Thermal Tolerance of Fathead Minnows {Pimephales promelas) in Response to Acute Heatwaves

Abstract

Heatwaves are expected to increase in frequency and magnitude in response to anthropogenic climate change. The long-term outcomes of how organisms will respond to heatwaves remains unclear, with evidence suggesting that there may be beneficial and detrimental effects. We tested how fathead minnows (Pimephales promelas) at a late-life stage respond to heatwaves of varying duration. In addition, we tested whether acclimation temperature (25°C and 28.5°C) played a role in modifying their critical thermal tolerance values (CTmax) to heatwaves. We found that fish acclimated to 25°C had higher CTmax values when exposed to a heatwave than the controls. However, this was not the case for 28.5°C-acclimated fish that were exposed to a 1-d early-life or 1-d late-life stage heatwave. On the contrary, the acute thermal stress in both the 25°C- and 28.5°C-acclimated groups did not alter post-heatwave growth or food consumption. For some traits and under some acclimation temperatures, therefore, this study demonstrates beneficial carry over effects. We suggest that the adaptability of fathead minnow CTmax in response to heatwaves may allow for this species to overcome the effects of extreme heatwaves in the future.