Anaerobic Swimming Metabolism of Fish: Sit-and-Wait versus Active Forager

The potential for generating energy during swimming via anaerobic metabolism and the ability to recover from exhaustive activity were examined in an actively foraging (creek chub, Semotilus atromaculatus) and a characteristically sit-and-wait species of fish (mudminnow, Umbra limi). The anaerobic threshold, as measured by a rise in muscle lactate, occurred at a higher swimming speed for the creek chub (~ 5 body lengths s⁻¹) than for the mudminnow (~2.0 body lengths s⁻¹). Anaerobic scope, defined as the rate of muscle-lactate production during maximal sprint activity, was 87% higher for the mudminnow (5.84 μmol g⁻¹ min⁻¹) than for the creek chub (3.13 μmol g⁻¹ min⁻¹). Whole-body anaerobic capacity at exhaustion (4 min) was also greater for mudminnows (9.82 μmol g⁻¹) than for creek chubs (6.46 μmol g⁻¹). The rate constant for muscle-lactate disappearance following exhaustion, however, was slightly higher for creek chubs (-0.63) than for mudminnows (-0.40). The time required for muscle-lactate concentration to return to resting values in these 1-2-g fish (4-6 h) was much less than previously reported times for large fish. Muscle-glucose concentration during recovery from 8 min of exhaustive activity was relatively unchanged in the creek chub but increased threefold in the mudminnow. The rate of increase in muscle-glycogen concentration following exhaustive activity was approximately sixfold higher for the mudminnow (23.6 mg [100 g]⁻¹ h⁻¹) than for the creek chub (3.7 mg [100 g]⁻¹ h⁻¹). Estimates of the time required for complete glycogen restoration were 6 h and 14 h for the mudminnow and creek chub, respectively. These results suggest that increased potential for and reliance on anaerobic energy production during swimming is characteristic of sit-and-wait foraging behavior in fish.