Positive Effects of Fast Growth on Locomotor Performance in Pelagic Fish Juveniles: In Contrast to Existing Evidence
Abstract Many laboratory experiments on aquatic vertebrates that inhabit closed water or coastal areas have highlighted negative effects of fast growth on swimming performance. Nonetheless, field studies on pelagic fishes have provided evidence of survival advantages of faster growing individuals. To reconcile this contradiction, we examined the relationship between growth rate and swimming performance as a continuous function for juveniles of chub mackerel (scomber japonicus) using 3D tracking analysis. For experiments, 20, 24, 27 and 30 days-post-hatch individuals within the size range of 14.5–25.3 mm were used. We found that the growth–swimming (burst speed) relationship in chub mackerel was substantially positive and it was suggested to be supported by morphological traits such as muscle area, which also positively correlated with growth rate. This finding is consistent with field observations showing selective survival of fast-growing individuals of this species, reconciling the current contradiction between laboratory experiments and field observations. Growth was suggested to trade off with swimming performance, as reported in many previous studies, when it was extremely fast. Therefore, a dome-shaped quadratic curve described the relationship between growth rate and burst speed better than a linear or generalized linear model. These results, obtained from the rarely tested offshore species, strongly suggests the importance of experimental verification using animals that inhabit various types of habitats in understanding the principles underlying the evolution of growth–locomotor relationship.