SUMMARYAlthough acoustic communication is an integral part of cichlid behaviour, its mechanism has never been identified before. In the present study, a combination of approaches was used to investigate the sound-producing mechanism of Oreochromis niloticus. Synchronisation of high-speed video data (500framess Supplementary material available online at

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Abstract:The swimming movements of C. gariepinus larvae were recorded with a high-speed camera (400, 500 and 800 fps) from 0 to 336 hours post-hatching. Movements of adult fish were also recorded to provide information on the last developmental stage. Seven landmarks positioned on the fish midline were used during tail beating to determine various parameters during ontogeny and, on the basis of these parameters, to describe the first appearance of swimming movements and their development and efficiency during growth.Larvae were unable to swim at hatching (4 mm total length). Swimming movements were established at 48 hours posthatching when the fish measured between 7 and 8 mm total length and the yolk sac was more than 95% absorbed. At this stage, lateral excursion of the head appeared strongly reduced (from 13% to 6% of the total length). The efficiency of swimming movements increased throughout ontogeny, as did the homogeneity of the speed of the propulsive wave. Spontaneous swimming speed of 1 to 10 TLs -1 were observed in early stage (8-12 hPH). The various speed induced significant variations in parameters such as the amplitude of lateral head movements, swimming efficiency, and body rigidity. No major change was observed at the theoretical flow-regime transition.

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 (r 2 mean and CV of r 2 as 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.