacho, U. Labarta, R. Beiras. 1991. The
physiological energetics of mussels ( Mytilus galloprovincialis Lmk.) from
different cultivation rafts in the Ria de Arosa (Galicia, N.W.Spain). Aquaculture
94:197-212.

Nayar, K.N. 1987. Technology of oyster farming. Bulletin of Central Marine Fisheries
Research Institute. 38: 59-62.

Nayar, K., Nagappan, M.E. Rajapandian, A.D. Gandhi and C.P. Gopinathan. 1982.
Induced spawning and larval rearing of Crassostrea madrasensis (Preston) in
the laboratory. Mar. Fish. Infor. Ser. T&E, No. 44: 14-16.

Nayar, K.N. and S. Mahadevan. 1983. Oyster culture at Tuticorin. Proceeding of
Symposia. Coastal Aquaculture 2: 475-478.

Nayar, K.N., M.E. Rajapandian and D.C.V. Easterson. 1983. Purification of farm
grown oysters. Proceedings of Symposia. Coastal Aquaculture, Mar. Biol. Ass.
India. 2: 505-508.

Nayar, K.N., M.E. Rajapandian, A.D. Gandhi and C.P. Gopinathan. 1984. Larval
rearing and production of spat of the oyster Crassostrea madrasensis (Preston)
in an experimental hatchery. Indian Journal of Fish., 31: 233-243.

Nayar, K.N., S. Mahadevan and P.Muthiah. 1987a . Economics of oyster culture.
Bulletin of Central Marine Fisheries Research Institute. 38: 67-70.

Nayar, K.N., K.S.Rao, M.E.Rajapandian, C.P.Gopinathan and A.D. Gandhi. 1987b.
Production of oyster seed in a hatchery system. Bulletin of Central Marine
Fisheries Research Institute. 38: 52-58.

Nayar, K.N., K.S.Rao, P.Muthiah and M.E.Rajapandian. 1988 a. Recent trends in
oyster culture in India. Bulletin of Central Marine Fisheries Research Institute.
42(2): 271-275.

Nayar, K.N., K.S. Rao, M.E. Rajapandian and A.D. Gandhi. 1988b. Induced maturation
and spawning of Crassostrea madrasensis. Bulletin of Central Marine Fisheries
Research Institute. 42(2): 330-333.

Nayar, K.N., M.E. Rajapandian, C.P. Gopinathan and A.D. Gandhi. 1988c. Influence
of salinity and different algal diets on rearing of larvae of Crassostrea madrasensis
in hatchery. Bulletin of Central Marine Fisheries Research Institute. 42(2): 333-
336.

Nell, J. A., E. Cox, I.R. Smith and G.B. Maguire. 1994. Studies on triploid oysters in
Australia, the farming potential of Sydney rock oysters Saccostrea commercialis
(Iredale and Roughley). Aquaculture. 126: 243-255.

Nell, J.A., A.K. Sheridan and I.R. Smith. 1996. Progress in a Sydney rock oyster
Saccostrea commercialis (Iredale and Roughley) breeding programme.
Aquaculture. 144: 295-302. *

Nelson.T.C. 1938. The feeding mechanism of the oyster. 1. On the pallium and the
branchial chambers of Ostrea virginica, O.edulis and O. angulata with
comparison with other species of the genus. Journal of Morphology. 63: 1-61.

Newell, R.I.E. 1985. Physiological effects of the MSX parasite Haplosporidium
nelsoni (Haskin, Stauber and Mackin) on the American oyster, Crassostrea
virginica. Journal of Shellfish Research. 5: 91-96.

218

Oyster Biology and Culture in India

Newell, I.E. and C.J. Langdon. 1996. General Anatomy. Pages 185-223 In: V.S.
Kennedy, R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster Crassostrea
virginica, published by the Maryland Sea Grant College, University of Maryland
System, College Park.

Newkirk, G.F. 1980. Review of the genetics and potential for selective breeding of
commercially important bivalves. Aquaculture 19: 209-228.

Newkirk, G.F. 1988. Response to selection for growth in Ostrea edulis : second
generation. Journal of Shellfish Research. 7: 172 (abstract).

Newkirk,G.F. 1991 . The world of oyster culture: focus on Asia. INF OFISH International.
6/91: 43-46.

Newkirk, G.F. 1996. Culture: Genetic improvement. Pages 661-690 in V.S. Kennedy,
R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster , Crassostrea virginica,
Maryland Sea Grant College Publication.

Newkirk, G.F., L.E. Haley, D.L. Waugh and R. Doyle. 1977. Genetics of larvae and
spat growth rate in the oyster Crassostrea virginica. Marine Biology. 41: 49-52.

Newkirk, G.F. and L.E. Haley. 1983. Selection for growth rate in the European oyster
Ostrea edulis : response of second generation groups. Aquaculture. 33: 149-155.

Nishihama, Y., H. Takashi, M. Satoshi and Y. Shuichi. 1998. Effect of oil pollution and
its recovery on the activity and taste of the bivalve Pseudocardium sachalinensis
caused by an oil spill accident off Tomakomai, Hokkaido. Scientific Reports of
Hokkaido Fisheries Experimental Station. 53: 17-24.

Nugranad, J. 1991. Mollusc hatchery in Thailand: Prachuap Khiri Khan hatchery
experience. Phuket Marine Biological Special Publication. 9: 79-81.

Numachi, K., J. Oizumi, S. Sato and T. Imai. 1965. Studies on the mass mortality of
the oyster in Mstsushima Bay. III. The pathological changes of the oyster caused
by gram positive bacteria and frequency of their infection. Tohoku-ku Suisan
Kenkyusho Kenkyu Kokoku 25: 39-48 (in Japanese, English summary).

Numaguchi, K and J.A. Nell. 1991. Effects of gelatin-acacia microcapsule and algal
meal supplementation of algal diets on growth rates of Sydney rock oyster
Saccostrea commercialis (Iredale and Roughley)larvae. Aquaculture. 94 : 65-78.

Onishi, T., M. Suzuki and R. Kikuchi. 1985. The distribution of polysaccharide
hydrolase in gastropods and bivalves. Bulletin of Japanese Society of Scientific
Fisheries. 51: 301-308.

Onoue, Y., T. Noguchi and K. Hashimoto. 1980. Studies on paralytic shellfish poison
from the oyster cultured in Senzaki Bay, Yamaguchi Prefecture. Bulletin of the
Japanese Society of Scientific Fisheries. 46: 1031-1034.

Owen, G. 1974. Studies on the gill of Mytilus edulis. The eulatero-frontal cirri.
Proceedings of Research Society of London B. 187: 83-91.

Owen, H.M. 1953. The relationship of high temperatures and low rainfall to oyster
production in Louisiana. Bulletin of Marine Sciences. 3: 34-43.

