Sound production of the Picasso Triggerfish Rhinecanthus aculeatus (Linnaeus, 1758): first case of buckling mechanism.

Sound production of Rhinecanthus aculeatus (Linnaeus, 1758) is known since 1889 but its sound producing mechanism remains poorly studied. Consequently, the goal of this study was to use a multidisciplinary approach to understand how the sounds are produced. Hand-held fish were first recorded with a hydrophone HTI-96-MIN and a recorder TASCAM DR-07. Sounds were 83 ± 22 ms (nfish = 9, nsounds = 90) long with a dominant frequency of 191 ± 42 Hz (nfish = 9, nsounds = 90). Morphological studies (dissections and µCT scans), sound analysis, different experimental manipulations (immobilisation of the pectoral fins and swim bladder filling) and the use of a high speed video camera allowed to propose a mechanism. Sounds are produced during alternate movements of the left and right pectoral fins. As soon as the pectoral fin spine touches the scales covering the lateral expansions of the swim bladder, these bony plates buckle suddenly creating a first peak. Back movements of the scales to the resting position provokes the second peak.