Cardiovascular responses of largemouth bass to exhaustive exercise and brief air exposure over a range of water temperatures

In this study we examined the effects of exhaustive exercise and brief air exposure on the cardiovascular function of largemouth bass Micropterus salmoides at four water temperatures (13, 17, 21, and 25°C). We used Doppler flow probes to monitor cardiac output and its components (i.e., stroke volume and heart rate) while we manually chased fish to exhaustion to simulate angling, exposed them to air for 30 s, and then recorded patterns of recovery. Resting cardiac variables generally increased with increasing water temperature except for stroke volume, which was temperature independent. Fish heart rate became erratic during exercise, and during air exposure fish exhibited severe bradycardia before becoming tachycardic when returned to the water. Maximal change occurred most rapidly for cardiac output (about 5 min). Several minutes later, changes in heart rate (increase) and stroke volume (decrease) simultaneously reached maximal deviations from resting values. Cardiac output and heart rate increased 150–200% relative to resting values despite 50% reductions in stroke volume, suggesting that largemouth bass are primarily frequency modulators. Maximal changes generally increased with water temperature for cardiac output and heart rate but not for stroke volume, resulting in heightened scope for cardiac output and heart rate with increasing water temperature. Recovery patterns were not influenced by water temperature. Cardiac output and heart rate generally returned to predisturbance levels in approximately 135 min, whereas stroke volume recovered more rapidly (about 110 min). Based on these findings, we suggest that largemouth bass exposed to exhaustive exercise and brief air exposure are capable of recovering from handling disturbances in several hours across the range of water temperatures that we examined (13–25°C).