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LIBRARY OF THE
UNIVERSITY OF ILLINOIS
AT URBANA-CHAMPAIGN

no.66G - 99

SURVEY

THE LIFE HISTORY OF THE SLENDERHEAD DARTER,
PERCINA PHOXOCEPHALA,
IN THE EMBARRAS RIVER, ILLINOIS

Lawrence M. Page
Philip W. Smith

HR AAAARRBANY

ILLINOIS NATURAL HISTORY SURVEY
Biological Notes No. 74

Urbana, Illinois July, 1971

State of Illinois
Department of Registration and Education
NATURAL HISTORY SURVEY DIVISION

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of Percina phoxocephala
is shaded on the Illinois map.

-Distribution
The study area

1.-

Fig.

THE LIFE HISTORY OF THE SLENDERHEAD
DARTER, PERCINA PHOXOCEPHALA,
IN THE EMBARRAS RIVER, ILLINOIS

THE SLENDERHEAD DARTER, Percina phoxo-
cephala (Nelson), is the most widely distributed and
best known of the four species assigned to the subgenus
Swainia, which also includes P. squamata (Gilbert &
Swain 1887), a species with a small range centered in
eastern Tennessee; P. oxyrhyncha (Hubbs & Raney
1939), limited to West Virginia and Virgina; and P.
nasuta (Bailey 1941), occurring in northern Arkansas,
eastern Oklahoma, and southern Missouri.

Despite many references to the occurrence, relative
abundance, and habitat preferences of P. phoxocephala,
details of its life history are limited to observations made
in Iowa by Karr (1963) and in Illinois by Thomas
(1970). No published information is available on the
life histories of the other species of Swainia. Because
of the paucity of life-history data and the availability of
a large population of P. phoxocephala in the middle
Embarras River, a detailed study of the life history of
this darter was commenced in August 1967 in conjunc-
tion with a similar study of the dusky darter, P. sciera.
References to P. scicra in the following text are based on
the latter investigation (Page & Smith 1970).

The slenderhead darter was described by Edward
W. Nelson (1876:35) as Etheostoma phoxocephalum
from “the Illinois [River] and its tributaries.” The
species (cover illustration) is a medium-sized darter,
sexually mature individuals ranging from 40 to 80 mm
in standard length, with a slender body and an attenu-
ated snout. Its scales are small, the lateral-line count
ranging from 60 to 80 scales. Opercles and nape are
scaled; cheek squamation is variable. The breast of the
female is naked, except for one or two enlarged, strongly
ctenoid scales. The posterior half of the male’s breast
is scaled; the anterior half is naked. Dorsal spines num-
ber 11 or 12, soft dorsal rays 11-14. The anal fin has
two spines and eight or nine soft rays. The gill covers
are moderately conjoined.

The dorsum is light brown or straw color with darker
brown vermiculations and blotches. The venter is white.
Along each side of the body is a row of 10—16 rather
obscure, more or less confluent, dark blotches. There

This paper is published by authority of the State of Illinois, IRS
Ch. 127, Par. 58.12, and is a contribution from the Section of Faunistic
Surveys and Insect Identification of the Illinois Natural History Survey.
Mr. Page is a research assistant at the Natural History Survey; Dr.
Smith is Head of the Section of Faunistic Surveys and Insect Identi-
Fan at the Survey and Professor of Zoology at the University of

inois.

COVER ILLUSTRATION:

Lawrence M. Page and Philip W. Smith

is a small, discrete, black caudal spot and a dark stripe
extending from the tip of the snout backward through
the eye. Usually there is no suborbital bar. The best
field character is the submarginal band of bright orange
in the spinous dorsal fin.

The male can be distinguished from the female at all
seasons and all sizes above 25 mm standard length by a
median row of enlarged specialized scales extending
from the midpelvic area to the anus. During late spring
and early summer the male has closely spaced melano-
phores over the breast and belly and on the ventral fins;
the female is white below and has only a few scattered
melanophores on the anal fin. The spinous dorsal fin
of the male is more heavily pigmented than is that of
the female, the basal portion being quite dark. For a
few weeks prior to spawning the female can be recognized
by its distinctly enlarged genital papilla; the genital pa-
pilla of the male is a small triangular flap.

The small young of the species can be readily dis-
tinguished from other young darters in the Mississippi
River valley by the combination of a slender habitus,
attenuate snout, and the characteristic dorsal spotting.

P. phoxocephala occurs from western Pennsylvania
to northeastern South Dakota—although it is for the
most part absent from the Great Lakes drainage—and
southward to northern Alabama and southern Oklahoma
(Fig. 1). The species is not found in the lower Mississip-
pi River valley and rarely occurs in low-gradient, low-
land streams anywhere within its range. In Illinois it
is widely distributed and generally common, except in
the northeastern and extreme southern parts of the state.

We are much indebted to Raymond T. Schaaf, Mrs.
Dorothy M. Smith, Norman D. Penny, Hartley F. Hutch-
ins, Robert O. Watson, Miss C. Catherine Huheey, and
the late Robert L. Hass for aid in collecting specimens; to
our entomologist colleagues Donald W. Webb and Drs.
John D. Unzicker and Milton W. Sanderson for their
help in identifying arthropod remains in darter stomachs;
to Dr. Marvin C. Meyer of the University of Maine for
identifying the leech parasite found on our P. phoxo-
cephala specimens; to Harman F. Smith, Illinois State
Water Survey, for providing data on the water chemistry
of the Embarras River; and to our associate Dr. R.
Weldon Larimore for counsel on various matters. We
also thank Chief Fishery Biologist A. C. Lopinot of the
Illinois Department of Conservation and his staff of

Adult female Percina phovxoccphala collected in May in the Embarras River,

Cumberland County, Illinois. From a drawing by Mrs. Alice Ann Prickett.

