UiNlVLRSiTY OF
ILLINOIS LIBRARY

URBANA-CHAMPAIGN
BIOLOGY

FIELDIANA
Zoology

Published by Field Museum of Natural History

Volume 72, No. 3 December 19, 1977

Trachelyichthys exilis,

A New Species of Catfish

(Pisces: Auchenipteridae) from Peru

DAVID W. GREENFIELD

DEPARTMENT OF BIOLOGICAL SCIENCES
NORTHERN ILLINOIS UNIVERSITY

and

DIVISION OF FISHES
FIELD MUSEUM OF NATURAL HISTORY

and

GARRETT S. GLODEK

DIVISION OF FISHES
FIELD MUSEUM OF NATURAL HISTORY

ABSTRACT

Trachelyichthys exilis n. sp. is described from the Rio Mambn, Peru, on the basis
of three specimens. The new species is the second known member of the genus
Trachelyichthys previously known only from a single individual of T. decaradiatus
from Surinam. T. exilis is compared with T. decaradiatus and a redescription of the
latter is presented.

RESUMEN

So describe una nueva especie de la familia Auchenipteridae, Trachelyichthys
exilis, basada en tres ejemplos desde el Rio Mam6n, Peru. Antes del descubrimiento
de estos ejemplos, el genero Trachelyichthys se habia conocido por un solo ejemplo
de su especie tipo, T. decaradiatus, describida por Mees (1974) desde Surinam. T.
exilis se distingue de T. decaradiatus por tener la cabeza mas ancha y altas, la dis-
tancia predorsal mas larga, la espina pectoral mas alargada, la placa dorsal mas
ancha, el hocico mas corto, las bases de las aletas dorsal y anal mas largas, las bar-
bas mandibulares exteriores y maxilares mas largas, y el proceso posterior del la
elavicula de poca altura.

Mees (1974) described the monotypic genus Trachelyichthys and
its species T. decaradiatus on the basis of a single individual (56.5
mm. SL) taken in the Karanambo area, Rupununi, Surinam. On
July 24, 1975 we collected three additional specimens of this genus

US ISSN 0015-0754

Publication 1272 vw" 47 vJMIV 6(

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University of Illinois

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48

FIELDIANA: ZOOLOGY, VOLUME 72

in Peru, in the Rio Mamon, a tributary of the Rio Nanay, approxi-
mately 25 km. west of Iquitos (03°42'S, 73°16'W). The three speci-
mens (FMNH 80476, FMNH 80477, CAS 39168) were taken in a
shallow (approximately 1 m.) backwater area over a mud and sand
bottom. The Rio Mamon is a blackwater river and the surface water
temperature was 28°C at the time of capture.

The three specimens represent the second known species of Trach-
elyichthys. The new species is compared with T. decaradiatus and a
redescription of the latter is presented.

METHODS

Counts were made with the aid of radiographs; measurements
were made to nearest 0.1 mm. using dial calipers and are presented
as percent of standard length. All fin-ray elements were counted
individually rather than tallying the last two as a single ray. Verte-
bral counts are post-Weberian complex vertebrae and include the

cl

cw

FIG. 1. Method of measuring coracoid width (cw) and length (cl) on ventral body
surface, coracoid process (cp), mental barbels (mb), pectoral fin spine (ps).

GREENFIELD & GLODEK: NEW CATFISH 49

terminal half-centrum and urostyle as one element. The following
measurements were made by placing one point of the calipers and
the tip of the snout (both squared at a 90° angle) lightly against the
edge of a vertical surface; predorsal-fin length; snout length; snout-
pectoral fin distance; snout-pelvic fin distance; snout-anal fin dis-
tance. All measurements from the snout to a fin are to the origin of
that fin. Head width and depth are measured at the widest portion
of the cleithrum. Body depth and width are measured at the origin
of the pelvic-fin bases. Predorsal-fin length is measured from the
snout to the posterior edge of the dorsal plate just anterior to the
dorsal-fin spine. Cleithrum length is measured by placing one point
of the calipers in the notch in the cleithrum just anterior to the
pectoral-fin spine and the other point on the end of the posterior
cleithral process. Pectoral-fin spine length is measured by placing
one point of the calipers in the notch in the cleithrum just anterior
to the pectoral-fin spine and the other on the tip of the spine. Dorsal-
fin spine length is measured by placing one point of the calipers in
the notch at the posterior edge of the dorsal plate and the other
point on the end of the spine. Coracoid width is measured by placing
the points of the calipers on the posterior-most ends of the coracoid
( fig. 1 ). Coracoid length is measured by placing one edge of the cali-
pers on the posterior-most end of the coracoid and the other on the
posterior-most edge of the coracoid at the midline of the body,
which can be located by running a fingernail over the central portion
of the U formed by the coracoid. Dorsal plate width is measured by
placing the points of the calipers against the bony edges of the
narrowest portion of the dorsal plate anterior to the dorsal-fin spine.
Interorbital width is the least bony interorbital width. Diameter
of the eye is the greatest horizontal dimension of the eyeball. Other
counts and measurements follow Hubbs and Lagler ( 1964).

