The Sound-Producing Mechanism of the Croaking Gourami, Trichopsis vittatus (Pisces, Belontiidae)

Abstract

In Trichopsis vittatus, two independent bilateral muscles inserting on separate suprabranchial organs displace these organs and set the air-filled suprabranchial cavities surrounding each organ into vibration to produce the characteristic croaking sound. Histological examination shows the fibers of the sonic muscles to be about one-third the diameter of dorsal body wall muscle fibers. Severing one of the bilateral muscles results in the elimination of alternate tone bursts in sounds recorded afterward. Similarly, puncturing one of the suprabranchial cavities results in sounds in which alternate tone bursts have a drastically reduced intensity. These results indicate that the pulses of sound in each tone burst are produced by a series of contractions of one bilateral muscle and that this series of contractions alternates with a series of contractions produced by the bilateral muscle on the other side. The swim bladder, in turn, amplifies the sounds produced by both suprabranchial cavities. Filling the swim bladder with water results in sounds in which all tone bursts have a reduced intensity. The posterior air-filled body cavity, on the other hand, does not play a significant role in sound production.