+

biologists for a considerable number of Illinois collections
of darters.

The drawings of P. phoxocephala and genital papillae
were done by Mrs. Alice Ann Prickett, University of
Illinois School of Life Sciences Artist. Assistance in pre-
paring the illustrations was provided by Illinois Natural
History Survey Technical Illustrator Richard M. Sheets
and Survey Photographer Wilmer D. Zehr. The manu-
script was edited by Robert M. Zewadski, Associate
Technical Editor of the Survey. Dr. David A. Etnier,
University of Tennessee, served as special guest reviewer.

THE STUDY AREA

The area selected for study (the shaded oval in the
lower-right quarter of Illinois in Fig. 1) extends from a
eravel bar in the middle Embarras River 2 mile north
of Greenup, Cumberland County, south to a site 3 miles
west of Rose Hill, Jasper County, IIl., although most
of the collections were made over gravel bars at Greenup.

The Embarras River, a tributary of the Wabash
River, flows through the Wisconsinan end moraines in

the vicinity of Charleston and has deposited large quanti-
ties of glacial gravel and sand for the entire length of
the study area. The water is well oxygenated by flowing
over the many fast riffles bordering sand and gravel bars
that alternate with deep, relatively quiet pools. Chemical
measurements taken in the Embarras River at Camargo
in Douglas County from October 1966 to April 1968 by
the Illinois State Water Survey and made available
through the courtesy of Mr. Harman F. Smith, indicated
that water quality was unusually high and that pollution
was minimal (Page & Smith 1970:5).

In the vicinity of the study area the stream could be
classed as a small to medium-sized river. During low
water stages the channel was only 15—30 feet wide and
in rifle areas barely a foot in depth, although there
were some deep pools at bridge sites and at abrupt bends
in the river. During flood stages the inundated flood-
plain was almost 1 mile wide.

One of the principal study sites, 1 mile west of
Greenup, had a variety of habitats, consisting of gravel
bars and gravelly raceways, sandbars and sandy race-
ways, a rubble riffle, and several silt-bottomed pools.

Fig. 2—Study area on the Embarras River 2 mile north of Greenup, III.

Another site, % mile north of Greenup, was similar
but had more extensive stretches of gravel (Fig. 2).

METHODS

Minnow-seine collections were made at 2-week in-
tervals from August to November 1967 and at irregular
intervals throughout 1968, 1969, and 1970 as material
was needed to obtain information for all seasons. A
total of 45 collecting and observation trips was made
to the study area between August 4, 1967 and September
AO L970!

In the field notes were made on the river and weather
conditions, pigmentation of the darters, and the habitats
in which specimens were captured. During the spring
and early summer months, water and air temperatures
were routinely recorded.

Occasionally various habitats were sampled to deter-
mine habitat preferences, but most efforts were concen-
trated in the channels, where the species was most easily
obtained. During the winter months numerous habitats
were sampled in an effort to find the overwintering habi-
tat of the species. Obtaining specimens during the win-
ter and during periods of high water proved difficult,
and no specimens were secured during January or De-
cember. Specimens collected during the 3-year study
period were distributed as follows: February, 1; March,
1; April, 1; May, 35; June, 50; July, 19; August, 16;
September, 75; October, 25; November, 15.

Supplemental specimens in the Illinois Natural His-
tory Survey ichthyological collection provided informa-
tion to help fill the gaps resulting from the difficulty of
collecting specimens during the cold months. A total
of 440 preserved specimens was examined in the study.
Only the 238 specimens collected and examined from
the study area were used for the growth measurements,
and only collections from the study area made during the
study period were used in discussions of population char-
acteristics,

Specimens were dropped into 10-percent formalin as
soon as they were captured. Later they were measured,
their age and sex were determined, and details of color
pattern and the presence of external parasites were noted.
Unless stated otherwise, all measurements given in the
text are standard lengths. Age determinations were
made by counting annuli on scales removed from just
above the lateral line below the junction of the spinous
and soft dorsal fins.

Some specimens from each collection were dissected
and examined for stomach contents, the presence of
macroscopic parasites in the alimentary canal, and gonad
condition. Gonads were measured, and a few were
blotted dry and weighed on a chain balance. Ovaries
showed significant increases in weight as the spawning
season approached, but testes were too small to be
weighed accurately. Ova were counted in several fe-
males. The stomachs of some potential predators of
P. phoxocephala were examined for darter remains.

5

Living P. phoxocephala specimens were brought to
the laboratory several times during the study to observe
their behavior in aquaria. When it became evident that
aquarium-held captives were not going to spawn, eggs
and sperm were stripped from ripe adults in several
unsuccessful attempts to obtain embryos.

On October 17, 1967 a quantitative sample was tak-
en ¥Y mile north of Greenup with an electric seine
(Page & Smith 1970:5) to estimate the composition
of the fish fauna at the site and the number of individuals
per areal unit of habitat.

HABITAT AND ASSOCIATED SPECIES

In the Kaskaskia River of Illinois, Thomas (1970:7)
found P. phoxocephala to be most abundant in the
middle river, rare in the headwaters, and occasional in
the lower river. The moderate-to-fast current over grav-
el and the high riffle-to-pool ratio in the middle river
were considered responsible for the increased abundance
in the middle river (ibid.:7, 16).

