Ontogeny of swimming movements in bronze corydoras (Corydoras aeneus)

Fish larvae experience fundamental morphological, physiological, and physical changes from hatching to adulthood. All of these changes have an effect on the locomotor movements observed in the larvae. We describe the development of swimming movements in larval bronze corydoras ( Corydoras aeneus (Gill, 1858); Ostariophysi, Siluriformes) during their ontogeny. Swimming movements of adults and larvae, aged 0–512 h posthatching, were recorded at 500 frames/s. Movements were analyzed by digitizing points along the fish midline. Movements are described by direct (swimming speed and amplitude of landmarks) and indirect (r2meanand CV of r2as movement coordination indices; Strouhal number as an efficiency index) parameters. The increase in swimming speed correlated with improvement of movement coordination in both larvae and adults, as well as with an increase in swimming efficiency in larvae. Directly after hatching, swimming movements were coordinated but were not efficient. Efficiency increased rapidly with fish growth up to 8 mm total fish length and disappearance of the yolk sac. These events were coupled with reduction of the maximal lateral amplitude observed along the whole body during swimming. The anguilliform swimming mode was used at hatching, but a transition to the carangiform mode was observed at approximately 17 mm total fish length.