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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28

is critical to overwinter survival, field studies to ,;
determine if age-O Colorado squawfish feed during winter
(and the extent of available food) are essential. cunjak
and Power (1987) determined that wild brook and brown trout
feed continuously throughout the winter. Despite continued
feeding, they found that condition factor in both species
declined to the yearly low in winter. cunjak and Power
hypothesized that low winter condition was due to either the
inability of the trout to effectively assimilate ingested
food or to the fact that energy intake was insufficient to
balance metabolic costs. The metabolic costs of my captive
Colorado squawfish were undoubtedly lower than the metabolic
costs of wild fish. The aquarium-held fish lived in a
comparatively benign environment free. from currents,
temperature fluctuations, and other fish species that may be
predators or competitors; all of which would increase
metabolic demands on wild fish. In addition, minimum
temperatures achieved in my aquaria (2.5-3.00 C) were higher
than the near 00 C minimum temperatures to which wild age-O
Colorado squawfish are exposed. Shul'man (1974) noted that
the fat content of wintering fish drops more quickly at
progressively lower water temperatures.
Prior to the onset of winter, the mean lipid content of
my hatchery-reared fish was almost twice that of wild fish
of similar size (28.9% vs. 14.9%). Wood et ale (1957) also
found that lipid levels in hatchery-reared salmonids were