In Ohio, Trautman (1957:545) found P. phoxoce-
phala to be most common over “extensive bars and
riffes which contained clean sand and small gravel that
was almost free of silt.’ In Kansas, the species occurs
“in swiftly-flowing, shallow water, over a bottom of loose
gravel or of bedrock littered by stones” (Cross 1967:
292). In the portion of the Embarras River used for
both the P. sciera and the P. phoxocephala life-history
studies, the two species were generally found occupying
the same habitat, the relatively shallow, gravel-bottomed
portion of the river channel. P. phoxocephala was
somewhat less restricted to gravel than was P. sciera and
occasionally was taken in the channel over sand.

Collections from elsewhere in Illinois have revealed
more plasticity by P. phoxocephala in habitat choice
than was exhibited by the population in the Embarras
River. Specimens have been taken from small-stream
riffles, large rocky riffles, and even sandy pools of large
rivers. However, the abundance of P. phoxocephala in
the middle Embarras River indicates the optimal habitat
for the species to be the gravel-bottomed raceways of
medium-sized rivers with moderate current.

Juvenile P. phoxocephala remained in the spawning
habitat (shallow riffles along gravel bars) several weeks
after hatching. At approximately 1 month of age the
young darters moved out into the deeper water of the
channel.

Page & Smith (1970:6) summarized the species di-
versity in a section of the Embarras River blocked off
with minnow seines and sampled with an electroseine.
They found P. phoxocephala to be the second most com-
mon darter and the 13th most common species of fish;
it constituted 0.5 percent of the total fish population.
Collections taken in the other study areas over a 3-year
period tend to substantiate this numerical relationship
between P. phoxocephala and associated species.

The species most commonly associated with P. phoxo-

6

cephala were Notropis whipplei, N. spilopterus, N. stra-
mineus, Pimephales vigilax, Ericymba buccata, Percina
sciera, Hypentelium nigricans, Micropterus punctulatus,
and Phenacobius mirabilis.

REPRODUCTION
The Reproductive Cycle of the Male

Males were sexually mature and ready to spawn
during the first spring following their hatching. The
smallest male captured in spring was a 40-mm specimen
collected on May 27, 1969; although breeding pigmenta-
tion was absent in this fish, its testes were large (6 x
1.5 mm) and it apparently was capable of spawning,
as were all of the larger males collected in the spring and
examined for sexual maturity.

The larger the male, the earlier the breeding pigmen-
tation began to develop and the more intense it became
by spawning time. Males 2 years old collected on May
27, 1969 were considerably darker than females and
somewhat darker than 1-year-old males collected at the
same time. The brown vermiculations on the dorsum
were darkened in males, and in contrast to females,
the breast; belly; underside of the head; and membranes
of the anal, soft dorsal, and pelvic fins of the males were
covered with many expanded melanophores, giving them
an over-all dusky appearance (Fig. 3).

Besides the duskiness of the males, there was a pro-
nounced color difference between the sexes in the pig-
mentation of the soft dorsal fin. In addition to increased
melanization, the dorsal rays of males were boldly out-
lined with yellow; the soft dorsal fins of the females had
no visible yellow pigment.

Although the width and color intensity of the yellow-
orange submarginal band in the spinous dorsal fin were
usually greatest in males, pronounced variations occurred
in both sexes. The color varied from pale yellow to
bright orange.

Pigmentation changes began in April and peaked at
spawning time. The darker color of freshly captured,
large males taken in the spring made them easily sepa-
rable from females. Large size and more intense color-
ation undoubtedly enhanced sex recognition and provid-
ed older males an advantage over younger males in at-
tracting females.

Breeding P. phoxocephala males did not develop
tubercles. Collette (1965:577) found breeding tubercles
on none of the species of Swainia. The genital papillae
of males were small, triangular flaps which enlarged
slightly as spawning neared (Fig. 4).

The testes began enlarging in late summer, and con-
tinued to enlarge until spawning time. In specimens
collected on September 21, the length of the testes aver-
aged 10 percent of the standard length; in a specimen

Fig. 3
phala, both captured on May 26, 1970.

-Pigmentation patterns of a 63-mm breeding male

(top) and a 56-mm breeding female
} ‘

(bottom) Percina phoxoce-

collected on October 14,
percent; on May 27,
percent.

11 percent; on April 28, 19
15 percent; and on June 8, 21

The Reproductive Cycle of the Female

No difference between the pigmentation of breeding
females (Fig. 3) and that of non-breeding females was

D

Fig. 4.— Urogenital papillae of: A, male in the fall; B,
male in the spring; C, female in the fall; and D, female in the
spring.

discernible. Sexual dimorphism in P. phoxocephala
seems to be limited to the contrast between the “normal”
pigmentation of P. phoxocephala and the pigmentation
of breeding males, the difference in breast squamation,
and the presence of the specialized scales on the mid-
belly of males versus their absence on females.

In the spring the genital papillae of females were
enlarged, striated, conical structures (Fig. 4). In the
fall the papillae of females were morphologjcally similar
but proportionally much smaller than those of specimens
taken in the spring.

Females having attained a standard length of at least
42 mm were sexually mature at 1 year of age. All
spring-captured females examined that were 42 mm or
larger contained ova at least 1 mm in diameter and
were ready to spawn. ‘The only sexually immature
spring-collected female was a 38-mm specimen collected
on May 27, 1969.

