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1 ,. <br />h d- (`mil 5?('1Q [E ® M! <br />5 arr a <br />INFLUENCE OF TEMPERATURE ON DEVELOPMENT AND HATCHING <br />SUCCESS OF NATIVE COLORADO RIVER FISHES <br />Paul C. Marsh and Mark S. Pisano <br />Assistant Professor (Research) and Student, respectively, <br />Center for Environmental Studies, <br />Arizona State University, Tempe, Arizona 85287 <br />Abstract <br /> Razorback sucker, (Xyrauchen texanus), bonytail chub (Gila elegans), humpback <br /> chub (G, cypha), and Colorado squawfish (Ptychocheilus lucius) eggs were <br /> spawned and fertilized at 17C, and ova then incubated at 5, 10, 15, 20, 25, <br /> and 30C. Total mortality of all ova occurred in 12-96 hours at 5, 10, and <br /> 30C; and in 48-60 hours at 15C for P. lucius only. Survival and percentage <br /> hatch was highest at 15-20C (G. elegans) or 20C (all others). Hatched <br /> prolarvae were 0.2-1.3 mm TL longer at 20C than at 15 or 25C. Spinal or <br /> other anomalies were more frequent at 15 and 25C than at 20C. Development <br /> rates were similar for all species, 4.4-6.1 (15C), 8.4-9.9 (20C), and 12.4- <br /> 18.8 (25C). Development rate (V): temperature (T) relationships, defined <br /> 2 <br />as V = mT + b, were similar for all species, all were highly significant (r <br /> 0.77-0.99), and indicated a "zero development" temperature range of 8.6C <br />j' (G, elegans) to 12.2C (P. lucius). Because of lower survival and significantly <br /> higher incidence of anomalies at 15 and 25C, the optimal temperature for <br /> development and hatching of these species is probably near 20C. This <br /> suggests that reproduction may be limited by low water temperatures throughout <br /> much of the Colorado River, although successful hatching is certainly not <br /> precluded. Other hypotheses to explain the real or apparent demise of these <br /> fishes in the River, such as predation upon young, should be examined. <br /> <br />434