Palaniswamy, R. and S.M. Sathakkathullah. 1992. Holding and spawning of the edible
oyster, Crassostrea madrasensis during off season. Mar. Fish. Inf or. Serv., T&E
Ser, No. 118: 13.

Palaniswamy, R. and M.E.Rajapandian. 1997. On the microalgal species as feed for
conditioning adult oyster, Crassostrea madrasensis (Preston). Journal of Marine
Biological Association of India. 39(1&2): 159-162.

References

219

Palmer, R.E. and L.G. Williams. 1980. Effect of particle concentration on filtration
efficiency of the bay scallop Argopecten irradians and the oyster Crassostrea
virginica. Ophelia 19: 163-174.

Panikkar, N.K. and Aiyar, R.G. 1939. Observations on breeding in brackishwater
animals of Madras. Proceedings of Indian Academy of Science Sectariat. B. 9:
343-364.

Patterson, J and K. Ayyakkannu. 1 997. Spat settlement and growth of the edible oyster,
Crassostrea madrasensis (Preston) in the Vellar estuary, Parangipettai, India.
Phuket Marine Biological Center Special Publication 17(1): 263-268.

Paul, M.D. 1942. Studies on the growth and breeding of certain sedentary organisms
in the Madras Harbour. Proceedings of Indian Academy of Science Sectariat. B,
15: 1-42.

Paynter, K.T. and L. Dimichele. 1990. Growth of tray cultured oysters ( Crassostrea
virginica, Gmelin) in Chesapeake Bay. Aquaculture 87: 289-291.

Paynter, K.T., S.K. Pierce and E.M. Burreson. 1995. Levels of intracellular free amino
acids used for salinity tolerance by oyster ( Crassostrea virginica ) are altered by
protozoan ( Perkinsus marinus) parasitism. Marine Biology. 122: 61-12.

Perdue, J.A., J.H. Beattie and K.K. Chew. 1981. Some relationships between
gametogenic cycle and summer mortality phenomenon in the Pacific oyster
( Crassostrea gigas) in Washington state. Journal of Shellfish Research. 1:9-16.

Perkins, F.O. 1988. Structure of protistan parasites found in bivalve molluscs. Pages
93-111 in W.S. Fisher (Eds.), Disease Processes in Marine Bivalve Molluscs.
Amer. Fish. Soc. Spec. Publ. 18. Bethesda, Maryland.

Perkins, F.O. 1993. Infectious diseases of Molluscs. Pages 255-285 in J.A. Couch and
J.W. Foumie (Eds.), Pathobiology of Marine and Estuarine organisms. CRC
Press, Boca Raton Florida.

Perkins, F.O. and P.H. Wolf. 1976. Fine structure of Marteilia sydneyi sp.n -
haplosporidian pathogen of Australian oysters. Journal of Parasitology. 62:
528-538.

Pillai., K.V. and K. Selvan. 1988. Study on the bacterial quality of edible oyster
Crassostrea madarensis and its purification. Bulletin of Central Marine Fisheries
Research Institute. 42 (2): 426 - 431.

Pillai, V.K., A.G. Ponniah, K.K. Valsala and P.V.R. Nair. 1986. Heavy metal load in
a few bivalves from the coastal waters of South India. In: Proceedings of the
National Seminar on Mussel watch 13-14 February, 1986. Sponsored by the
University of Cochin, 93-104.

Pillay. , T.V.R. 1990. Aquaculture : Principles and Practices. Fishing News Books Ltd.
576 pp.

Poder, M., A. Cahour and G. Balouet. 1982. Hemocytic parasitosis in European oyster
Ostrea edulis L.: Pathology and contamination. Pro. Int. Colloq. Invertebr.
Pathol. 3rd pp. 254-257.

Poisson, H. 1946. Huitres et ostreiculture a Madagascar. Etude zoologique et
economique. Trav. Sect. Oceanogr. Appl. Soc. Amis Parc Botan. Zool. Tananariva,
3:1-37.

Preston, H.B. 1916. Report on a collection of Mollusca from Cochin backwaters.
Records of Indian Museum, 12: 27-39

220

Oyster Biology and Culture in India

Pripanapong, S. and K. Youngvanichset. 2000. Current status of oyster Crassostrea
belcheri (Soweiby). Mollusk Research in Asia. 137-139.

Purushan, K.S, U.K. Gopalan and T.S.S. Rao. 1983. On the setting of spat and growth
of the edible oyster Crassostrea madrasensis (Preston) in Cochin backwater.
Proceedings of Symposia. Coastal Aquaculture 2: 444-450.

Quayle, D.B. and G.F. Newkirk. 1989. Farming bivalve molluscs: Methods for study
and development. Advances in World Aquaculture, Volume 1. Published by the
World Aquaculture Society. CA, USA: 194 pp.

Raghukumar, C and V. Lande. 1988. Shell disease of rock oyster Crassostrea cucullata.
Dis. Aquat. Org. 4: 77-81.

Rai, H.S. 1928. A short account of the oyster industry in the islands of Bombay and
Salsette. Journal of Bombay Natural History Society., 33: 893-898.

Rai, H.S. 1932. The shell fisheries of the Bombay Presidency. Journal of Bombay
Natural History Society. 35 (4): 826-847.

Rajapandian, M.E. and C.T. Rajan. 1983. Studies on maturity stages and spawning
periodicity of Crassostrea madrasensis (Preston) atTutricorin Bay. Proceedings
of Symposia. Coastal Aquaculture, 2:475-478.

Rajapandian, M.E. and C.T. Rajan. 1987. Biological aspects of oysters. Bulletin of
Central Marine Fisheries Research Institute., 38: 30-40.

Rajapandian, M.E., K.S. Rao, P. Muthiah and D. Sundararajan. 1988. Post harvest
techniques and sanitation for oysters. Bulletin of Central Marine Fisheries
Research Institute. 42(2): 394-397.

Rajapandian, M.E., K. Ramadoss, D. Sundararajan, S.M. Sathakathullah and R.
Athipandian. 1993. Experience paper on the operation of pilot project on oyster
culture at Tuticorin. Mar. Fish. Infor. Serv., T&E Ser., No. 125: 3-7.

Rajesh, K. V., K. S. Mohamed, and V. Kripa. 2001. Influence of algal cell concentration,
salinity and body size on the filtration and ingestion rates of cultivable Indian
bivalves. Indian Journal of Marine Sciences., 30(2):87-92.

Ramachandran, N. 1988. Oyster resources of Karwar. Bulletin of Central Marine
Fisheries Research Institute., 42(1): 236-238.

Ramakrishna, K. V. 1 988. Development of oyster culture in Pulicat Lake area- prospects
and problems. Bulletin of Central Marine Fisheries Research Institute., 42(2):
275-281.

Rao, G.S., K.R. Somayajalu and P. Achayya. 1994. Prospects for developingculture of
edible oyster, Crassostrea madrasensis and green mussel, Perna virdis along
Kakinada coast, Andhra Pradesh. Mar. Fish Infor.Ser. T&E Ser., No. 135: 1-5.

