LAUSR

Cold-water dependent rainbow trout (Oncorhynchus mykiss) inhabit a considerably diverse geographic range extending from Alaska to southern California, where adjustments in growth and swim performance in response to temperature may be present. Here we measured four clonal lines of rainbow trout for growth and sprint speed, at two different constant temperatures (10 or 18 °C), across 12 weeks. The objective was to characterize temperature responses among different genotypes originating from Alaska, Oregon, and two hatchery populations; we expected that the lines would respond in a way that implicated their diversity in geographic origin and domestication history. We observed all fish achieve the greatest growth and body size and fastest sprint speed at 18 °C, regardless of origin; substantial variation in growth and swim performance among and within line and temperature was also observed. Surprisingly, the Swanson line from Alaska exhibited very rapid growth at the warmer temperature, which may support the countergradient variation in growth hypothesis. The diversity of responses reported here illustrates the complex nature of the relationship among temperature, growth, and performance and provide groundwork for future genetic analyses utilizing clonal lines of rainbow trout.