7785

• UCREFRP Catalog Number: 7785
• Author: Thompson, J. M.
• Title: The Role of Size, Condition, and Lipid Content in the Overwinter Survival of Age-0 Colorado Squawfish.
• USFW Year: 1989.
• USFW - Doc Type: Colorado State University,
• Copyright Material: NO

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higher than in wild fish. If wild age-O Colorado squawfish
depleted their lipid reserves at the same rate as my starved
hatchery-reared fish, the majority of the wild fish would
exhaust their energy stores and perish overwinter. However,
unlike my laboratory fish, the lipid content of wild age-O
Colorado squawfish did not decline significantly overwinter.
The failure to detect any significant difference between
fall and spring lipid levels among wild fish may be due to
three factors. First, if overwinter mortality occurred in
the Colorado River in the stretch we sampled, my spring
lipid values would be biased high since only surviving fish
(which would have had higher lipid content than non-survivors)
were analyzed. Another possible explanation is that my fall
sample was collected before water temperatures had fallen
below the 130 C growth threshold. Fish may have been able
to accumulate additional lipid reserves between the time of
my collection on 1 October 1988, when backwater temperatures
ranged from 12.2 to 25.00 C (mean = 16.90 C), and the
beginning of winter (when water temperatures fell below 130
C in late october). Finally, age-O Colorado squawfish in
the lower Colorado River may maintain their lipid reserves
overwinter by feeding. My laboratory observations of active
swimming and feeding behavior exhibited by age-O Colorado
squawfish demonstrate that they will feed at winter
temperatures if food is available. Stomach analyses
conducted by the Larval Fish Laboratory at Colorado state