Rao, K.S. 1974. Edible bivalves: mussels and oysters. In: Commercial Molluscs of
India. Bulletin of Central Marine Fisheries Research Institute, 25: 4-39.

Rao, K.S. 1987. Taxonomy of Indian oysters. Bulletin of Central Marine Fisheries
Research Institute, 38: 59-62.

Rao, K.S., and K.S. Sundaram, 1972. Ecology of intertidal molluscs of Gulf of Mannar
and Palk Bay. Proceeding of Indian National Science Academy., 38: 462-474.

Rao, K.S., D. Sivalingam and K.A. Unnithan. 1983. Observations on the setting of
spat and growth of Crassostrea madrasensis in Vaigai estuary, Athankarai.
Proceedings of Symposium on Coastal Aquaculture, 2: 436-443.

References

221

Rao, K.S., D.Sivalingam, RN.R. Nair and K.A. Unnithan. 1987. Oyster resources of
Athankarai estuary, South-west of India. Bulletin of Central Marine Fisheries
Research Institute, 38: 17-29.

Rao, K.S., M.E. Rajapandian, P. Muthiah, Rani Palaniswamy, K. Ramadoss and

C.P. Gopinathan. 1992. The Indian edible oyster. Technology of seed production and
farming. CMFRI Publication. 23 pp.

Rao, K.S., P.V. Sreenivasan, P. Muthiah, R. Sarvesan, P. Natarajan, M.E. Rajapandian,
C.T. Rajan, R. Thangavelu, D. Sundararajan and P. Poovannan, 1996. Distribution
and exploitation of oyster resources along the south-east and south-west coasts
of India. Mar. Fish. Infor. Serv., T&E Ser., No. 145: 1-16.

Rao, K.V. 1951. Observations on the probable effects of salinity on the spawning,
development and setting of the Indian backwater oyster Ostrea madrasensis
Preston. Proceedings of Indian Academy of Sciences., 33B: 233-256.

Rao, K.V. 1953. Sex change in the oviparous Indian backwater oyster, Ostrea
madrasensis Preston. Current Science., 22: 377-378.

Rao, K.V. 1956. Seasonal gonadal changes in the adult backwater oyster Ostrea
(Crassostrea) madrasensis (Preston) from Ennur near Madras. Proceeding of
Indian Academy of Sciences., 144B: 332-356.

Rao, K.V. 1958. Molluscan fisheries. Pages 55-59 in S.Jones (Ed.), Fisheries of West
coast of India: 55-59.

Rao, K.V. 1 963. Edible molluscan shell-fish of India. Indian Fish Bulletin., 10(3): 23-27.

Rao, K.V. 1966. Oysters, Wealth of India-Raw Materials, Council of Scientific and
Industrial Research, New Delhi, 7:202-207.

Rao, K.V. 1983. Induced aspawning of the adults and laboratory rearing of the larvae
of the edible oyster Crassostrea madrasensis (Preston). Proceeding of Symposium.
Coastal Aquaculture Marine Biological Association India. 2: 479-482.

Rao, K.V. and K.N. Nayar. 1956. Rate of growth in spat and yearlings of the Indian
backwater oyster Ostrea madrasensis (Preston). Indian Journal of Fisheries.,
30: 231-260.

Ray, S.M., J.G. Mackin and J.L. Boswell, 1953. Quantitative measurement of the
effect on oysters of disease caused by Dermocystidium marinum. Bull. Mar. Sci.
Gulf and Carib., 3 : 6-33.

Ray, S.M. and K.S. Rao. 1984. Manual on marine toxins in bivalve molluscs and
general consideration of shellfish sanitation. Central Marine Fisheries Research
Institute., Spl.publ.16 : 99pp.

Renard, P. 1991. Cooling and freezing embryos of the Pacific oyster Crassostrea
gigas: methanol and sucrose effects. Aquaculture, 92: 43-57.

Reuben S., T.A. Rao and P.E.S. Manickam 1983. Culture experiments on the edible
oyster Crassostrea madrasensis in the Bheemunipatnam backwater. Proceedings
of the Symposium Coastal Aquaculture, 2: 456-459

Riquelme, C., G. Hayashida, R. Araya, A. Uchida, M. Satomi and Y. Ishida. 1996.
Isolation of a native bacterial strain from the scallop Argopecten purpuratus
with inhibitory effects against pathogenic vibrios. Journal of Shellfish Research.,
15(2): 369-374.

Riquelme, C., R. Araya, N. Vergara, A. Rojas, M. Guaita and M. Candia. 1997.
Potential probiotic strains in the culture of the Chilean scallop Argopecten
purpuratus (Lamarck, 1819). Aquaculture, \S^X: 17-26.

222

Oyster Biology and Culture in India

Ritter, D. F. 1986. Process of geomorphology, second edition, Wm. C. Brown, Dunuque,
Iowa.

Riisgard, H.U. 1988. Efficiency of particle retention and filtration rate in 6 species of
northeast American bivalves. Mar. Ecol. Prog. Ser. 45:217-223.

Robertson, R. 1978. Spermatophores of six eastern North American Pyramidellid
gastropods and their systematic significance (with the new genus Borneo).
Biological Bulletin. 155: 360-382.

Roche, G.R. and E.M. Lafon. 1951. Sur la composition des scleroproteines des
coquilles des mollusques (conchiolines). Pages 1474-1477 in Comptes Rendus
des Seances de la Societe de Biologie et de ses Filiales, tome.

Rogan, E. 1994. Frozen gene banks. Aquaculture Ireland. March : 25-28.

Roland, W.G., T.A. Broadley and I.R. Sutherland. 1989. Solving problems with
remote setting Pacific oyster larvae in British Columbia. Journal of Shellfish
Research., 8: 324.

Romalde, J.L., A.E. Toranzo and J.l. Barja. 1990. Changes in bacterial populations
during red tides caused by Mesodinium rubrum and Gymnodinium catenatum
in North West coast of Spain. Journal of Applied Bacteriology., 68: 123-132.

Rothschild, B.J., J.S. Auct, P. Goulletquer and M. Heral. 1994. Decline of the
Chesapeake Bay oyster population: a century of habitat destruction and
overfishing. Mar. Ecol. Prog. Ser., 3: 29-39.

Ruiz, C., Martinez, D.G. Mosquera, M. Abad, and J.L. Sanchez. 1992. Seasonal
variations in condition, reproductive activity and biochemical composition of
the flat oyster Ostrea e dulls, from San Cibran (Galicia, Spain), Marine Biology.,
112(1): 67-74.

Ruwa, R.K. 1990. Growth of Crassostrea cucullata Bom (Bivalvia) at different levels
in the intertidal zone. Aquaculture, 88: 303-312.

Samuel, D. 1976. A digenic trematode infection in the edible oyster Crassostrea
madrasensis (Preston). Indian Journal of Fisheries., 23(1 &2): 153-159.

