7379

• UCREFRP Catalog Number: 7379
• Author: Tyus, H. M.
• Title: Potamodromy and Reproduction of Colorado Squawfish in the Green River Basin, Colorado and Utah
• USFW Year: 1990
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

MOVEMENTS OF COLORADO SQUA WFISH

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...

imprinting occurs, it must do so at an early stage
of development, because larval Colorado squaw-
fish pass out of the spawning areas within a few
days after hatching (Nesler et al. 1988).
Sexually mature Colorado squawfish spawned
in declining flows and increasing water tempera-
tures after spring runoff. The spawning period be-
gan about 38 d after highest spring flows. The
longer interval between peak flow and spawning
dates noted in most high-flow years was associated
with cooler river temperatures due to an extended
runoffperiod. Conversely, this response time was
shorter in lower-water years, presumably because
river temperatures were warmer. Although re-
gressions were not significant for temperature-
spawning response correlations, this was presum-
ably due to the difficulty in obtaining evidence of
a significant effect from one environmental factor
with only 5 years of data, especially when several
factors may be involved (Ricker 1975). However,
the timing of spawning that I report is further sup-
ported from collections of newly hatched larvae
by Haynes et al. (1984) and Nesler et al. (1988).
As noted for other cyprinids (Maksunov 1971),
adult Colorado squawfish used inundated shore-
line and lowlands during spring runoff, presum-
ably feeding or reducing their exposure to high-
velocity water flow, or both. This behavior may
help fish to prepare for the large energy expendi-
ture required during migration and spawning. Non-
annual spawning of some fish noted in my study
perhaps reflected an endogenous control influ-
enced by the high energetic cost of migration.
The annual cycle of gametogenesis in Colorado
squawfish is not well understood, but there is ev-
idence that the cycle is extended. R. L. Hamman
(USFWS, personal communication) observed egg
development in Colorado squawfish brood stock
soon after they spawned at Dexter (New Mexico)
National Fish Hatchery. Rapid ovarian develop-
ment soon after spawning has also been noted by
others for common carp Cyprinus carpio (re-
viewed by Bye 1984). Thus, gonadal development
in female Colorado squawfish may begin 8-9
months before spawning migrations occur. As in
other cyprinids, there may also be a long period
of gonadal dormancy in females during winter
when gonadotropic activity is low and egg devel-
opment is suspended (Billiard et al. 1978; Bye
1984). Low winter temperatures may be essential
for normal gonadal proliferation of males, as it is
in some other cyprinids (Ahsan 1966). Egg mat-
uration (vitellogenesis and final maturation) pre-
sumably resumes in spring with warming water

...

temperatures, increasing flows, water quality
changes, and perhaps other factors.
Colorado squawfish females with secondary sex
characters were seldom captured in my study. A
lack of secondary sex characteristics in suspected
females was also noted by Hamman (1981) in
hatchery-reared fish. He found that only a few ripe
female fish developed tubercles, and then only
slightly. Toney (1974) also noted heavy tubercu-
lation of males and apparent absences of tubercles
in hatchery-reared females. He also reported that
males in captivity produced sex products during
summer, but females required injections of cho-
rionic gonadotropin to facilitate ovulation. Four
wild females injected with carp pituitary spawned
within 24-48 h, and 10 hatchery-reared females
ovulated 24 h after injection (Hamman 1981).
I observed the development of sexual maturity
(Le., breeding coloration, tubercles, sex products
present) in 12 male Colorado squawfish held in
tanks of cold well water (about lOoC). The only
observable stimulus for this maturity was change
in photoperiod from sunlight filtering into the lab-
oratory from windows. However, four known and
two suspected females were not ripe, suggesting
that the presence of ripe males in the absence of
other environmental cues was not sufficient to
stimulate ovulation. Captive female common carp
have been observed to sustain huge increases in
gonadotropic hormones that, in the absence of a
suitable environment, did not result in ovulation
(Billiard et al. 1978; Stacey 1984).
When proper conditions exist, final maturation
of and gamete release by Colorado squawfish may
occur within a short time period. Suspected fe-
male Colorado squawfish captured early (before
other ripe fish were taken) on the spawning grounds
were apparently not in reproductive condition (no
sex products, no tubercles, little coloration). How-
ever, capture of spent and a very few ripe females
suggested that only a brief period was required for
final maturation and spawning. Nesler et al. (1988)
reported that spawning could occur in a very short
time after abrupt increases in river flow. If envi-
ronmental factors-substrate, lunar cycles, social
interactions, photoperiod, water velocity, and
temperature (Bye 1984; Stacey 1984)-influenced
final maturation and gametic release in this spe-
cies, these factors were present in both spawning
sites each year of this study. Other factors, such
as metabolite inhibition (Chen and Martinich
1975), were not evaluated.
Fidelity to spawning areas was demonstrated
here and by Wick et al. (1983), but it has yet to