Abstract
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.