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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26

similarly found that mortality of age-O fish during wintE~r
results from exhaustion of stored energy reserves (Oliver et
ale 1979; Isely 1981; Henderson et ale 1988).
Whether an age-O Colorado squawfish survived overwinter
was a function of both size and feeding regime. Unlike the
fish in other studies (Oliver 1977; Toneys 1977), some of my
captive Colorado squawfish were offered food (either pellets
or brine shrimp) throughout the winter period. After an
initial phase of 2-3 weeks that followed acclimation to
winter temperatures, duting which feeding behavior was
minimal or absent, all size classes fed readily during their
twice-weekly (pellets) or daily (brine shrimp) feedings.
Feeding activity was inversely related to fish size, with
small fish exhibiting the most active.feeding behavior.
Cunjak (1988, p. 44~) found that "early winter is a
stressful period of acclimatization to rapidly changing
environmental conditions". Perhaps the initial 2-3 week
stage of non-feeding exhibited by Colorado squawfish
correlates to this stressful "early winter period". After
three weeks, the fish had acclimated sufficiently to winter
conditions to begin feeding.
The low percent survival exhibited by starved small and
medium fish (Figure 3) provides compelling evidence to
support the premise that to survive through their first
winter, age-O Colorado squawfish must either accumulate a
certain critical amount of lipid prior to winter or feed