First highlight of sound production in the glassy sweeper Pempheris schomburgkii (Pempheridae)

Many sounds produced by fishes remain to be described. Understanding sound production for vocal species would permit the development of passive acoustic monitoring of fish diversity. The present study investigated sound production in the glassy sweeper Pempheris schomburgkii in Guadeloupe reefs, French West Indies. Two recording approaches were used: passive acoustic monitoring in the wild and active recordings with hand-held individuals in captivity. Calls consisted of series of harmonic pop sounds with a dominant frequency of 360 Hz. On coral reefs, they were produced in chorus, starting after sunset and lasting up to 3 h. Sounds recorded in situ were longer with more pulses than sounds recorded from captive specimens. These differences in temporal features suggest two types of sounds: acoustic signals that act as distress calls and those that might be involved in group-level activities such as group cohesion and reproduction. A morphological study was also performed to describe the anatomy of the sound production apparatus which consisted of a pair of large sonic muscles which inserted dorsally on a contractible anterior part of the swim bladder. Contractions of these muscles extend rostrally this part of the swim bladder while an inner sheet of elastic connective tissue acts as a recoiling system to help the swim bladder recover its initial position during relaxation of the sonic muscles. The present results, therefore, contribute to the description of sound production by fishes found in an underexplored region and further illustrate how passive acoustics may be used to monitor fish populations in the future.