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<br />embryo incubation temperature for Colorado squawfish was determined to be 20-22°C <br />(Hamman 1981; Marsh 1985). <br />The narrow optimum temperature range for Colorado squawfish embryo <br />incubation suggested by laboratory studies was not expected given the highly variable <br />temperature regimes found during the spawning season of this species. Colorado <br />squawfish in the unregulated Yampa River, Colorado, may spawn when water <br />temperatures range from 16 to 26°C (Nesler et al. 1988, Tyus 1990). The relatively wide <br />temperature range during presumed reproduction by Colorado squawfish in the wild <br />suggests that the optimal temperature range for embryo incubation found in previous <br />laboratory studies may be too narrow. This study was conducted to determine effects of <br />water temperature and of constant and fluctuating temperatures on hatch of embryos, and <br />on survival and development of Colorado squawfish larvae. <br />Methods <br />Colorado squawfish embryos were obtained from the Dexter National Fish <br />Hatchery and Technology Center, Dexter, New Mexico. Embryos used in the 18-26°C <br />treatments in 1991 were from wild fish captured from the Colorado River,. near Grand <br />Junction, Colorado. The wild adults were held in ponds and allowed to ripen naturally <br />until 14 June, which is 0-4 weeks earlier than wild Colorado squawfish spawn in upper <br />Colorado River basin (Nesler et al. 1988; Tyus and Haines 1991). Embryos used in the <br />30°C treatment in 1992 were from a mixed, upper Colorado River broodstock held in the <br />Dexter hatchery; these fish were allowed to ripen naturally in ponds until 29 May. <br />Colorado squawfish were artificially spawned following injections with common carp <br />10 <br />