Sound Production by Mulloway (Argyrosomus japonicus) and Variation Within Individual Calls

Abstract

Several soniferous (sound-producing) fish species can generate a number of different call types, providing significant information for intended recipients and observers. Understanding the level of variation they are capable of and whether it is voluntary or not gives an indication of how individually specific their calls might be. Similar to other Sciaenidae, mulloway (Argyrosomus japonicus) produce calls associated with spawning behaviour by vibrating their swimbladder. Dissection revealed mature mulloway have bi-lateral, highly vascularised ‘sonic’ muscles, with dorsoventrally orientated muscle fibres along the posterior two-thirds of the swimbladder, similar to French meagre (A. regius). Repetitive contraction of these muscles likely impinges on the sides of a loosely supported swimbladder, to generate motion. In the Swan River, Western Australia, mulloway produce a category of ‘long’ calls comprising 11–32 contractions at pulse repetition intervals and resulting carrier frequencies of approximately 16.6 ms and 60 Hz, respectively. However, throughout the ≈ 0.3 s calls this repetition rate may stay constant, rise, fall or a combination. In 13% of analysed calls, a pre-call pulse of lower amplitude than subsequent pulses was observed. A category of short calls (1–5 pulses) employed carrier frequencies of up to 114 Hz initially, but this decreased with each pulse, suggesting that these calls are at the limit of contraction rates of the sonic muscles. The study shows that even within previously defined call categories mulloway have the ability to produce several variations. Whether these variations are generated voluntarily or not and whether they can be perceived by the intended recipient are unknown and suggested as a topic of further work.