Acoustical Behavior of the Menpachi, Myripristis berndti, in Hawaii

Abstract

The menpachi (Myripristis berndti) is found in aggregations inside caves and under ledges during the day in water more than 3 m deep. Diel tape recordings in these areas showed that the fish produced four types of sounds (knocks, growls, grunts, and staccatos), with no crepuscular peaks, from dawn to dusk. At night, when the fish scattered to feed, few sounds were detected. A fifth sound was produced when fish were hand-held. The sound-producing mechanism was determined by a series of ablation experiments on hand-held fish. It consisted of a pair of bilateral muscles attached to the skull anteriorly and the air bladder, the first two dorsal ribs, and the cleithrum bone posteriorly. Populations of 6-7 fish were maintained in the laboratory in large tanks with an artificial cave. They remained inside the cave during the day but swam actively throughout the tank at night. Brief chasing of a small fish by a larger, accompanied by knocking sounds, was frequently observed. Growl sounds were produced during more intense aggressive interactions between two fish of about the same size. There was no evidence of territoriality by members of any population. Few grunt or staccato sounds were produced when various species of nonpredatory fish were introduced among laboratory populations. Many of these sounds were elicited when moray eels were introduced. Sound playbacks to four populations from one of two speakers on either side of the cave elicited different responses depending on the sound tested. All fish immediately turned to and moved toward the experimental speaker when grunt or staccato sounds were played. Some fish briefly turned to the experimental speaker when knocks were emitted but none moved to the source. There was no detectable change in behavior when background noise was played back. Three fish tested in an aktograph showed increases in locomotory activity at night which corresponded with periods of nocturnal scattering and feeding in field populations. The acoustical system of the menpachi is compared with that of the longspine squirrelfish, Holocentrus rufus , an Atlantic species.