Ontogeny of routine swimming activity and performance in zebra danios (Teleostei: Cyprinidae)

Zebra danios, Danio rerio, 3–39 mm long, were studied to quantify ontogenetic changes in routine (spontaneous) swimming. Swimming speeds and mean acceleration rate increased during the larval period with the most rapid changes occurring when fish were between 5 and 15 mm long. At larger sizes, the rate of increase in performance was small. This pattern presumably resulted from morphological changes which also proceeded rapidly in larvae and levelled off towards adulthood. Swimming bouts began with either a large (105°) or a small (3°) turn. Turning angle changed with size apparently due to hydrodynamic conditions, as indexed by Reynolds numbers ( Re). Larvae spent 98% of the time in the viscous and intermediate hydrodynamic regimes, of which 90% occurred at an Re of less than 110, and 23% was in the viscous regime ( Re