Samuel, D. 1983. Early larval development of edible oyster Crassostrea madrasensis
(Preston). Proceedings of the Symposium Coastal Aquaculture, 2: 483-487.

Sankaranarayanan, V.N., K.S. Purushan and T.S.S. Rao. 1978. Concentration of some
of the heavy metals in the oyster, Crassostrea madrasensis (Preston), from the
Cochin region. Indian Journal of Marine Sciences., 7: 130-131.

Saraya, A. 1982. Country report-Thailand. In: Bivalve culture in Asia and the Pacific
(Ed.) F.B.Davy and M. Graham. IDRC-200e; Canada: pp. 73-78.

Sarvesan, R., R. Thangavelu, P.V. Sreenivasan, K.S. Sundaram and P. Poovannan.
1988. Edible oyster resources of Ennore estuary and Muttukadu backwater,
Madras. Bulletin of Central Marine Fisheries Research Institute., 42(l):50-58.

Sarvesan, R., P.V. Sreenivasan, K.S. Rao, R. Thangavelu and P. Poovannan, 1990.
Reproductive biology and setting of spat of Crassostrea madrasensis (Preston)
in Muttukadu backwater. Journal of Marine Biological Association of India, 32
(1&2): 119-128.

Satyamurthi, S.T. 1956. The Mollusca of Krusadai Island (in Gulf of Mannar) II.
Scaphopoda, Pelecypoda and Cephalopoda. Bull. Madras Govt. Mus. (New
Ser). Nat. Hist. Sect., 1 (2) pt. 7. 202pp.

References

223

Scarpa, J. and S.K. Allen., Jr. 1992. Comparative kinetics of meiosis and hybrid
crosses of Crassostrea gigas and C. rivularis with C. virginica. Journal of
Experimental Zoology., 263: 316-322.

Scarpa, J., J.E. Toro and K.T. Wada. 1994. Direct comparison of six methods to induce
triploidy in bivalves. Aquaculture, 119: 119-133.

Schlauch, J. 1999. Development and structure of the German mollusc fishery and
culture in the trilateral comparison with Denmark and the Netherlands. Bamb-
Wirtschaftsgeogr-Arb (Abstract).

Schlicht, F.G. and J.G. Mackin. 1968. Hexamita nelsoni sp. n. (Polymastigina:
Hexamitidae) parasitic in oysters. Journal of Invertebrate Pathology., 11: 35-39.

Scott, G.I. and D.P. Middaugh. 1978. Seasonal chronic toxicity of chlorination to the
American oyster, Crassostrea virginica, Pages 31 1-328. in Ann Arbor Science
Publ. Inc., Water chlorination: Vol 2, Environmental Impact and Health Effects
Ann Arbor, Michigan.

Scott, G.I., and W.B. Vernberg, 1979. Co-occuring chlorine produced oxidants in
seawater and their effect on the growth, survival, and physiology of the American
oyster, Crassostrea virginica (Gmelin). Evidence for synergistic effects with
seasonal temperature stress, pages 415-435. In: W.B. Vernberg, F. Thurberg, A.
Calabreese, and F.J. Vernberg (Eds.), Marine Pollution: Functional Responses.
Academic Press, New York.

Scott, G.I. and D.R. Lawrence. 1982. The American oyster as a coastal zone pollution
monitor: A pilot study. Estuaries, 5:27-33.

Shaw. B.L and H.I. Battle. 1957. The gross and microscopic anatomy of the digestive
tract of the oyster. Crassostrea virginica (Gmelin). Canadian Journal of Zoology.,
35: 325-347.

Sheridan, A.K. 1981. Cross breeding and heterosis. Animal Breeding Abstracts, 49:
131-144.

Sheridan, A.K. 1997. Genetic improvement of oyster production - a critique.
Aquaculture, 153: 165-179.

Sheridan, A.K., I.R. Smith and J.A. Nell. 1996. Reducing the impact of environmental
variation in a growth rate improvement programme for the Sydney rock oyster
Saccostrea commercialis. Canadian Journal of Genetics and Cytology., 23:
119-130.

Shilu, L. and H.Linhua. 2002. Mariculture in China. INFOFISH International, 1/
2002: 33-38.

Shpigel, M., J. Lee, B. Soohoo, R. Fridman and H. Gordin. 1993. Use of water from
fish ponds as a food source of the Pacific oyster, Crassostrea gigas Thunberg.
Aquaculture and Fisheries Management, 24: 529-543.

Shumway, S.E. 1990. A review of the effects of algal blooms on shellfish and
aquaculture. Journal of World Aquaculture Society., 22(2): 65-104.

Shumway, S.E. 1996. Natural environmental factors. In: V.S. Kennedy, R.I.E. Newell
and A.F. Eble (Eds.), The Eastern oyster Crassostrea virginica, published by the
Maryland Sea Grant College, University of Maryland System, College Park:
467-503.

Siddal, M.E., N.A. Stokes and E.M. Burreson. 1995. Molecular phylogenetic evidence
that the phylum Haplosporidia has an alveolate ancestry. Molecular Biology
Evolution, 12: 573-581.

224

Oyster Biology and Culture in India

Silas, E.G., K. Alagarswami, K.A. Narasimham, K.K. Appukuttan and P. Muthiah.
1982. Country report- India. Pages 34-41 in F.B.Davy and M. Graham (Eds.),
Bivalve culture in Asia and the Pacific. Proceedings of a workshop held at
Singapore, 16-19 February, 1982. International Development Research Centre-
200e, Canada.

Simkiss, K and K.M. Wilbur. 1989. Biomineralization , Cell Biology and Mineral
Deposition. Academic Press, New York. 337 pp.

Sindermann, C.J. 1968a. Oyster mortalities, with particular reference to Chesapeake
Bay and Atlantic coast of North America. U.S. Fish Wildlife Services , Sepcial
Science Report-Fisheries, 569:10pp.

Sindermann, C.J. 1968b. Bibliography of oyster parasites and diseases. U.S. Fish
Wildlife Services, Sepcial Science Report-Fisheries, 563: 13pp.

Sindermann, C.J. 1990. Shellfish diseases of public health significance. In: Principal
Diseases of Marine Fish and Shellfish, Vol.2. Academic Press Limited: 516pp.

Sindermann, C.J. and D.V. Lightner. 1988. Disease diagnosis and control in North
American Marine Aquaculture, Elsevier, New York. 431 pp.

Singh, S.M. and E. Zouros.1981. Genetics of growth rate in oysters and its implications
for aquaculture. Canadian Journal of Genetics and Cytology., 23: 119-130.

Smith, J.W. and J.V. Merriner. 1978. Biology and identification of rays in the Chesapeake
Bay. Virginia Institute of Marine Science. Educ. Ser., 20, Gloucester Point, 22

pp.