The prespawning period was characterized by the
differentiation and maturation of ova; the spawning act
by the release of mature eggs; and the postspawning pe-
riod by the absorption of the remaining ova and recovery
of the ovaries. In P. phoxocephala, the recovery time
for females was very short, and enlargement of the ova-
ries began soon after spawning (Table 1).

Early stages of ova maturation proceeded slowly, but
aS spawning time approached, development was rapid.
The growth of ova was reflected in an increase in the
weight of the ovaries, which, in relation to body weight,
showed an exponential increase between July and the
following June (Fig. 5).

As with other fishes, developing ova were easily cate-
gorized into three groups based on size and color: the
smallest ova were white and less than 0.5 mm in diam-
eter; the intermediate were between 0.6 and 1.0 mm and
yellow; and the largest were 1.1—1.3 mm and yellow
to orange in color.

Ova categorized as intermediate were present in a
February-collected female (Table 2); large ova first
appeared in April. The proportion of small ova de-
creased as spring approached, and the proportion of
large ova increased. ‘The number of intermediate ova

Taste 1.—Lengths and weights of ovaries of Percina phoxocephala collected in different months of the year.

Length in mm

Weight in Grams

Standard Length Ovary Length Adjusted Weight Ovary Weight

Length of as Percent of Weight* of Both as Percent of

Collection Date of Female Ovary Standard Length of Female Ovaries Adjusted Weight
July 21, 1959 67 13 19.4 3.66 0.02 0.5
August 23, 1967 55 9 16.4 2.08 0.02 1.0
September 1, 1967 54 8 14.8 1.82 0.02 ait
October 22, 1967 57 11 19°53 2.39 0.06 D5
November 8, 1963 66 14 Pil? 3.02 0.09 S20
February 23, 1969 58 13 22.4 2.40 0.12 5.0
April 28, 1968 44 12 97.3 1.00 0.12 12.0
May 27, 1969 56 14 25.0 2.30 0.35 Waa
June 8, 1969 60 18 30.0 2.59 0.52 20.1

a Adjusted weight is the weight of the female minus the ovaries, stomach, and intestines.

OVARIAN WEIGHT AS PERCENT OF ADJUSTED BODY WEIGHT

ie}
JULY AUG. SEPT. OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUNF

Fig. 5—Increase in weight of ovaries in relation to body
weight from the end of one spawning season to the beginning
of the next.

remained between 9 and 24 percent in specimens col-
lected after late February.

Between 500 and 2,000 ova were produced by each
female in one season, but only about 10—50 percent
reached mature size. If we assume that darters lay all
the mature eggs, as suggested by Fahy (1954:166) and
Winn (1958b:181), each female P. phoxocephala lays
from 50 to 1,000 eggs in one season. The largest number
of mature ova actually counted was 720 in a 60-mm
female; the smallest number was 50 in a 45-mm female.
Karr (1963:235) counted the eggs in six P. phoxoce pha-
la from Iowa and found a range of 186—365. Large
females produced more eggs than did small females. The
mean number of mature eggs in three spring-collected
l-year-old females examined during this study was 83;
the mean number in six spring-collected 2-year-olds was
270.

Mature eggs stripped from ripe females were trans-
parent and adhesive, averaged 1.3 mm in diameter, and
contained one large oil droplet.

Spawning

The peak spawning period in 1969 was June 7—14,
and in 1970, June 5—12. In 1968 high water prevented
spring collections and presumably delayed spawning,

TasLe 2.—Differentiation and growth of ova in Percina
phoxocephala collected in the study area.

Percent of
Differentiated Ova

Estimated by Size Group

Percent of as SS eee
Differentiated 0.1-0.5 0.6-1.0 1.1-1.3

Collection Date Ova mm mm mm
October 3, 1967 30 100 (0) 0
November 17, 1963 40 100 0 0
February 23, 1969 80 81 19 0
April 28, 1968 over 90 75 7) 8
April 28, 1968 over 90 80 9 11
May 4, 1968 over 90 69 16 15
May 27, 1969 over 90 59 24 17
June 8, 1969 over 90 56 23 21
July 18, 1967 over 90 42 17 41

inasmuch as the spawning habitat (shallow gravel riffles)
was not available until sometime in July.

The spawning period for P. phoxocephala in central
Illinois varies with climatic conditions and presumably
may peak anytime after late May. Females heavy with
mature eggs were captured at Greenup in late May in
both 1969 and 1970, indicating that spawning could
occur that early in the year under ideal conditions.
Thomas (1970:8) collected ripe females in early August
in the Kaskaskia River at about the same latitude as
that of the Embarras River study area. He noted, how-
ever, that no ripe males were collected that late in the
year, and it is highly improbable that spawning would
occur later than early July in central Illinois.

The spawning habitat of P. phoxocephala is swift-
flowing water 15—60 cm (%—2 feet) deep over gravel.
Males move in mass into the spawning habitat well be-
fore the females do and presumably establish territories
although no actual observations of territoriality were
made. In 1970 males were common in the shallow water
along gravel bars as early as May 29. The ratio of males
to females captured in the shallow water on this date
was 15:1; on June 5 it was 11:2. The fish spawned
during the following week and by June 13 all adult
P. phoxocephala had left the spawning grounds.

Spawning could neither be observed in the field nor
induced in aquaria. The morphology and spawning
habitat of P. phoxocephala suggest, however, that mat-
ing and deposition of the eggs occur in a manner similar
to that described for other Percina species (New 1966;
Loos & Woolcott 1969; Reighard 1913; Winn 1953,
1958a, and 1958)).

