Effects of thermal increase on aerobic capacity and swim performance in a tropical inland fish

Rising water temperature associated with climate change is increasingly recognized as a potential stressor for aquatic organisms, particularly for tropical ectotherms that are predicted to have narrow thermal windows relative to temperate ectotherms. We used intermittent flow resting and swimming respirometry to test for effects of temperature increase on aerobic capacity and swim performance in the widespread African cichlid Pseudocrenilabrus multicolor victoriae, acclimated for a week to a range of temperatures (2 °C increments) between 24 and 34 °C. Standard metabolic rate (SMR) increased between 24 and 32 °C, but fell sharply at 34 °C, suggesting either an acclimatory reorganization of metabolism or metabolic rate depression. Maximum metabolic rate (MMR) was elevated at 28 and 30 °C relative to 24 °C. Aerobic scope (AS) increased between 24 and 28 °C, then declined to a level comparable to 24 °C, but increased dramatically 34 °C, the latter driven by the drop in SMR in the warmest treatment. Critical swim speed (Ucrit) was highest at intermediate temperature treatments, and was positively related to AS between 24 and 32 °C; however, at 34 °C, the increase in AS did not correspond to an increase in Ucrit, suggesting a performance cost at the highest temperature.