Figure 3.

Maximum heart rate (f_Hmax) and critical thermal maximum (CT_max) in response to acute warming of PFRC H-strain rainbow trout (O. mykiss) as a function of acclimation temperature. (A) Mean f_Hmax for each acclimation temperature group during acute warming (n = 12). Acclimation temperatures were 15°C (), 17°C (), 19°C (), 21°C (), 23°C () and 25°C (). Data points are connected by a solid line provided all fish in an acclimation group retained a rhythmic heartbeat at that temperature. If not a broken line connects the average f_Hmax for the fish the still retained a rhythmic heartbeat, with the percentage count remaining indicated in the inset. All individual fish had developed an arrhythmic heartbeat by 31°C and by 28°C for those at the two coldest acclimation temperatures. (B) Temperature at which each acclimation group reached its CT_max (n = 10), cardiac arrhythmia temperature (T_arr) and maximum f_Hmax (T_peak). Amber area labels the difference between whole-organism and tissue thermal tolerance and the differences between CT_max and T_arr at 15°C, 23°C and 25°C acclimation temperature are denoted. Two-way ANOVA performed indicates T_arr is significantly different from CT_max (F = 213.2, P < 0.0001). (C) Peak f_Hmax reached at each acclimation temperature (n = 12). All values are presented as means ± sem, except right y-axis in (A) presented as count in %. (sem may be hidden by the symbol). Dissimilar letters represent statistically significant differences among mean values for that variable.