Juveniles remain in the spawning habitat 2—4 weeks
after hatching. Several young were collected in the
shallow water (15—30 cm deep) along a gravel bar in
the study area where spawning was known to have oc-
curred 2 weeks before. With the young P. phoxocephala
(ranging from 19 to 27 mm) in the rifles were two
young P. sciera (19 and 21 mm) and one young P,
caprodes (33mm). Collecting in the shallow riffle areas
2 weeks later produced no young P. phoxocephala.

DEVELOPMENT AND GROWTH

Development

The smallest specimen available (18.7 mm standard
length, 22.4 mm total length) was collected in the study
area on June 23, 1970. Presumably a product of the
peak spawning period of June 5—12, the fish was esti-
mated to be 2 weeks old. Its body proportions (Fig. 6)
were essentially those of the adult, except that the head
and eyes were large in relation to the size of the body. The
head length was 32 percent of the standard length versus
an average of 27 percent of the standard length for 10
adults. Squamation was nearly complete; the only areas
lacking scales were the cheeks, opercles, nape, and the
anterior two-thirds of the belly.

SS} AMS>
Fig. 6.—Two-week-old Percina phoxocephala 19 mm in
standard length.

The pigmentation of this small specimen was weak
but showed the pattern characteristic of adults. The
dorsal spots, lateral blotches, band around the snout,
and spots in the fins of adults were represented by con-
centrations of melanophores. Yellow pigment in the
spinous dorsal fin indicated the beginning of the orange-
yellow band characteristic of the adult P. phoxocephala.
The lateral line was complete and fully pored. The head
canals were nearly complete except for a wide medial
interruption in the supratemporal canal.

Slightly larger specimens (21—23 mm) were almost
identical in morphology to the smallest specimen al-
though some had incomplete lateral lines. The special-
ized midyenter scales were discernible on males at about
23 mm, and the orange band was present in the spinous
dorsal fins of 25-mm specimens. At 27 and 28 mm,
scales were lacking only on the nape, and most individ-
uals had completed supratemporal canals. Scales were
not present on the nape until specimens reached a stan-
dard length of 33 mm.

The pigmentation of P. phoxocephala continued to
darken throughout life. Older individuals in any partic-
ular collection always were slightly darker than the
younger ones.

Growth

Standard length frequencies of specimens of P. phoxo-
cephala taken from the study area indicated that rapid
growth occurred during the first few months of life and
the growth rate diminished with age. The growth curve
for samples taken from the study area (Fig. 7) showed
a continuous average increase in size except during
October and November, when the mean standard lengths
of two samples averaged less than those of the Septem-

9
ber sample. This autumn reversal, which also occurred
in the study of P. sciera, is assumed to be the result
of an emigration of the larger fishes from the compara-
tively shallow raceways (most efficiently sampled) to
the deeper channel as winter approached.

Inasmuch as the average size of 12-month-old P.
phoxocephala specimens was 46 mm, the young fish at-
tained half of their Ist year’s growth in about 2 weeks.
Etheostoma gracile “attained almost half of their 1st
year’s growth in about | week” (Braasch & Smith 1967:
9). The growth rate of the Embarras River P. phoxo-
céphala population was faster than that found for the
Kaskaskia River population (Thomas 1970:14) and
much more rapid than that of the population in Boone
County, Iowa (Karr 1963:232). At the end of 1 year’s
growth, the Embarras River population averaged 45.7
mm in standard length; the Kaskaskia River population
averaged 45.3 mm in total length; and the Iowa popu-
lation averaged 34.1 mm in total length.

There is little indication of sex influence on size.

”
Ci) 2+ (28)
—C__ |+(57)
—tmin_ 12 mos. (22)
tin. 5 mos. (10)
in 4 mos. (18)
=
E —Cm _ 3 mos. (18)
= mm. 2 mos. (9)
in_ | mo. (18)
Oin_ 2 wks. (11)

70 680

Oo 10 20 30 40 50 60
STANDARD LENGTH, mm

Fig. 7—Growth of Percina phoxocephala in millimeters of
standard length. For each sample the horizontal line represents
range; the vertical line, mean; the hollow rectangle, one stan-
dard deviation to either side of the mean; and the black rec-
tangle, two standard errors to either side of the mean. Numbers
in parentheses are specimens measured. Samples of 1- and 2-
year-old fish included Embarras River specimens from outside
the study area.

10

Although the largest specimens collected in the study
area were males, the differences between male and fe-
male mean standard lengths at various ages were not
statistically significant. Thomas (1970:13) also found
no influence of sex on growth rate.

DEMOGRAPHY
Density

Four specimens of P. ploxocephala were taken in the
507 square yards of river quantitatively sampled by an
electric seine as described earlier. ‘The sample contained
750 fishes, an average of 1.48 fish per square yard (aver-
age depth 30 cm) and one P. phoxocephala per 169
square yards. Assuming that, rather than being uni-
formly distributed in the area sampled, P. phoxocephala
mainly occupied the gravelly raceway that constituted
about one-fourth (127 square yards) of the area, a more
realistic figure of one darter per 42.3 square yards of
gravel habitat results. Because of the inefficiency of
sampling by the electric seine and previous collecting in
the area, the figure of one darter per 42.3 square yards
may be rather low.

