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136 The Southwestern Naturalist vol. 30, no. I within the chorion. Time to peak hatch decreased with increased tempera- ture from 156 It (15°C) to 72 hrs (25°C). Newly hatched normal prolarvae were longest at 15°C (63 mm) compared with 5.5 and 5.7 mm at 20 and 25°C respectively. Behavior of hatched prolarvae was the same as for bony- tail. Swimup occurred at 372 h at 151C to 166 h at 25°C, depending on temperature (Table 4). Swimup fry were 8.2-8.5 mm at 20 and 25°C; no lengths were obtained for swimup fry at 151C. Incidence of abnormal fry was significantly greater at 15°C (33%) than at 20 or 25°C (13% and 17%, respectively). Colorado squawfish.-Percentage hatch of squawfish was 27% at 20°C in trial I, and 2% (20°C) and 9% (251C) in trial II (Table 4). All ova died at 5-15, 25, and 30°C (trial 1) or 5-15, and 30°C (trial II). As with other species, most mortality occurred before embryo motility was attained. Peak hatch was at 78-108 h at 20°C (both trials) compared with 63 h at 25'C. Hatched normal prolarvae averaged 5.5 mm at 20°C and 5.6 mm at 25°C. Prolarvae were seemingly helpless at hatching, moving feebly on the bot- tom. However, larvae reacted to bright light by frantic, apparently undi- rected swimming activity, which ceased within 15-30 s after removal of the light source. This increased activity also was observed in prehatch embryos, which vibrated within the chorion when exposed to bright light under a microscope. Abnormal fry accounted for 26% of total hatch at 25°C more than twice the 11% incidence at 20°C (Table 4). Development Rates.-Development rate (V, Table 4) at each temperature was similar for all species, 4.4-6.1 (15°C), 8.4-9.9 (20°C), and 12.4-18.8 (25°C). Yet, linear development rate versus temperature function slopes for pairwise species comparisons were significantly different (F-test for equality of slope, p < 0.05) between Colorado squawfish and razorback sucker, humpback chub and razorback sucker, and between Colorado squawfish and bonytail chub. These comparisons likely reflect basic differences in developmental physiology among species. DISCUSSION.-Results herein are generally consistent with earlier work (Toney, 1974; Inslee, 1982; Harriman, 1981a-b, 1982a-b; Bulkley et al., 1981), clearly demonstrate that survival and hatch are maximum near 20°C and show that mortality increases dramatically with < 10°C change from that temperature. Potential effects of adult acclimation temperature upon embryo survival and hatch at various incubation temperatures cannot be assessed, although effects have been noted with some species (e.g., Koenst and Smith, 1976) and might reasonably be expected (Brett, 1956). Although every attempt was made to standardize variables other than temperature, factors remain which may have influenced results: fungus on devloping egges, health and condition of broodfish, differences between wild-caught and hatchery-reared or maintained individuals, manipulation and handling, induced spawning as compared with "natural ripening" of broodfish, and unknown differences between the experimental system and natural incubation conditions. These could influence absolute values of sur- vival or percentage hatch at a given temperature, but should have influenced relative relationships (differences in percentage hatch among temperatures)