This study provided a first detailed description of the acoustic calls and the possible sound production mechanism in the Giant Sea Bass (Stereolepis gigas). Passive acoustic (hydrophone) recordings of Giant Sea Bass sounds were made of three mature individuals (40–45 kg) held in a circular 17,000 l seawater tank isolated from other fish species. Four basic sounds plus combinations were identified from the tank recordings when fish were present and were encountered on numerous occasions throughout the study. We classified the basic sounds as two types of pulses (A and B), short bursts, and long bursts, and combinations of short and long bursts. Mean peak frequencies of the four sound types were less than 39 Hz, while mean durations ranged from 67 ms to 545 ms, depending on sound type. We also obtained and dissected two mature, adult Giant Sea Bass to describe the morphology of a putative sound production mechanism. Five putative sonic muscles were discovered between each of the first six pleural ribs of the male examined. These five massive muscles (=obliquus superioris?) unite ribs 3 to 9 and were found at the level of the deep hypaxial musculature. The identification of these sounds and accompanying sonic mechanism marks the first occurrence of sound production in the family of wreckfishes (Polyprionidae). This knowledge of the acoustic characteristics increases our ability to document the presence, activity, and possibly the abundance of this critically endangered species at spawning sites.

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