MATERIAL EXAMINED

Trachelyichthys decaradiatus — BMNH 1971.7.29.30 - Holotype.
Trachelyichthys exilis n. sp. — See type material.
Trachelyichthys exilis n. sp. Figures 2-5.

Holotype. - FMNH 80476, 68.8 mm. SL.

Paratypes. - FMNH 80477, 42.3; CAS 39168, 42.4 mm. SL.

Diagnosis. — May be distinguished from T. decaradiatus by
possessing a wider head (29.5-30.8, mean 30.2 vs. 26.5), a deeper

oq
06

C

50

GREENFIELD & GLODEK: NEW CATFISH

51

1 cm

FIG. 3. Lateral view of head of holotype of Trachelyichthys exilis. A, posterior
cleithral process, B, opercle, C, dorsal plate, D, pectoral fin.

head (22.6-24.3, mean 23.7 vs. 19.6), a longer predorsal distance
(29.5-31.5, mean 30.3 vs. 28.3), a longer pectoral-fin spine (26.2-27.4,
mean 26.7 vs. 20.2), a wider dorsal plate (8.2-8.5, mean 8.4 vs. 6.7),
a shorter snout (2.6-4.0, mean 3.2 vs. 4.2), a longer dorsal-fin base
(9.0-10.3, mean 9.6 vs. 8.0), a longer anal-fin base (39.9-45.2, mean
41.7 vs. 37.9), a longer maxillary barbel (36.6-38.7, mean 37.9 vs.
27.8) reaching to rear of dorsal fin in T. exilis and to front of dorsal-
fin spine in T. decaradiatus, a longer outer mandibular barbel (28.4-
34.3, mean 31.4 vs. 26.0) reaching to past base of dorsal-fin spine in
T. exilis and to front edge of dorsal-fin spine in T. decaradiatus,
and a shallower posterior cleithral process (3.3-3.5, mean 3.4 vs. 4.2)
(fig. 3).

52

FIELDIANA: ZOOLOGY, VOLUME 72

FIG . 4. Pectoral-fin-spine of holotype of Trachelyichthys exilis.

Description. — Data for holotype presented first, followed in
brackets by values for para types, plus means for morphometric
data in parentheses. Dorsal-fin elements 1,4 (1,4 & 1,5); anal-fin
elements 36 (36 & 37); pelvic-fin elements 10 (10); pectoral-fin
elements 1,6 (1,6); vertebrae 31 (31).

Length of head 24.4 [27.3 & 28.6] (26.8); width of head 29.5 [30.3
& 30.8] (30.2); depth of head 24.3 [22.6 & 24.3] (23.7); depth of
body 33.0 [25.5 & 29.1] (29.2); width of body 17.4 [12.9 & 13.0]
( 14.4); predorsal length 31.5 [29.5 & 30.0] (30.3); length of cleithrum
22.7 [21.2 & 21.5] (21.8); greatest depth of posterior cleithral process
3.5 [3.3 & 3.3] (3.4); length of pectoral-fin spine 26.6 [26.2 & 27.4]
(26.7); length of dorsal-fin spine 25.7 [18.9 & 19.6] (21.4); length of
coracoid 10.3 [7.1 & 7.6] (8.3); greatest width of coracoid 20.9 [19.1 &
20.0] (20.0); dorsal plate width 8.4 [8.2 & 8.5] (8.4); bony interorbital

