Thermal Optima and Tolerance in the Eurythermic Goldfish (Carassius auratus): Relationships between Whole-Animal Aerobic Capacity and Maximum Heart Rate

The wide thermal tolerance range of a eurythermic fish (goldfish, Carassius auratus) was used to evaluate how temperature performance curves derived from maximum heart rate (f(H)) related to those for aerobic scope. For acclimation temperatures of 12 degrees, 20 degrees, and 28 degrees C, optimum temperatures derived from aerobic scope curves (T opt) were 19.9 degrees +/- 0.4 degrees, 19.3 degrees +/- 0.8 degrees, and 28.7 degrees +/- 0.8 degrees C, respectively. The Arrhenius breakpoint temperatures (T-AB) for maximum f(H) were 21.5 degrees +/- 0.6 degrees, 23.8 degrees +/- 0.9 degrees, and 24.6 degrees +/- 0.5 degrees C, respectively. The T-QB (temperature where the incremental Q 10 of maximum f(H) decreased abruptly below 1.9) was 24.0 degrees +/- 0.7 degrees and 29.8 degrees +/- 0.6 degrees C for the 12 degrees and 28 degrees C acclimation temperatures, respectively, and was within the T opt window (11.5 degrees - 30.3 degrees and 26.9 degrees - 30.5 degrees C, respectively), but T-QB for the 20 degrees C acclimation temperature (27.3 degrees +/- 0.6 degrees C) was higher than the T opt window (15.4 degrees - 23.2 degrees C). Warm acclimation increased the upper critical temperature (T-crit; from 37.2 degrees +/- 0.7 degrees to 44.7 degrees +/- 11.8 degrees C) as well as the temperature that triggered a cardiac arrhythmia (T-arr; from 31.1 degrees +/- 0.7 degrees to 39.3 degrees +/- 0.4 degrees C). In conclusion, we propose that maximum f(H) and its associated rate transition temperatures (T-AB, T-QB, and T-arr) can be used to estimate the upper thermal tolerance of eurythermic as well as stenothermic fish independent of acclimation temperature. All the same, great care is needed with such evaluations. For the goldfish, while T-AB and T-QB were always within the T opt window for 90% of maximum aerobic scope and T opt was closely associated with T-AB for 12 degrees C-acclimated fish, T-QB had the closest association after 28 degrees C acclimation, and both T-AB and T-QB were above the T-opt window after 20 degrees C acclimation.