Smith, P.J., H. Ozaki and Y. Fugio. 1986. No evidence for reduced genetic variation
in the accidentally introduced oyster Crassostrea gigas in New Zealand. N.Z. J.
Mar. Freshwater Research., 20: 569-574.

Smith, R.A. and E.R. Wright. 1962. Elemental composition of oyster shell. Texas
Journal of Science, 14(2): 222-224.

Smith, J.C., R. Cormier, J. Worms, C.J. Bird, R. Pocklington, R. Angus and L. Hanic,
1990. Toxic blooms of the domoic acid containing diatom Nitzschia pungens in
the Cardigan River, Prince Edward Island, in 1988. pages 227-232 in E.Granete,
D.M. Andersen, L.Edler and B.G. Sundstrom (Eds). Toxic Marine Phytoplankton.
Elsevier, New York, USA.

Soletchnik, P., A. Huvet, O.L. Moine, D. Razet, P. Geairon, N. Faury, P. Goulletquer
and P. Boudry. 2002. A comparative field study of growth, survival and
reproduction of Crassostrea gigas, C. angulata and their hybrids. Acquatic
Living Resources, 15(4): 243-250.

Somasekar, M, K. Sriraman and R. Kasinathan. 1982. Age, growth and length-weight
relationship in backwater oyster Crassostrea madrasensis (Preston). Indian
Journal of Marine Sciences., 11: 190-192.

Soniat, T.M. and M.L. Kaenig. 1982. The effects of parasitism by Perkinsus marinus
on the free aminoacid composition of Crassostrea virginica mantle tissue.
Journal of Shellfish Research., 2: 25-28.

Sournia, A. 197 1 . Phytoplankton manual. Monograph on Oceanographic methodology.
UNESCO, 6: 1-337.

Sournia, A., M.J. Chretiennot-Dinet and M. Richard. 1991. Marine phytoplankton:
how many species in the world ocean?- Journal of Plankton Research. 13:
1093-1099.

References

225

Sparks, A.K. 1962. Metaplasia of the gut of the oyster Crassostrea gigas (Thunberg)
caused by infection with the copepod Mytilicola orientalis Mori. Journal of
Insect Pathology., 4:57-62.

Sparks, A.K. 1985. Synopsis of Invertebrate Pathology. Elsevier, New York, 423 pp.

Spencer, B.E., M.J. Akester and I. Mayer. 1986. Growth and survival of seed oysters
in outdoor pumped upwelling systems supplied with fertilised seawater.
Aquaculture, 55: 173-189.

Spencer, B.E. 1990. Cultivation of Pacific oysters. Lab. Laefl., MAFF Direct Fish.
Res. Lowestoff 63: 47 pp.

Sprague, V. 1964. Nosema dollfusi n. sp. (Microsporidia, Nosmatidae), a hyperparasite
of Bucephalus cuculus in Crassostrea virginica. Journal of Protozoology.,
11:381-385.

Sprague, V. 1970. Some protozoan parasites and hyperparasites in marine bivalve
molluscs. Pages 51 1-526 in S.F. Snieszko (Eds.), A Symposium on diseases of
Fishes and Shellfishes. Amer. Fish. Soc. Spec. Publ., 5, Washington DC.

Sreenivasan,P.V., R.Thangavelu and P.Poovannan 1996. Coleroon estuary, Tamil Nadu
- A potential area for edible oyster and green mussel culture. Mar.Fish Infor.
Serv.T&E Ser.142 : 11-13.

Stanley, J.G. and M.A. Sellers. 1986. American Oysters. Species profiles: Life histories
and environmental requirements of coastal fishes and invertebrates (Mid Atlantic).
Biological Report, 82 (1 1 .65). TR EL- 28-4. Department Interior, of Washington.
D.C.

Stanley, J.G., S.K. Allen., Jr. and H. Hidu. 1981. Polyploidy induced in the American
oyster, Crassostrea virginica, with cytochalasin B. Aquaculture, 23: 1-10.

Stauber, L.A. 1945. Pinnotheres ostreum, parasite of the American oyster, Ostrea
(Gryphaea) virginica. Biological Bulletin., (Woods Hole, Mass.) 88: 269-291.

Steinberg, P.D. and V.S. Kennedy. 1979. Predation upon Crassostrea virginica larvae
by two invertebrate species common in Chesapeake Bay oyster bars. Veliger, 22:
78-84.

Stenzel, H.B. 1971. Oysters. In Treatise on Invertebrate Paleontology. Mollusca 6.
K.C. Moore (Eds.), Geological Society of America and Univ. Kansas, Boulder,
Colardo. N:953 3(3): 924-1224.

Stephen, D. 1977. Parasitic castration of the Indian backwater oyster Crassostrea
madrasensis (Preston) by the larval trematode Bucephalus sp. Sci. Cult.,
43:387-388.

Stephen, D. 1978. Mudblister formation by Polydora ciliata in the Indian backwater
oyster Crassostrea madrasensis (Preston), Aquaculture, 13:347-350.

Stephen, D. 1980. The reproductive biology of the Indian oyster Crassostrea
madrasensis. 2. Gametogenic pattern and salinity. Aquaculture, 21(2): 139-149.

Stiles, S.S. 1978. Conventional and experimental approaches to hybridization and
inbreeding research in the oysters. Proceedings of World Marine Society., 9:
577-586.

Subramanyam, N. and R. Gopalakrishnan. 2000. Composite farming of the green
mussel, Perna viridis with the shrimp Penaeus monodon along the Okhamandal
coast of Arabian sea in Gujarat. Fishery Technology, 37(1): 55-58.

226

Oyster Biology and Culture in India

Summer, C.E. 1981. Growth of Pacific oyster, Crassostrea gigas Thunberg, cultivated
in Tasmania.II. Subtidal culture. Australian Journal of Marine and Freshwater
Research ., 32: 411-416.

Sundaram, K.S. 1988. Rock oyster resources of Bombay coast. Bulletin of Central
Marine Fisheries Research Institute., 42(l):29-35.

Sukumar, P. and M.M. Joseph. 1988. Annual reproductive cycle of Saccostrea cucculata
(von Born ) Pages 207-210 In M. Mohan Joseph (Ed.), Proc. First Indian
Fisheries Forum. Asian Fisheries Society, Indian branch, Mangalore.

Takatsuki, S. 1934. On the nature and functions of the amoebocytes of Ostrea edulis.
Quart. J. Microsc. Sci., 76:379-431.

Tall, B.D. and R.K. Nauman. 1981. Scanning electron microscopy of Cristispira
species in Chesapeake Bay oysters. Applied Environmental Microbiology .,
42:336-343.

Tannock, G.W. 1997. Modification of the normal microbiota by diet, stress, anti¬
microbial agents and probiotics. Pages 434-465. In Mackie, R.I., With, B.A.,
Isaacson , R.E. (Eds) Gastrointestinal Microbes and Host Interactions. Chapman
and Hall Microbiology Series, International Thomson Publishing, New York.

