Some relationships of upper thermal tolerances to preference and avoidance responses of the bluegill

Temperature tolerance, preference, and avoidance studies were conducted on the bluegill (Lepomis macrochirus) in Conowingo Pond, lower Susquehanna River, Pa. Upper incipient lethal temperatures of 23.3, 29.3, and 35.80C were determined for bluegill (mean total length 90 mm) acclimated at 1, 13, and 270C, respectively. The results agree with published information on bluegill. Median resistance temperatures were plotted against linear regressions of preference and avoidance temperatures. Preferred temperatures were 4 to 50C less than median resistance temperatures. Bluegill acclimated at temperatures greater than or equal to 130C avoided short-term (96 hr) lethal temperatures. Median resistance time for bluegill acclimated at 13 and 270C leveled off and exceeded 96 hr near the avoidance temperature. Avoidance temperatures exceeded lethal temperatures at acclimation temperatures less than 130C. No mortality occurred with bluegill acclimated at 10C and subjected to a temperature differential less than or equal to 210C. Low thermal responsiveness was observed most frequently in avoidance studies conducted at acclimation temperatures less than 100C and in preference studies conducted at acclimation temperatures less than 200C