Effects of High Chronic Temperatures and Diel Temperature Cycles on the Survival and Growth of Lahontan Cutthroat Trout

Tests of chronic temperature tolerance indicated that the upper limit for survival and growth of Lahontan cutthroat trout Oncorhynchus clarki henshawi was between 22°C and 24°C. Lahontan cutthroat trout experienced complete mortality within 2 d at 28°C and approximately 60% mortality over 7 d at 26°C. Fish suffered no significant mortality at temperatures of 24°C and below. No significant differences in growth of fish held at 22°C relative to fish held at cooler temperatures were found, but significant reductions in growth were observed at 24°C. When fish were subjected to fluctuating temperatures similar to field conditions, which cycle daily from 20°C to 26°C, they still grew, though not as much as fish maintained at constant 13°C or 20°C. Exposure to diel temperature fluctuations did not affect tolerance of subsequent chronic elevated temperatures.