Studies on the Underwater Sound-VII

The underwater calls of the Japanese marine drum fishes, Koichi (Nibea albiflora) and Shiroguchi (Argyrosomus argentatus), living in Ariake Sound have been studied. The underwater calls of these fishes are a grating sound consisting of a train of pulses. The call was higher in Koichi than in Shiroguchi and in males than in females. The calls are produced by cramping the drumming muscle against the body axis and by rubbing this muscle with the peritoneum. The call produced is resonated and amplified by the swim-bladder connected with the drumming muscle before it is emitted into the sea water. These marine drum fishes live in Ariake Sound throughout the year. The chorus could be heard from early May to the middle of September and the sound-production was connected with the reproduction of these species. The most noisy period was, however, July and August following the spawning peak. These fishes began to emit their calls before sunset and the sound level of the chorus attained its maximum after sunset. No calls were heard from mindnight to noon. The duration of the chorus attained its maximum in August and gradually decreased again thereafter. It was in no way related to tide.