Can Lactate Dehydrogenase be used to Index Anaerobic Activity in Fishes?

Anaerobic activities such as those associated with spawning, foraging for prey, and predator avoidance are difficult to quantify in wild fish. This study experimentally evaluated if the muscle enzyme lactate dehydrogenase (LDH) can be used to index recent anaerobic activity in fish by testing the hypothesis that muscle LDH activity will be greater in exercised fish than in rested fish. We used burst swimming motions in a swim tunnel to elicit anaerobic metabolism in a 5 day anaerobic exercise treatment (n = 30) and a rested control group (n = 30). On average the exercised fish produced significantly more LDH in their muscle tissue (average = 19.5 IU/ug, SE = 1.8, F = 12.88, df = 2, 57, P < 0.001) due to the increased anaerobic activity than rested fish (average = 13.4 IU/ug, SE = 0.9). However, large individual variability in LDH activity within groups resulted in some overlap between treatment groups. Therefore we suggest limiting the use of LDH activity to infer relative comparisons of anaerobic activity among groups until the relationship is more clearly understood.