Positive effects of fast growth on locomotor performance in pelagic fish juveniles

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 supported by morphological traits such
as muscle area, which were also positively related 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. A
dome-shaped quadratic curve described the relationship between growth rate
and burst speed better than a linear or cubic function, suggesting that
growth may trade off with swimming performance, as reported in many
previous studies, when it is extremely fast. 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.