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March 1985 Marsh-Incubation Temperature and Fish Survival 133 ently linear over the range of temperatures at which hatching occurred, but is curvilinear over a broader range (Kinne and Kinzie, 1962; Blaxter, 1969; Lagler et al., 1977). Because hatching occurred at only three test temperatures, a curvilinear expression could not be derived. REsuLTS.-Temperature and Dissolved Oxygen.-Actual test temperatures (Table 3) were near the desired means for all experiments except "5°C nom- inal", which were 7.3, 7.3, and 6.8°C for bonytail chub, humpback chub, and Colorado squawfish, respectively. Dissolved oxygen remained within 3% of saturation at each temperature during all trials (Table 3). Temperature Effects on Survival and Hatch.-Razorback sucker.- Percentage hatch of razorback sucker was highly dependent on incubation temperature (Table 4), with greatest success at 20°C (35%) and 25°C (29%), and significantly lower success at 15°C (19%). All eggs died at 5, 10, and 30°C. Greatest mortality at all temperatures occurred before embryos attained motility within the chorion. Time to peak hatch decreased with increasing temperature from 216 h (15°C) to 84 h at 25°C. Newly-hatched normal pro- larvae were 6.5-8.6 mm TL and were active, wriggling and squirming on the bottom. Once able to move vertically they swam upward for several cm, then ceased motion and sank slowly, tail first. This cycle was repeated 2 to 3 times/min. Swimup (neutral buoyancy) was attained at 103-312 h, depend- ing upon temperature (Table 4). Normal fry were 8,4-8.6 mm at swimup. Incidence of stunted and deformed fry was significantly lower at 20°C (8.1% of total hatch) than at 15°C (14.5%) or 25°C (32.2%). Bonytail chub.-Percentage hatch of bonytail chub was highly dependent upon incubation temperature (Table 4), with statistically equivalent success (35 and 32%) at 15 and 20°C, respectively. Hatch at 25°C was 0.5% and no hatch occrred at 5, 10, or 30°C. Mortality again was greatest before embryos attained motility within the chorion. Time of peak hatch decreased with increasing temperature from 204 It at 15°C to 103 h at 20°C. Newly-hatched prolarvae averaged 6.0-6.3 mm, with no significant differences among temperatures. Prolarvae were weakly motile after hatching, remaining quies- cent unless disturbed. As larvae began actively swimming they moved upward in the water column then ceased motion and sank slowly, head first. Many larvae apparently adhered to sides of incubation chambers with the anteroventral portion of the head contacting the solid surface and the body extending perpendicularly. When such larvae were displaced they performed a directed swimming motion back toward an attachment surface, butting several times until regaining contact. The mechanism of adhesion is as yet unknown. Swimup was attained at 148-396 h and increased with decreasing temperature (Table 4). TL of normal fry at swimup was greatest at 20°C (8.6 mm) compared with 15 and 25°C (8.1 mm). Incidence of abnormal fry ranged from 0-4% of total hatch and was unrelated to temperature, although the largest percentage occurred at 15°. Humpback chub.-Results for humpback chub were similar to those for bonytail. Percentage hatch was dependent upon temperature (Table 4), with greatest success at 200C (60%). Hatch was significantly lower at 15°C (0.8%) and 25°C (2%). All embryos died at incubation temperatures of 5, 10, and 30°C. All mortality occurred prior to attainment of embryonic motility