7772

• UCREFRP Catalog Number: 7772
• Author: Bestgen, K. R. and M. A. Williams.
• Title: Effects of Fluctuating and Constant Temperatures on Early Development and Survival of Colorado Squawfish.
• USFW Year: 1994.
• USFW - Doc Type: Fort Collins, Colorado.
• Copyright Material: NO

and no hatch at the other temperatures. Optimum embryo incubation temperature for
Colorado squawfish was determined to be 20-22°C (Hamman 1981; Marsh 1985).
The narrow optimum temperature range for Colorado squawfish embryo incubation
suggested by laboratory studies was not expected given the highly variable temperature
regimes found during the spawning season of this species. Colorado squawfish in the
unregulated Yampa River, Colorado, may spawn when water temperatures range from 16 to
26°C (Nester et al. 1988, Tyus 1990). The relatively wide temperature range during
presumed reproduction by Colorado squawfish in the wild suggests that the optimal
temperature range for embryo incubation found in previous laboratory studies may be too
narrow.
This study was conducted to determine effects of water temperature and of constant and
fluctuating temperatures on hatch of embryos, and on survival and development of
Colorado squawfish larvae.
Methods
Colorado squawfish embryos were obtained from the Dexter National Fish Hatchery and
Technology Center, Dexter, New Mexico. Embryos used in the 18-26°C treatments in 1991
were from wild fish captured from the Colorado River, near Grand Junction, Colorado.
The wild adults were held in ponds and allowed to ripen naturally until 14 June, which is
0-4 weeks earlier than wild Colorado squawfish spawn in upper Colorado River basin
(Nester et al. 1988; Tyus and Haines 1991). Embryos used in the 30°C treatment in 1992
were from a mixed, upper Colorado River broodstock held in the Dexter hatchery; these
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