3017

• UCREFRP Catalog Number: 3017
• Author: Suttkus, R. D. and G. H. Clemmer.
• Title: The Humpback Chub,
• USFW Year: 1977.
• Copyright Material: NO

NUMBER 1, 1977

Figure 14 illustrates the deepest bodied juvenile (low-
er) that we have from the Grand Canyon area. The
upper specimen shows a blunt snout, short pectoral fins
and a moderately deep body. The middle specimen has
a sharp snout, moderate cephalic dip, long pectoral fins
and a moderately deep body. The lower specimen has a
blunt snout, slightly less than a moderate cephalic dip,
extremely short pectoral fins and an extremely deep body
as mentioned above.
Figure 15, upper and middle specimens have a mod-
erate body depth and a relatively sharp snout. However,
they differ to some degree in sharpness of snout, hooking
of snout, and depth of cephalic dip. The reader should
note that the upper and middle illustrations are of speci-
mens that differ approximately five centimeters in stan-
dard length. Too, the lower specimen illustrates a speci-
men approximately twelve centimeters larger than the
middle individual. All illustrations in figures 10 through
14 are enlargements of young or juvenile specimens. The
upper two illustrations in Figure 15 are also enlarge-
ments of juvenile specimens, but the lower illustration
in Figure 15 is a reduction of the actual size of an adult
female specimen. The three specimens illustrated in Fig-
ure 16 and the two specimens illustrated in Figure 17
are adults. The authors had no adult specimens from
the Grand Canyon area that exhibited the extreme snout
and hump development which was illustrated by Miller
(1946) and by Minckley (1973).
Figure 16 illustrates three of the four adults taken
from the mouth of the Little Colorado River. The lower
illustration of Figure 15 is that of the fourth specimen
from the Little Colorado River taken in June 1976. The
head profiles are similar for all four. The upper illustra-
tion of Figure 16 is that of the male and the middle and
lower specimens are females as well as the lower speci-
men of Figure 15. The male specimen was illustrated in
color by Williams and Finnley (1977). The pectoral
fins are proportionately shorter in the three females than
in the male. The male has small tubercles (pearl organs)
on the head, body and fins as described below.

Figure 17 illustrates the male and female salvaged
specimens from Powell Reservoir. Neither specimen
seems to be typical of Gila cYPha in all respects, but we
do not suggest they are hybrids. We interpret the differ-
ences as being within the variation of the species. The
ventrally arched body of the male tends to negate the
height of the nuchal hump. However, the mouth is ven-
tral and the eye small. Although the arching tends to
pull the pectoral fins forward, in its appressed position,
it nearly reaches the insertion of the pelvic fins whereas
the pectoral of the female (lower illustration of Figure
17) is not as long proportionately and extends somewhat
short of the insertion of pelvics. The tuberculation of
both specimens is described below.

Based on the consistency of data presented in the
scattergrams, and our extensive comparisons of various
specimens, we conclude that all our material from the
Grand Canyon is referable to Gila cYPha.

3

Growth and Developm.ent

The smallest specimen (24.6 mm SL) does not have
pectoral fin rays fully developed. Specimens up to 28
mm in standard length may not have a full compleme~t
of pectoral fin rays. Lateral line scale development. IS
the reverse of that in some fishes. Instead of a postenor
to anterior development the first lateral line scales de-
velop in the anterior region. Lateral line scales were not
sufficiently developed to make a count on 34 o~ the 74
young and juveniles. Specimens under 30 mm m stan-
dard length have fewer than ten lateral line tubes or
grooves and no scales. Specimens from 30 to 35 mm have
up to 35 scales partially or entirely dev~loped and ~p t.o
45 tubes developed. The full lateral hne scale senes IS
not developed until a standard length of around 50 mm
is attained. Scale development above and below the
lateral line is also progressive with age. Specimens from
50 to 100 mm in standard length vary in having a few
rows (four to six) below and (six to eight) above the
lateral line to seven to ten rows below and ten to twelve
rows above. The size and exposure of the scales decrease
dorsally and ventrally away from the lateral line. Thus
toward the back and belly in general the scales are
smaller and embedded. The largest specimens are com-
pletely scaled on the back, the breast and the belly.
Scales on the back are small, embedded and spaced to
some extent. The breast scales vary from small and em-
bedded to well developed; however, they are not as large
as lateral body scales. The belly scales are well developed.
The posterior scales in the lateral line at the, base of
the caudal are nearly typical in shape, but antenorly on
the narrow part of the peduncle, the lateral line scales
are very elongate. These elongate scales grade anteriorly
into scales of more typical shape which make up the an-
terior third to half of the lateral line row.

Meristic Characters and Measurements

Frequency distributions of fin rays, vertebrae and scale
counts are given in Table 1 and Table 2. Other authors
mentioned above have pointed out that fin-ray, scale and
vertebral counts are not diagnostic characters for the
humpback chub, Gila cypha. We present. the data par-
tially for the sake of completeness and partIally to enable
a comparison with additional samples from the same ~rea
and particularly with samples from other are~s. MIl!er
(1946) gave counts for two specimens. Gaufm, SmIth
and Dotson (1960) had 15 specimens available, but fre-
quency tabulations of fin-ray counts were not presented.
Holden and Stalnaker (1970) gave range and mean
values for dorsal and anal fin-ray counts, number of
vertebrae and number of gill rakers for 16 specimens,
but did not present frequency tabulations., Minckley
(1973) presented usual fin-ray counts, a~d m the key,
gave the figure of more than 81 lateral-h~e scales, .but
did not state number of specimens exammed. MIller
(1946) gave lateral-line scale count of 77-80 in Table 2,
and we presume the two numbers (77 and 80) a~e the
counts of the two specimens. The dorsal and anal fm-ray