Thangavelu, R. 1988. Settlement of spat of the backwater oyster Crassostrea
madrasensis (Preston) in Pulicat Fake. Bulletin of Central Marine Fisheries
Research Institute., 42(2): 318-323.

Thangavelu, R and N. Sundaram. 1983. Experiments on edible oyster spat collection
at Tuticorin. Proceeding of the Symposium on Coastal Aquaculture, 2: 460-466.

Thangavelu, R., and P. Muthiah. 1983. Predation of oyster Crassostrea madrasensis
by gastropod Cymatium cingulatum (Famarck) in the oyster farm at Tuticorin.
Proceeding of Symposium Coastal Aquaculture. Marine Biological Association
India., 2: 488-494.

Thangavelu, R and P.J. Sanjeevaraj. 1985. Growth of the oyster Crassostrea madrasensis
(Preston) in the Pulicat Fake. Journal of Marine Biological Association of
India., 27(1&2): 84-87

Thangavelu, R and P.J. Sanjeevaraj. 1988a. Distribution of molluscan fauna in the
Pulicat Fake. Bulletin of Central Marine Fisheries Research Institute., 42(1):
58-67.

Thangavelu, R and P.J. Sanjeevaraj. 1988b. Boring and fouling organisms of the edible
oyster Crassostrea madrasensis (Preston) from Pulicat Fake. Journal of Marine
Biological Association of India., 30(1&2): 47-53.

Thangavelu, R and P.J. Sanjeevaraj. 1988c. Host parasitic relation between
Bucephalopsis haemeanas and Crassostrea madrasensis (Preston) in Pulicat
Fake. Journal of Marine Biological Association of India., 29(1&2): 220-231

Thiriot-Quievreux, C., G.H. Pogson and E. Zouros. 1992. Genetics of growth rate
variation in bivalves : aneuploidy and heterozygosity effects in a Crassostrea
family. Genome, 35: 39-45.

Thiriot-Quievreux, C., T. Niel, S. Bougrier and S. Dallot. 1988. Relationship between
aneuploidy and growth rate in pair matings of the oyster Crassostrea gigas.
Aquaculture, 75: 89-96.

Thomas, PA. 1979. Boring sponges destructive to economically important molluscan
beds and coral reefs in Indian seas. Indian Journal of Fisheries., 26 ( 1&2): 163-
200.

References

227

Thomas, P. A., K.Ramadoss and S.G. Vincent. 1993. Invasion of Cliona margaratifera
Dendy and C.lobata Hancoak on the molluscan beds of the Indian coast.
Journal of Biological Boilogy Association of India., 35 (122) : 145 -156.

Thompson, G. T and T.J. Chow. 1955. The strontium-calcium atom ratio in carbonate
secreting marine organisms. Deep Sea Research, 3: 20-30.

Thompson, R.J., R.I.E. Newell, V.S. Kennedy and Roger Mann. 1996. General Anatomy.
Pages 335-364 in V.S. Kennedy, R.I.E. Newell and A.F. Eble (Eds.), The
Eastern oyster Crassostrea virginica, published by the Maryland Sea Grant
College, University of Maryland System, College Park.

Thomson, J.M. 1954. The genera of oysters and the Australian species. Australian
Journal of Marine Freshwater Research., 5: 132-168.

Thrower, S.J. 1990. Shellfish depuration. INFOFISH International, 5/90: 48-51.

Tiensongrasmee, B. 2000. An overview of oyster culture in Thailand. In: B.
Tiensongrasmee et.al. (Ed.) Mollusc Research in Asia. (Abstract).

Tookwinas, S., Y. Kunvasu, S.Thipyothin, C. Mangkolmad, W. Kumsupha and
W.Warasayan, 1990. Investigation on the cause of oyster mass mortality at Bang
Prong Bay, Chonburi Province. Technical paper No. 10/1990. Subdivision of
Coastal Zone Management for Aquaculture, Coastal Aquaculture Division,
Department of Fisheries, Thailand.

Torigoe, K. 1981. Oysters in Japan. J. Sci. Hiroshima Univ., Ser. B, Div. 1 ( Zool .),
29:291-319.

Toro, J.E. and G.F. Newkirk. 1990. Divergent selection for growth rate in the European
oyster Ostrea edulis: response to selection and estimation of genetic parameters.
Mar. Ecol. Progr. Ser., 62: 219-227.

Tritar, S., D. Prieur and R. Weiner. 1992. Effects of bacterial films on the settlements
of the oysters, Crassostrea gigas (Thunberg, 1793), and Ostrea edulis (Linnaeus,
1750) and the scallop Pecten maximus (Linnaeus, 1758). Journal of Shellfish
Research., 11: 325-330.

Tubiash, H.S. 1975. Bacterial pathogens associated with cultured bivalve mollusk
larvae. Pages 61-71 . In W.L. Smith and M.H. Chanley (Eds.), Culture of Marine
Invertebrate Animals, Plenum, New York.

Tubiash, H.S., P.E. Chanley and E. Leifson. 1965. Bacillary necrosis, a disease of
larval and juvenile bivalve mollusks. Ethiology and epizootiology. Journal of
Bacteriology., 1036-1044.

Tubiash, H.S., R.R. Colwell and R. Sakazaki. 1970. Marine vibrios associated with
bacillary necrosis, a disease of larval and juvenile bivalve mollusks. Journal of
Bacteriology., 103: 272-273.

Tubiash, H.S., S.V. Otto and R. Hugh. 1973. Cardiac edema associated with Vibrio
anguillarium in the American oyster. Proceedings of National Shellfish
Association., 63: 39-42.

Turgeon, K.W. and D.S. Haven. 1978. Effects of corn-starch and dextrose in oysters.
Veliger, 20: 352-358.

Unnikrishnan, U., V. Kripa, K.S. Mohamed andT.S. Velayudhan. 2001. Studies on the
remote setting of two commercially important bivalves. Pages 343-356 in N.G.
Menon and P.P. Pillai (ed.) Perspectives in Mariculture, The Marine Biological
Association of India, Cochin: 343-356.

228

Oyster Biology and Culture in India

Urban, E.R. and C.J. Langdon. 1984. Reduction in costs of diets for the American
oyster, Crassostrea virginica (Gmelin) by the use of non-algal supplements.
Aquaculture , 38: 277-291.

Utting, S.D. 1993. Procedures for the maintenance and hatchery-conditioning ol
bivalve broodstocks. World Aquaculture, 24(3): 78-82.

Utting, S.D. and P.F. Millican. 1997. Techniques for the hatchery conditioning of
bivalve broodstocks and the subsequent effect on egg quality and larval viability.
Aquaculture, 155: 45-54.