p -

= J3

0 .3

~ s

OC

1

-

o

I

1

3

53

54 FIELDIANA: ZOOLOGY, VOLUME 72

width 12.5 [12.0 & 12.8] (12.4); diameter of eye 8.7 [8.5 & 8.7] (8.6);
length of snout 2.6 [3.1 & 4.0] (3.2); width of gape 14.5 [12.3 & 13.7]
(13.5); length of dorsal-fin base 9.0 [9.7 & 10.1] (9.6); length of
anal-fin base 45.2 [39.9 & 40.1] (41.7); length of upper caudal-fin
lobe 29.1 [25.9 & 30.3] (28.4); length of lower caudal-fin lobe 25.1
[23.1 & 25.3] (24.5); length of caudal peduncle 10.6 [10.2 & 11.1]
(10.6); depth of caudal peduncle 15.1 [14.2 & 14.4] (14.6); distance
from snout to pectoral-fin origin 17.6 [20.0 & 20.3] (19.3); distance
from snout to pelvic-fin origin 45.6 [42.4 & 45.6] (44.5); distance
from snout to anal-fin origin 57.4 [51.4 & 54.4] (54.4); length of
maxillary barbel 38.5 [36.6 & 38.7] (37.9); length of outer mandi-
bular barbel 31.5 [28.4 & 34.3] (31.4); length of inner mandibular
barbel 7.6 [6.6 & 7.1] (7.1).

Dorsal-fin spine smooth on anterior surface, posterior surface
with 44 (holotype) small barbs. Pectoral-fin spine with barbs on
both anterior (23 in holotype) and posterior (20 in holotype) sur-
faces, those on anterior surface slightly larger (fig. 4). Lateral line
developed over its entire body length, but only conspicuous from tip
of posterior cleithral process posteriorly to caudal-fin origin.

Color in alcohol. — (of holotype) Head and body cream with dark
brown to black markings; top of head mostly black, sides of head
mottled with black; opercular membrane cream with scattered
brown pigment; ventral surface cream from anus forward to an-
terior edge of coracoid where there is a heavy concentration of
brown pigment following contour of coracoid bone, forward to tip
of lower jaw; inner and outer mental barbels cream, contrasting
with brown chin; maxillary barbels black dorsally and cream ven-
trally; sides of body with a black, blotchy stripe running from
supraclavicle posteriorly along lateral line to caudal-fin base, an-
terior portion of stripe forming a large blotch which almost fills
tympanum over air bladder, an area surrounded dorsally by dorsal
plate, anteriorly by supraclavicle and ventrally by posterior clei-
thral process; posterior cleithral process surrounded by black,
forming a short black stripe which extends from tip of posterior
cleithral process towards anal-fin origin; dorsal midline cream
(viewed from top) with a black stripe below on either side, beginning
about one eye-diameter behind dorsal-fin base and running pos-
teriorly to caudal-fin base; areas between black stripes cream, over-
laid by a heavy peppering of brown pigment ; caudal fin cream with
brown spots tending to form vertical bars; basal portion of anal
fin with a peppering of brown pigment as on body, center portion of

GREENFIELD & GLODEK: NEW CATFISH 55

fin cream (forming a longitudinal light band), distal portion heavily
pigmented with black; pelvic fins cream with a black band on distal
margin and another about one- third distance from base of fin;
pectoral fins with black pigment covering most of first three rays
and distal portion of fourth, last two rays cream, dorsal fin with
black on membranes of anterior portion, last two rays cream.

Color of the young- (para types) General coloration of body and
head paler than adult; head with a large black blotch on top, pos-
terior to eyes, two small blotches posterior to large blotch and in
advance of dorsal-fin origin; black stripes on body of adult broken
up into a series of blotches in young; several brown blotches present
between midline of body and anal-fin base.

Color in life, (taken from a 35 mm. Kodachrome of holotype).
Color pattern as described above for holotype with following ex-
ceptions: ventral surface white instead of cream; cream color re-
corded for rest of body with a pinkish tinge; mandibular barbels
yellowish; cream color of caudal fin with a yellowish tinge.

Name. — exilis, slim or slender, referring to the slender posterior
cleithral process..

Trachelyichthys decaradiatus Mees. Figures 6 and 7.

Additional information on the holotype of T. decaradiatus is
presented for comparison with T. exilis. Standard length 56.5 mm.