At two sites in the Kaskaskia River, Thomas (1970:
6) found more than 200 P. phoxocephala individuals
per acre of water, which is one darter for approximately
24 square yards of water, almost twice the density of
P. phoxocephala in the Embarras River. However, at
many other sites in the Kaskaskia River, the number
of P. phoxocephala individuals per acre was smaller than
that in the Embarras River study area.

Composition

Of the 238 P. phoxocephala collected in the study
area, 176 (74 percent) were young-of-the-year, 59 (25
percent) were l-year-old fish, and 3 (1 percent) were
2-year-old fish (Table 3). No specimens 3 years old or
older were examined, and in view of the sharp decrease
in numbers in each successive age class, it is doubtful
that in the Embarras River many individuals live to 3
or more years of age. Of 25 specimens from Boone
County, Iowa, examined by Karr (1963:232), five were
3 years and two were 4 years old.

Fig. 8—The habitats in the Embarras River
occupied by P. phoxocephala throughout the
year. The principal habitat, the gravel raceway,
is abandoned during the spawning period and
during the colder months of the year.

JAN. FEB.

MAR.

Tasie 3.—Distribution of sexes and year classes in Percina
phoxocephala taken from the study area between August 4,
1967 and September 20, 1970.

Number by Year Class

Sex —1 isp 2+ Total

Males 98 38 3 139
Females 72 21 0 93
Too small to sex 6 AS = 6
Total 176 59 3 238

Considerably more males than females were collected,
giving a sex ratio of 1.5 males to 1 female. The sex
ratio of the 170 young large enough to be sexed was
also skewed in favor of the males, although less than
that of the total sample (1.4:1). In the small sample
from the Kaskaskia River that Thomas (1970:14) used
to illustrate growth rate, there were 23 males and 18
females (1.3:1). However, much larger samples are
needed to determine the true sex ratio of these popula-
tions.

Although the data in Table 3 suggest that P. phoxo-
cephala males live somewhat longer than females, 12
of the 28 two-year-old fish examined for the data shown
in Fig. 7 were females. If there actually is a skewed
sex ratio in the population, more males than females
would be expected in any age class, and this factor
would obscure any sex influence on longevity.

The largest specimen examined by us was a 78-mm,
2-year-old male collected in the Kaskaskia River on
September 6, 1968. Trautman (1957:543) listed the
largest Ohio specimen as 4 inches long (approximately
100 mm total length).

Migration

P. phoxocephala exhibited the same annual migra-
tory pattern as that shown by P. scicra, 1.e., a late fall
emigration from and an early spring return to the gravel-
ly raceways (Fig. 8). Unfortunately, the habitat to
which the darters emigrated in winter could not be de-
termined. Quiet regions of the river, such as sluggish
backwater areas and pools and the deeper portions of

HIEMAL HABITAT

GRAVEL RACEWAYS
SPAWNING (RIFFLES)

APR. MAY JUNE JULY AUG. SEPT. OCT.

the channel, were seined, but no darters were found.
In February a specimen was collected in the relatively
shallow portion of the channel, but its occurrence there
was exceptional, and other attempts to collect specimens
in the winter months were unsuccessful. P. phoxocepha-
la left the raceway areas in November and returned in
March or April.

Besides the hiemal migration, the spring movements
into and out of the spawning area involved a large pro-
portion of the population and should be recognized as
a breeding migration characteristic of the species. Wheth-
er P. phoxocephala migrated in and out of tributaries
with the change in seasons as P. sciera was thought to
do is unknown.

Territoriality

Mass movements of the males into the spawning
habitat well before the females suggested that the species
was territorial during the spawning season. Aquaria
used to observe P. phoxocephala were probably too
small to allow the establishment of territories although
males were rather consistently belligerent toward other
males.

PHYLOGENETIC RELATIONSHIPS

In his description of Hadropterus nasutus, Bailey
(1941:1-2) suggested a close relationship with P. phoxo-
cephala and P. oxyrhyncha. Percina squamata, the
fourth species in the subgenus Swainia, is more general-
ized and less closely related, but it strongly resembles
P. phoxocephala in some characteristics, most notably
the pigmentation pattern.

Swainia is one of the most primitive subgenera of
Percina. Generalized characteristics of the subgenus
include the modest specialization of the midventral row
of scales in the male, lack of pronounced sexual dimor-
phism, highly pelagic habits, and high meristic counts.
Comparisons of data collected during this study and

Taste 4.—Stomach contents of Percina phoxocephala of all sizes collected in the Embarras River.

are numbers of stomachs examined.

11

during the life-history study of P. sciera indicate Swainia
to be somewhat less evolutionarily advanced than the
subgenus Hadropterus.

Winn (1958b:188) suggested the degree of abate-
ment of the gas bladder to be an indicator of phyloge-
netic advancement of darters. Page & Smith (1970:11)
found P. sciera to have a large bladder, averaging ap-
proximately 16 percent of the standard length of the
fish examined. In eight P. phoxocephala specimens
the bladder was also large, ranging from 11 to 18 per-
cent and averaging 15 percent of the standard length.

DIET AND FEEDING HABITS

Thomas (1970:8-12) examined the stomach con-
tents of 103 P. phoxocephala from the Kaskaskia River,
Illinois. He found the predominant food items to be
“baetid nymphs, chironomid larvae, and hydropsychid
larvae,’ and noted that certain organisms (e.g., stonefly
naiads and elmid beetle adults), although abundant in
the darter habitat, were avoided as food items by all
four darters he studied. The young fed mainly on
midge larvae.

