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The higher hatch at lower temperatures and higher post-hatch survival at higher <br />temperatures observed in this study may suggest that these are differences in physiological <br />tolerances of embryos and larvae and may represent adaptions to particulaz habitats. <br />Colorado squawfish may spawn in the 16-26°C main channel habitat (Kesler et al. 1988; <br />Tyus and Haines 1991). Lazvae emerge from the substrate after an undetermined period, <br />drift downstream, and occupy 25-28°C, low-velocity channel margin habitats. Field <br />evidence suggests that larger (older) Colorado squawfish larvae and juveniles pre~~•~ <br />backwater habitat (Tyus 1991 b; Tyus and Haines 1991, Haines and Tyus 1991), where <br />warmer water promotes faster growth and better survival. Furthermore, movements of <br />marked age-0 Colorado squawfish suggest they seek warmer water (Tyus 1991 b). <br />If optimal embryo hatch and larval survival temperatures aze indeed different, then hatch <br />and larval survival may not be independent at some temperatures due to the experimental <br />design used in this study. In the 30°C treatment, which is marginal for hatch, survival of <br />larvae may be confounded by the low number and poor condition of embryos that hatched. <br />Survival of larvae hatched in cooler temperatures and then acclimated and reared at 30°C <br />might have been higher than that of larvae hatched and reared at 30°C. <br />Hatch was not significantly different in fluctuating and constant regimes. Survival of <br />larvae to d 7 was higher in fluctuating temperatures (11-31 %), due largely to high survival <br />in the fluctuating regime and low survival in the constant regime in the 18°C treatment. <br />Abnormalities <br />Abnormalities were apparent in all fish from the 30°C treatment, but incidence was lower <br />at 18-26°C and similar to that observed by Mazsh (1985) at 20 (11%) and 25°C (26 %). <br />11 <br />