Dorsal-fin elements 1,4; anal-fin elements 36, pelvic-fin elements
10; pectoral-fin elements 1,6; vertebrae 31.

Length of head 24.9; width of head 26.5; depth of head 19.6;
depth of body 28.1; width of body 11.7; predorsal-fin length 28.3;
length of cleithrum 19.8; greatest depth of posterior cleithral pro-
cess 4.2; length of pectoral-fin spine 20.2; dorsal-fin spine broken;
length of coracoid 7.8; greatest width of coracoid 19.5; dorsal plate
width 6.7; bony interorbital width 11.8; diameter of eye 8.5; length
of snout 4.2 ; width of gape 12.9 ; length of dorsal-fin base 8.0 ; length
of anal-fin base 37.9; length of upper caudal-fin lobe 25.8; length of
lower caudal-fin lobe 22.6; length of caudal peduncle 10.3; depth of
caudal peduncle 14.5; distance from snout to pectoral-fin origin
18.2; distance from snout to pelvic fin origin 43.0; distance from
snout to anal-fin origin 53.8; length of maxillary barbel 27.8; length
of outer mandibular barbel 26.0; length of inner mandibular barbel
7.8.

56

FIELDIANA: ZOOLOGY, VOLUME 72

0 1cm

FIG. 6. Lateral view of head of holotype of Trachelyichthys decaradiatus , BMNH
1971.7.29.30, A, posterior cleithral process, B, opercle, C, dorsal plate, D, pectoral
fin.

DISCUSSION

Trachelyichthys exilis is clearly a member of the genus Trachely-
ichthys, described by Mees in 1974. Trachelyichthys is the only
auchenipterid genus having the combination of 10 pelvic-fin ele-
ments, a truncate caudal fin and lacking an adipose fin. Trachely-
ichthys exilis is easily distinguishable from the only other member
of the genus, T. decaradiatus, by its much shallower posterior
cleithral process (fig. 3) in addition to differing in a number of body
proportions, the most important being a wider and deeper head,
a wider dorsal plate, and a longer pectoral-fin spine.

GREENFIELD & GLODEK: NEW CATFISH

57

FIG . 7. Pectoral-fin spine of holotype of Trachelyichthys decaradiatus.

The discovery of T. exilis in Peru illustrates the general pattern
of faunal similarities between the Peruvian Amazon and the distant
drainages of the Guianas, where T. decaradiatus occurs. Lowe-
McConnell (1975) points out that the areas peripheral to the central
Amazon basin exhibit greater similarities among themselves than
they do with the fauna of the central basin, the Peruvian Amazon
having more than 100 species in common with the Guianas. Lowe-
McConnell interprets this pattern as the remnants of a primitive
fauna that had spread around the Amazon basin when it was pos-
sibly a marine gulf, which later was replaced by large lakes. Mees
(1974) suggested that Trachelyichthys is most closely related to
Trachelyopterus, a genus which occurs in the central Amazon basin.
If indeed Trachelyichthys is a member of a primitive fauna then
Trachelyopterus might have been derived from this genus.

58 FIELDIANA: ZOOLOGY, VOLUME 72

ACKNOWLEDGEMENTS

We are grateful to Teresa Greenfield and George Gutierrez for
assistance in field work and to Hernan Gutierrez for providing
transportation in his boat from Iquitos. Alwyne C. Wheeler, British
Museum (Natural History), kindly loaned the holotype of T. decara-
diatus. Teresa Greenfield reviewed the manuscript and prepared
the Spanish abstract. Zbigniew T. Jastrzebski, Field Museum,
drew Figures 2 to 7 . This research was supported by Department of
Interior Contract No. 14-16-0008-786 to Southern Illinois University
at Edwardsville.

REFERENCES

HUBBS, C.L. and K.F. LAGLER
1964. Fishes of the Great Lakes region. Univ. Mich. Press, Ann Arbor. 213 pp.

LOWE-MCCONNELL, R.H.

1975. Fish communities in tropical freshwaters, their distribution, ecology and
evolution. Longman, London, 337 pp.

MEES, G.F.

1964. The Auchenipteridae and Pimelodidae of Surinam (Pisces, Nematognathi).
Zool. Verh. Rijksmus. Nat. Hist. Leiden ( 132), 256 pp.

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