In 45 specimens of P. phoxocephala from the Embar-
ras River study area examined for stomach contents
(Table 4), midge larvae and pupae, black fly larvae,
caddisfly larvae, and mayfly naiads formed over 99 per-
cent of the food items encountered. Less frequent items
were amphipods, fish eggs, and terrestrial insects.

The small variety of food items found in P. phoxo-
cephala was also found in P. sciera studied in the same
area. In addition to a similarity in over-all diet, the
seasonal variations in the diets of the two species were
approximately concurrent; dipterans and mayflies pre-
dominated during all seasons, and caddisflies formed a
large portion of the diet during the summer (Fig. 9).
The correlation between the two fish species in seasonal
variations in diet strongly suggests that both fed on
whatever insect immatures were available and palatable,

Figures in parentheses

Percent of Stomachs Examined in Which Each Food Organism Occurred

Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov.
Food Organism (1) (2) (4) (4) (9) (9) (4) (4) (4) (4)
Midge larvae, pupae 100 100 25 50 44.4 55.6 50 100 75 50
Black fly larvae 100 Bes 100 25 Weis ee BG 25 ae
Caddisfly larvae 100 says 25 25 Die: 44.4 25 50 50 fe
Mayfly naiads say shi 75 100 66.7 66.7 oF 50 25 50
Miscellaneous sai ace ae 25 cao Seiets 25 An a0 25
Mean Number of Food Organisms Per Stomach

Feb. Mar. Apr. May June July Aug. Sept Oct. Nov
Midge larvae, pupae 5.00 3.00 0.25 Pdf) 1.89 3.33 1.00 157.79 Seo 0.75
Black fly larvae 1.00 Bess 15.50 15.50 6.00 0.44 ar 0.50
Caddisfly larvae 1.00 w20 0,25 0.44 aha) 0.25 1.50 75 RES
Mayfly naiads weles 125 Pathe) 4.33 1.00 ere 0.50 2.50 (O) 743)
Miscellaneous 0.25 0.25 0.25

12

and that the variation was mainly an expression of cycles activity were in the months following spawning (July and
in insect populations. August) and in the colder months (November, Febru-
The heaviest feeding occurred in May as the spawn- ary, and March).
ing season approached. ‘The periods of least feeding As the darters increased in size, the over-all diet
100
30
80
2)
z 70
Fig. 9—Seasonal variation in EF
the diet of Percina phoxocephala a 60
specimens of all sizes. The per- Ss
centage of each food item repre- As 50
sents its contribution to the total °
: . E 40 a
number of items found in all fish > IDGE & BLACKFLY
examined each month. uw
a 30
WW
a
20
10
10)

FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV.

MIDGE

NW &

MAYFLY [ _] CADDISFLY
BLACKFLY

PERCENTAGES

Fig. 10—Composition of the diets of five
size-classes of Percina phoxocephala. Numbers
in parentheses are specimens examined.

composition progressed from one dominated by dipteran
larvae to include substantially greater portions of the
larger mayfly and caddisfly immatures (Fig. 10). The
smallest specimen (19 mm) available for dissection con-
tained one mayfly naiad. Aquarium-held darters fed
readily on a variety of foods, including fish and shrimp
flesh, earthworms, snails, isopods, and tadpoles of Pseud-
acris triseriata.

Some geographic variation in diet is to be expected,
although other reports on the food of P. phoxocephala
have indicated basically the same composition. In a
study conducted in Iowa, Karr (1963:234) found may-
flies to be the most common food organisms, with dipter-
an and caddisfly larvae constituting the remainder of
the diet. Additional items encountered include dragon-
fly naiads and water boatmen (Forbes 1880: 23; Forbes
& Richardson 1920:286; Cross 1967:293).

INTERACTIONS WITH OTHER ORGANISMS
Competition

Observations of P. phoxocephala and P. sciera for 3
years revealed no overt competition between them or
with any other coinhabitants. However, covert compe-
tition among species is more difficult to discern, and in
field studies can only be suggested in terms of similarities
in life histories and niche requirements. P. sciera and
P. phoxocephala share certain ecological characteristics
(e.g., similar diets, habitats, breeding habitats) in the
Embarras River, and competition between them (and
perhaps with other species) may intensify to the point
of population limitation in certain seasons of the year.
For example, food may become limiting in winter.

Predation

No evidence of predation on P. phoxocephala was
found in the study area. Concurrent with the life-history
studies of the darters, an investigation was conducted
on the feeding habits of the most abundant large predator

13

in the river, Micropterus punctulatus (Smith & Page
1969). ‘The only darter remains encountered as food
items were those of Etheostoma nigrum. Thomas (1970:
16) also found no evidence of predation on P. phoxo-
cephala.

Parasitism

During the summer and fall, adult and young darters
were often parasitized by a small leech, identified by
Dr. Marvin C. Meyer as Piscicolaria reducta Meyer
(Piscicolidae). Darters with leeches attached were col-
lected from late June into November; more than half
of those collected in October and November were para-
sitized by one to eight leeches of various sizes. Attach-
ment was usually to the caudal fin, sometimes to the
caudal peduncle or a pectoral fin. In some cases fin
rays showed slight damage.

Of 45 P. phoxocephala individuals dissected for food
analysis, one had one small nematode in its intestines,
and another had three nematodes. Another darter of
this species from Henry County, IIl., had two small acan-
thocephalans in its intestines.