Utting, S.D., B.E. Spencer. 1991. The hatchery culture of bivalve mollusc larvae and
juveniles. Laboratory Leaflet Number 68 MAFF Fish Research Lowestoft. 3 1 pp.
van Banning, P. 1982. Some aspects of the occurrence, importance and control of the
oyster pathogen Bonamia in a Dutch oyster culture. Proc. Int. Colloq. Invertebr.
Pathol., 3rd pp. 261-263.

van Banning, P. 1985. Control of Bonamia in Dutch oyster culture. Pages 393-396 in
A.E. Ellis, (ed.) Fish and Shellfish Pathology. Academic press, London.
Venkataraman, R. and T.Chari. 1951. Studies on oysters and clams. Biochemical
variations. Ind.J.Med.Res. 39 : 533 -541

Velayudhan, T.S., V. Kripa and K.A. Narasimham, 1995. Experimental culture of the
Indian oyster Crassostrea madrasensis (Preston) at Ashtamudi Lake, Kerala.
Seafood Export Journal, 26(8): 5-14.

Velayudhan, T.S., V. Kripa and K.K. Appukuttan. 1998. Production and economics of
edible oyster cultured in an estuarine system of Kerala. Mar. Fish. Infor. Serv.
T&ESer., No.154: 1-5.

Velayudhan T.S, V. Kripa, K.K. Appukuttan, K.S. Mohamed and P. Laxmilatha
(2000). Feasibility of integrated bivalve farming in an estuarine system of
Central Kerala, India. Pages 209-215. In B. Tiensongrasmee et.al. (ed.) Mollusk
Research in Asia.

Vrijenhoek, R.C., S.E. Ford and H.H. Haskin. 1990. Maintenance of heterozygosity
during selective breeding of oysters for resistance to MSX disease. J. Flerad.,
81: 418-423.

Walne, PR. 1956. Experimental rearing of larvae of Ostrea edulis L. in the laboratory.
Fish. Invest. Lond. Ser., II, 20, 1-23.

Walne, P.R. 1970. The seasonal variation of meat and glycogen content of seven
populations of oysters Ostrea edulis L. and a review of the literature. Min.
Agric. Fish. Food. Fish. Invest. Ser., 2. 26(3).

Walne, P.R. 1972. The influence of current speed, body size and water temperature on
the filtration rate of five species of bivalves. Journal of Marine Biological
Association. U.K., 52: 345-374.

Walne, P.R. 1974. Culture of bivalve molluscs. Fishing News (Books) Ltd. Surrey. 173

pp.

Walne, P.R. and R. Mann. 1975. Growth and biochemical composition in Ostrea edulis
and Crassostrea gigas. Pages 587 -607 in Barnes, H (ed.), Proc. 9th Europ. Mar.
boil. Symp., Aberdeen Univ. Press.

Wang, Z., X. Guo, S.K. Allen Jr.and R. Wang. 1999. Aneuploid Pacific oyster
( Crassostrea gigas, Thunberg) as incidentals from triploid production.
Aquaculture, 173: 347-357.

References

229

Wanninayake, W.M.T.B., M.H. Hewavitharana, J.M.P.K. Jayasinghe and U. Edirisinghe.
1998. Oyster, Crassostrea madrasensis in controlling suspended solid loading
and chlorophyll concentration in effluent water of semi-intensive shrimp culture
system in Sri Lanka. Page 269 in B. Tiensongrasmee et.al. (ed.) Mollusk
Research in Asia. (Abstract).

Ward, J.E. and C.J. Langdon. 1986. Effects of the ectoparasite Boonea ( =Odostomia )
impressa (Say) (Gastropoda: Pyramidellidae) on the growth rate, filtration rate,
and valve movements of the host ( Crassostrea virginica ) (Gmelin). Journal of
Experimental Marine Biology and Ecology., 99:163-180.

Ward, J.E., R.I.E. Newell, R.J. Thompson and B.A. MacDonald. 1994. Endoscopic
observations of particle capture and transport in the eastern oyster Crassostrea
virginica Gmelin. Biological Bulletin., 186:221-240.

Ward, R.D., L.J. English, D.J. McGoldrick, G.B. Maguire, T.A. Nell and P.A. Thompson
2000. Genetic improvement of the Pacific oyster Crassostrea gigas (Thunberg)
in Australia. Aquaculture Research, 31: 35-44.

Warren, C.E. 1971. Biology and water pollution control. W.B. Saunders Co.
Philadelphia. 434pp.

Watabe, N. 1984. Shell. Pages 448-485 In J. Bereiter-Hahn, A.G. Matolsty and
K.S. Richards (eds.). Biology of the Integument, Vol. 1. Invertebrates.
Springerverlag, New York.

Watabe, N. 1988. Shell structure. Pages 69-104. In K. Wilbur (Ed.), The Mollusca, Vol.
II, Form and Function. Academic Press, New York.

Wei, M. and H.A.M. Van der Steen. 1991. Comparison of reciprocal recurrent selection
with pure line selection system in animal breeding (A review). Animal Breeding
Abstract., 59 : 281-298.

Weiner, R.M., A.K. Segall and R. Colwell. 1985. Characterisation of a marine bacterium
associated with Crassostrea virginica (the eastern oyster). Applied Environmental
Microbiology., 49: 83-90.

Weiner, R.M., M. Walch, M.P. Labare, D.B. Bonar and R.R. Colwell. 1989. Effect of
biofilms of the marine bacterium Alteromonas colwelliana (LST) on set of the
oyster Crassostrrea gigas (Thunberg, 1793) and C. virginica (Gmelin, 1791 ). J.
Shellfish Res., 8: 117-123.

Wells, W.F. 1926. A new chapter in shellfish culture. N.Y.St. Conserv. Comm.,
Fifteenth Ann. Rep. 36pp.

Wells, W.F. 1927. Report of the experimental shellfish station. N.Y.St. Conserv. Dep.
Rep. 16. 22pp.

White, M.E., E.N. Powell, S.M. Ray and E.A. Wilson. 1987. Host-to-host transmission
of Perkinsus marinus in oyster Crassostrea virginica population by the
ectoparasitic snail Boonea impressa (Pyramidellidae). Journal of Shellfish
Research., 6: 1-5.

White, W.E. and E.A. Wilson. 1996. Predators, pests and competitors.Pages 559-575.
In V.S. Kennedy, R.I.E. Newell and A.F. Eble (Eds.), The Eastern oyster
Crassostrea virginica, published by the Maryland Sea Grant College, University
of Maryland System, College Park.

Wilbur, K.M. and G.Owen.1964. Growth. Pages 211 -242 in Wilber, K.M. and
Yonge,C.M.(Eds) Physiology of Mollusca . Academic Press, New York.

230

Oyster Biology and Culture in India

Wilbur, K.M. 1976. Recent studies of invertebrate mineralization. Pages 79-108 in N.
Watabe and K.M. Wilbur (Eds.), The mechanisms of Mineralization in the
Invertebrates and Plants. University of South Carolina Press, Columbia.

