Metabolic correlates of burst swimming capacity of juvenile and adult threespine stickleback (Gasterosteus aculeatus)

The relationship between burst swimming performance and muscle metabolic capacities was examined in juvenile and adult threespine sticklebacks (Gasterosteus aculeatus). The absolute burst speed measured during startle responses increased markedly with growth of juveniles, but this positive allometry did not continue in adults. The allometry of phosphofructokinase (PFK), lactate dehydrogenase, creatine phosphokinase activities and protein concentrations was positive in juveniles and became negative in adults. The lower activities in adults may reflect the mobilization of muscle proteins for reproduction. In juveniles, absolute burst swimming and muscle glycolytic capacity show a similar allometry. However, when the influence of factors such as size and age was removed by calculating residuals from multiple regressions, variation in muscle enzyme activities in juveniles did not explain variation in their swimming capacity. In adults, interindividual variation in PFK and cytochrome C oxidase activities was correlated with variation in the burst swimming capacity. Apparently, mobilization of muscle proteins in support of reproduction may lead muscle enzyme levels to limit burst performance.