Hybridization

The only literature report known to us of natural
hybridization involving P. phoxocephala is that by
Thomas (1970:16) on two specimens of Percina macu-
lata x P. phoxocephala hybrids from the Kaskaskia River
at Sullivan, Ill.

SUMMARY OF LIFE-HISTORY DATA ON
P. PHOXOCEPHALA AND P. SCIERA

A comparison of the life histories of P. phoxocephala
and P. sciera reveals a few ecological and demographic
differences and many similarities (Table 5). The differ-
ences reflect divergent specialization. The similarities are
due, in part, to the relatively close relationship between
the two darters and to the fact that both species were
investigated in the same study area.

TasLe 5.—Summary of life-history information on Embarras River populations of Percina phoxocephala and P. sciera."

Characteristic

P. phoxocephala

P. sciera

Principal habitat

Spawning habitat

Habitat of juveniles

Age at reaching sexual maturity
Size at reaching sexual maturity
Sexual dimorphism in spring
Breeding tubercles

Number of mature ova counted
Description of egg

Usual peak spawning period
Territoriality

Adult morphology nearly complete
Influence of sex on growth rate
Longevity suggested by study
Influence of sex on longevity
Maximum size suggested by study
Sex ratio among young
Migrations

Principal diet

Gravel raceways of moderate-sized rivers
Gravel rifles 15-60 cm deep

Gravel riffles

1 year

Males about 40 mm; females about 40 mm
Slight in pigmentation

Absent

50-720

1.3 mm in diameter, transparent, adhesive
Early June

Probable during spawning season

At 3 weeks

None

2+ years

Males 2+ years; females 2+ years

78 mm

1.4 males: 1 female

Breeding; hiemal

Aquatic insect immatures

Gravel raceways of moderate-sized rivers
Gravel riffles 30-90 cm deep

Gravel riffles

1 year

Males about 50 mm; females about 40 mm
Pronounced in both pigmentation and size
Absent

80-196

1.5 mm in diameter, transparent, adhesive
Early June

Probable during spawning season

At 3 weeks

Males grow faster than females

4+ years

Males 4+ years; females 3+ years

108 mm

1.1 males: 1 female

Breeding; hiemal; tributarial

Aquatic insect immatures

4“ Supportive data in Page & Smith (1970).

14

LITERATURE CITED

Bartey, Reeve M. 1941. Hadropterus nasutus, a new darter
from Arkansas. University of Michigan Museum of Zool-
ogy Occasional Papers 440. 8 p.

Braascu, Marvin E., and Pump W. SmitH. 1967. The
life history of the slough darter, Etheostoma gracile (Pisces,
Percidae). Illinois Natural History Survey Biological
Notes 58. 12 p.

Co.tette, Bruce B. 1965.
ing tubercles in fishes of the family Percidae.
tional Museum Proceedings 117 (3518) :567-614.

Cross, Frank B. 1967. Handbook of fishes of Kansas.
University of Kansas Museum of Natural History Miscel-
laneous Publication 45. 357 p.

Fany, Wituiam E. 1954. The life history of the northern
greenside darter, Etheostoma blennioides blennioides Rafin-

Systematic significance of breed-
U.S. Na-

esque. Elisha Mitchell Scientific Society Journal 70(2):
139-205.
Forses, S. A. 1880. The food of fishes. Illinois State Lab-

oratory of Natural History Bulletin 1 (3): 18-65.

, and Ropert Ear Ricwarpson. 1920. The fishes
of Illinois. 2nd ed. Illinois Natural History Survey.
exxxvi -|. 357 p.

Karr, James R. 1963. Age, growth, and food habits of
johnny, slenderhead, and blacksided darters of Boone Coun-
ty, Iowa. Towa Academy of Science Proceedings 70:
228-236.

Loos, Jutes J., and Witiiam S. Wootcort. 1969. Hybrid-
ization and behavior in two species of Percina (Percidae).
Copeia 1969 (2): 374-385.

Netson, E. W. 1876. A partial catalogue of the fishes of

Illinois. Illinois State Laboratory of Natural History
Bulletin 1(1) :33-52.

New, Joun G. 1966. Reproductive behavior of the shield
darter, Perctna peltata peltata, in New York. Copeia 1966
(1) : 20-28.

Pacer, LAwreNnceE M., and Puitie W. Smirn. 1970. The life
history of the dusky darter, Percina sciera, in the Embarras
River, Illinois. Illinois Natural History Survey Biological
Notes 69. 15 p.

ReicHarp, JAcos. 1913. The breeding habits of the log-
perch (Percina caprodes). Michigan Academy of Science
Report 15:104-105.

SmitH, Puiip W., and Lawrence M. Pace. 1969. The
food of spotted bass in streams of the Wabash River drain-
age. American Fisheries Society Transactions 98(4) :647—
651.

Tuomas, Davin L. 1970. An ecological study of four darters
of the genus Percina (Percidae) in the Kaskaskia River,
Illinois. Illinois Natural History Survey Biological Notes
7AO), als} yor

Trautman, Mitton B. 1957. The fishes of Ohio. The
Ohio State University Press, Columbus. 683 p.

Winn, Howarp Exuiotr. 1953. Breeding habits of the percid
fish Hadropterus copelandi in Michigan. Copeia 1953(1):
26-30.

—————. 1958a. Observations on the reproductive habits
of darters (Pisces-Percidae). American Midland Natural-
ist 59(1) :190-212.

——. 1958b. Comparative reproductive behavior and

ecology of fourteen species of darters (Pisces-Percidae) .
Ecological Monograph 28(2) :155-191.

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