Behavioral thermoregulation of largemouth bass,Micropterus salmoides,and bluegill,Lepomis macrochirus,in a nuclear reactor cooling reservoir

Synopsis Behavioral responses which allow largemouth bass, Micropterus salmoides, and bluegill, Lepomis macrochirus, to survive under unusually high temperature conditions were examined. Distribution of fish was ascertained by angling. Body temperatures of 4 fish were obtained using radio transmitters. Temperatures of other fish were measured after fish were captured by angling. Both species were restricted in range by lethal water temperatures and therefore inhabited a greater portion of a thermally altered reservoir in winter than in summer. Under unheated conditions (during reactor shutdown), bass occupied shallow areas with an abundance of submerged logs and stumps, a deep area with springs, and a cove where the effluent canal entered the reservoir. Commencement of reactor operation resulted in an increase in water temperature to more than 50°C in summer. Bass and bluegill retreated to three refuges and remained there until the reactor shut down and the reservoir cooled. In the refuges, bass experienced a wide variety of temperatures, but adults generally avoided temperatures above 31°C. Large adult bass (>40 cm) occupied particular positions in a refuge cove, medium size bass (15–40 cm) swam in the open water, and small bass (