6012

• UCREFRP Catalog Number: 6012
• Author: Miller, W. H., D. L. Archer, H. M. Tyus and K. C. Harper.
• Title: Colorado River Fishery Project
• USFW Year: 1982.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

Juvenile temperature preference tests showed preferred temperature
that ranged from 21.9°C to 27.6°C with an estimated final preferendum of
24.6°C, which was approximately the same as that for adults. In the
course of temperature studies, several fish were quickley disabled by
high temperatures of 30°C and 35°C when transfered from acclimation
temperatures of 14 and 20°C respectively. The swimming ability of
juveniles too was affected by temperature. For example, their swimming
performance (min. to fatigue) dropped from 120 min given a velocity of
0.43 m/s at both 20 and 26°C, to only a mean of 16.8 minutes at 14°C.
To complete its life cycle, the Colorado squawfish requires water
temperatures of 20 to 28°C from mid June to October. A temperature of
about 20°C is required for spawning while temperatures that are near
24°C, the preferred temperature, are needed for optimal development and
growth of young.
Total Dissolved Solids
Total dissolved solids (TDS) preference of juvenile Colorado squaw-
fish was determined in the laboratory (Appensix~. They preferred TDS
concentrations of 600 to 1100 mg/1, the lowest available and completely
avoided concentrations greater than 4,400 mg/1. TDS concentrations in
the Green and Colorado Rivers seldom exceed 2000 mg/1, therefore, TDS
levels are probably not affecting distribution of squawfish in the main
Green and Colorado Rivers. However, the Dolores River is far above
avoidance concentrations in September. High TDS levels in the Dolores
River ( 6000 mg/1) probably are one reason no squawfish were found there
during this study. Also, irrigation returns and ditches may reach TDS
levels that squawfish avoid and are one reason squawfish are not often
found in these areas.
Bioassays
Post larval and YOY squawfish were exposed to a variety o~•chem-
icals in bioassay studies at the University of Idaho (Appendi The `-
chemicals that were tested are known to occur in the Upper Colorado
River system and have the potential of afflicting the Colorado River
fishes. The results of 96 hour static toxicity tests show that the
Colorado squawfish is more resistant to heavy metals (Hg, Cd, Se, Zn)
than the northern squawfish and the humpback chub. Also, the Colorado
squawfish apparently is more resistant to pesticides (DDT, dieldrin,
endrin, parathion and methyl) than the rainbow trout, channel catfish
and bluegill, but slightly less resistant than the humpback chub (for
DDT and parathion). With DDT and endrin, the Colorado squawfish proved
to be more resistant than the northern squawfish. However, the northern
squawfish was more resistant to endrin than the Colorado squawfish.
L
Heavy metals were greatly affected by water quality. Mercury and
copper could not be tested adequately because they tended to precipitate
in hard simulated Colorado River water (~ 300 mgll CaCO ). In the `
Colorado River system where water hardness levels are quite Iow, such as