Acoustic communication in triglids and other fishes
Sound production is widespread among teleosts and is usually observed in social contexts. Many fish, such as triglids, produce sounds by contracting a pair of specialised striated muscles attached to both sides of the swimbladder wall, yielding low frequency sounds made up of repeated brief pulses. Temporal features of acoustic emissions can be controlled by the rate of muscle contraction, thus providing a rich means of conveying information. In this study the sound features of the grey (Eutrigla gurnardus), the streaked (Trigloporus lastoviza), the red (Aspitrigla cuculus) and the tub (Trigla lucerna) gurnards were compared. The grey and the red gurnards emitted 3 different sound types, knocks, grunts and growls, whereas the streaked and the tub gurnards only emitted one sound type, growls and grunts respectively. Interspecific differences of calls were marked and based on the temporal patterning and on the grouping of the pulses. In the grey gurnard, ontogenetic changes in sound production were found. The sound production rate, the proportion of emitted sound type and the physical features of sound varied with fish size. A study of diel and seasonal variations of sound production in the grey gurnard showed that more sounds were uttered during the day than at night and that grunts were more important and intense during the Spring-Summer period. The sonic apparatus was examined in the species mentioned above and also in the large-scaled gurnard (Lepidotrigla cavillone) and the piper (Trigla lyra). The swimbladder and the sonic muscles grew throughout life in all species. Variations in the sonic apparatus with fish gender or time of the year were not detected. This suggests that the ability to vocalise is similar in both male and female gurnards, probably even during courtship. The shape of the swimbladder was species-specific. All species possessed a pair of intrinsic sonic muscles except for the piper whose sonic muscles were extrinsic. The pair of intrinsic sonic muscles of the grey gurnard contracted synchronously and each contraction generated a pulse of sound.