9572

• UCREFRP Catalog Number: 9572
• Author: Bestgen, K. R.
• Title: Interacting Effects of Physical and Biological Factors on Recruitment of Age-0 Colorado Squawfish.
• USFW Year: 1997.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

42.5 h), suggesting that once hatching began at any temperature, times to midpoint and
end of hatching were about equal across all temperatures. In general, swim bladder
inflation and first feeding occurred sooner at higher temperatures and also at fluctuating
temperatures.
Lengths oflarvae.--Length at hatch (Table 1) differed significantly for
temperature level but not for regime, or interaction (Table 2). Lengths were significantly
different in 18 and 26°C treatments, but not in the 22 and 26°C or 18 and 22°C treatments.
Lengths at d 7 differed significantly for regime and interaction but not for temperature
level. Most interaction significance was due to faster growth in the fluctuating regime at
22°C.
Discussion
Hatch and survival.--Results presented here generally corroborate those of
previous laboratory studies. I also found hatch and larval survival were generally higher
over a wider range of temperature conditions than previously reported. This may reflect
the low density of embryos and the rapid exchange of water in our incubation chambers
which minimized fungal infection and oxygen deprivation. Differences in hatch and
survival at 18-26°C and 30°C may partly reflect the fact that these treatments were done
in different years with embryos from different broodfish.
High hatch and survival of larvae were observed in all treatments except 30°C, a
temperature rarely recorded in river channels in the upper Colorado River basin. Summer
water temperatures of 30°C were found in the former range of Colorado squawfish in the
lower Colorado River (Dill 1944). However, it is likely that Colorado squawfish there
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