Production de sons chez le baliste Picasso Rhinecanthus aculeatus (Linnæus, 1758)

Although the sound production of Rhinecanthus aculeatus (Linnaeus, 1758) is known since 1889, its mechanism and the associated behavioural context have never been studied. The goals of this study are (1) to describe the sound(s) produced by R. aculeatus; (2) to examine the possible link between the fish length and the characteristics of the sound(s) produced; (3) to describe the mechanism(s) involved in the sound production and (4) to study the behavioural context of the sound production. The fish have been recorded holding in hand underwater with a hydrophone HTI-96-MIN and a recorder TASCAM DR-07. Two different sounds have been recorded. The first one was 83 ± 22 ms long with a dominant frequency of 191 ± 42 Hz. The second one was 59 ± 31 ms long with a dominant frequency of 1616 ± 531 Hz. The effect of the fish length on the frequency has been demonstrated for both sounds. The morphological examinations and the use of a high speed video camera have shown that the first sound was produced during the friction of the pectoral spine against modified scales called scutes. The role of the pectoral fin is to push sharply the scutes whose configuration change would be the cause of the sound production. It is the alternation of movements of the left and the right fins that would allow the production of an extended sound. The second sound would be a stridulation sound produced by the pharyngeal teeth. Finally, the behavioural examination in the natural environment has shown that the first sound was heard in a stress situation and probably when the female defends its nest, while the second one was mainly heard during the alimentation.