Thermal Performance of Three Rainbow Trout Strains at Above-Optimal Temperatures

Studies have predicted declines in trout habitat of over 50% given projected climate warming scenarios. Therefore, knowledge of the performance of trout strains at elevated temperature is critical for management of trout fisheries and trout strains under climate change. Our objectives were to compare the performance of three strains of Rainbow Trout Onchorynchus mykiss at elevated temperatures. We compared growth, consumption, and feed efficiency at 20 degrees C and 22 degrees C, and critical thermal maxima (CTM) among the strains. The Case Western strain is registered as a warm-tolerant strain with the National Fish Strain Registry, and it did achieve a significantly higher CTM (31.29 degrees C) than the Kamloops (31.14 degrees C) but not the Wytheville (31.20 degrees C) strain. Such small differences are likely not biologically significant. While the CTM of the Case Western strain was higher than that of the Kamloops, the Case Western strain consistently performed poorer than the other strains in feeding and growth experiments at 20 degrees C and 22 degrees C. Our results add to the growing body of literature suggesting that differences in thermal performance do exist between strains of trout. While there is debate about whether these differences are due to evolutionary adaptation to local environmental conditions or phenotypic plasticity, the differences being found in thermal performance of trout suggests future research aimed at improving thermal performance via thermal testing and selective breeding may yield stock with improved tolerance and growth at warmer temperatures.