Effects of training on respiratory gas exchange, nitrogenous waste excretion, and fuel usage during aerobic swimming in juvenile rainbow trout (Oncorhynchus mykiss)

Abstract

Fuel utilization during aerobic exercise was determined in juvenile rainbow trout that had previously undergone 2 weeks of continuous aerobic training at 25% of their maximum sustainable speed (Ucrit) and was compared with that in untrained trout. Instantaneous fuel usage was calculated from simultaneous measurements of oxygen consumption ( MO2), carbon dioxide excretion ( MCO2), and nitrogenous waste excretion (MN). Over 58 h of sustained aerobic exercise at 55% of Ucrit, MO2and MCO2remained virtually constant in the trained fish, in contrast to the significant fall over time in untrained fish, but total gas exchange was similar in the two groups. Aerobic respiratory quotient remained constant in the two treatments. MNwas lower in the trained fish, resulting in a much lower (and stable) nitrogen quotient; the nitrogen quotient increased with swimming duration in the untrained fish. Lipid was the major fuel source powering aerobic exercise in both groups. Carbohydrate also played a significant role, whereas protein was of lowest quantitative importance. Training resulted in a decrease in reliance on protein and an increase in reliance on lipid metabolism. The role of protein oxidation in supporting aerobic swimming in fish, which is smaller than commonly believed, is further reduced by training.