Wilbur, K.M. and A.S.M. Saleuddin. 1983. Shell formation. Pages 235-287 in K.M.
Wilbur (Eds.), The Mollusca, Vol. 4, Physiology, Part 1. Academic Press, New
York.

Wildish, D.J. and D.D. Kristmanson. 1979. Tidal energy and subtidal macrobenthic
animals in estuaries. J. Fish. Res. Board Canada., 36:1197-1206.

Wilson, E.A., E.N. Powell, M.A. Craig, T.L. Wade and J.M. Brooks. 1990. The
distribution of Perkinsus marinus in Gulf Coast oysters: Its relationship with
temperature, reproduction, and pollutant body burden. Int. Revue Der Gesamten.
Hydrobiol., 75:533-550.

Winslow, F. 1882. Methods and results. Report of the oyster beds of the James River,
Virginia and of Tangier and Pocomoke sounds, Maryland and Virginia.
Government Printing Office, Washington, D.C

Winstead, J.T. 1997. A histological study of digestive tubules in intertidal and subtidal
oysters, Crassostrea virginica, collected at high and low tides. Journal of
Shellfish Research., 16(1): 314-315.

Winstead, J.T. and J.A. Couch. 1988. Enhancement of protozoan pathogen Perkinsus
marinus in oysters Crassostrea virginica exposed to the chemical carcinogen n-
nitrosodiethylamine (DENA). Dis. Aquat. Org., 5:205-213.

Wolf, P.H. 1972. Occurrence of haplosporidian in Sydney rock oysters ( Crassostrea
commercials from Moretan Bay, Queensland, Australia. J. Invert. Pathol.,
19:416-417.

Wong, T.M. 1994. Hatchery production of bivalve seeds in southeast Asia; State of the
art and future research directions. Phuket Mar. biol. Cent. Spec. Publ., 13: 71-
80.

Wright, L.D., R.A. Gammiseh, and R.J. Bryne. 1990. Hydraulic roughness and
mobility of three oyster-bed artificial substrate material. Journal of Coastal
Research,. 867-878.

Yamaguchi. 1994. Shell structure and behaviour related to cementation in oyster.
Marine Biology., 118: 89-100.

Yavari, V. 1994. Studies on influence of environmental parameters affecting the
biology of oyster Crassostrea madrasensis (Preston) Ph.D. Thesis. Cochin
University of Science and Technology. 200 pp.

Yonge, C.M. 1926. Structure and physiology of the organs of feeding and digestion in
Ostrea edulis. Journal of Marine Biological Association. U.K., 14: 295-386.

Yoosukh, W. and D. Teerapong. 1998. Living oysters in Thailand. Pages 363-370
Hylleberg. J. (Eds.), Proc. ninth workshop of the Tropical Marine Mollusc
Programme(TMMP), Indonesia.

Young, A. and E. Serna. 1982. Country Report-Philippines. Pages 55-68 in F.B. Davy
and M. Graham (Eds.) Bivalve culture in Asia and the Pacific. IDRC-200e,
Canada.

Zhong-Qing.N. 1982. Country Report-China. Pages 21-33 in F.B. Davy and M.
Graham (Ed.) Bivalve culture in Asia and the Pacific. IDRC-200e, Canada.

References

231

Zingde, M.D., S.Y.S. Ringbal, C.F. Moraes and C.V.G. Reddy. 1976. Arsenic, Copper,
Zinc and Manganese in the marine flora and fauna of coastal and estuarine
waters around Goa. Indian Journal of Marine Sciences., 5: 212-217.

Zouros, E. and A.L. Mallet. 1989. Genetic explanations of the growth/heterozygosity
correlation in marine mollusks. Pages 317-324 in J.S. Ryland (Ed.) European
Marine Biology, Symposium on reproduction, genetics and distribution of
marine organisms.

Zouros, E., Thiriot-Quievreux and G. Kotoulas. 1996. The negative correlation between
somatic aneuploidy and growth in the oyster Crassostrea gigas and implications
for the effects of induced polyploidization. Genetic Research., 68: 109-116.

Index

Access 115
Alectyronella 8
Algae 59,61
Anatomy 30
Aneuploidy 182
Annelida 60
Annelids 62
Artificial Diets 166
Ashtamudi Lake 121

Bacterial diseases 73
Bamboo Stick Culture 162
Biochemical Composition 57
Biology 190
Birds 65
Bivalves 60, 63
Bonamiasis 77
Borers 61

Bottom Culture 117, 154, 162
Bryozoa 60

Cement Pipe Culture 162
Cement Pole Culture 162
Chordata 61

Chromosomal Engineering 178
Circulatory system 36
Classification 6
Coelenterata 60
Cooking: 132
Crassostrea 6
Crassostrea plicatula 150
Crassostrea gigas 152
Crassostrea rivularis 151
Crustacea 6 1 , 64
Culture Media 108
Culture Methods 193

Culture Sites 192

Dendostrea 7
Density of oysters 15
Depuration 132
Dermo 75

Digestive gland disease 77
Digestive system 35
Diseases 70

Distribution of Oysters 10

Echinoderms 64
Ecology of Oyster Beds 19
Excretory system 37

Fecundity 45
Filtration rates 42
Fishes 65
Flat worms 63
Food availability 22
Foulers 59
Fouling 114

Gastropods 63
Genetics 174

Hanging Culture 158
Harvest 1 09
Hatchery Seed 190
Hatchery Spat 1 1 5
Hermaphroditism 45
Heterosis 176
Heterozygosity 176
Horizontal zonation 15

Index

233

Hyotissa 7

Image analysis 181

Inbreeding 176

Intertidal Bottom Culture 117

Juvenile oyster disease 74

Larval Rearing 103
Lopha 7

Manipulated Yeasts 168
Mantle 30
Mass Culture 109
Microbial Pollutants 129
Microencapsulated Diets 167
Microfluorometry 1 8 1
MSX disease 76
Muscular system 32

Natural Seed 190
Natural Spat 115
Natural Spat Collection 91
Nervous system 39

Ostrea 7
Oyster Reef 23

Parasites 67

pH 22

Planostrea 8

Pollution 114

Porifera 60

Predation 114

Predation and Fouling 114

Predators 63

Probiotics 173
Public Health 193

Quantitative Genetics 174

Rack Culture 117,154
Raft Culture 154
Remote Setting 170
Reproduction 44
Reproductive system 40
Respiratory system 34

Saccostrea 7
Sex change 45
Shell morphology 28
Sponges 62
SSO disease 76
Stake Culture 125
Striostrea 7

Subtidal Bottom Culture 117

Taxonomy 5
Tiostrea 7
Tray Culture 162
Triploidy induction 179
Turbidity 21
Tuticorin bay 120

Unwanted Species 59

Viral diseases 71

Water Quality 114

Yeast 167

. • •

■

-CT-iW '

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "Textbook of Oyster Biology and Culture in India"

See other formats