Critical and Chronic Thermal Maxima of Northern and Florida Largemouth Bass and Their Reciprocal F1 and F2 Hybrids

Abstract Thermal responses varied among four genetic stocks of juvenile largemouth bass: northern largemouth bass Micropterus salmoides salmoides (NLMB), Florida largemouth bass M. s. floridanus (FLMB), and both reciprocal F1 hybrids, NLMB ♀ x FLMB ♂ (N x F) and FLMB ♀ x NLMB ♂ (F x N). Thermal responses for each stock were measured as the critical thermal maximum, the temperature at which death occurred during a temperature increase of 0.2°C/min, for fish at various acclimation temperatures (8, 16, 24, 32°C); and chronic thermal maximum, the temperature at which death occurred during a temperature increase of 1°C/d, for fish acclimated to 32°C. The rank order of values for both response measurements was identical for the four stocks: F x N > FLMB > N x F > NLMB. Increased acclimation temperature resulted in significant, proportional increases in the critical thermal maxima for all stocks. In addition, second-generation hybrid stocks (N x F F2 and F x N F2) that were acclimated at 24°C produced similar cr...