The mating call of the plainfin midshipman fish, Porichthys notatus

Synopsis

A previously unreported kind of fish sound, which was produced spontaneously by nesting male Porichthys notatus, was recorded in the field and laboratory. Unlike other fish sounds, this monotonous ‘hum’ continues uninterrupted from a few seconds to over 60 min with a mean length of about 11 min. It has a fundamental frequency between 98–108 Hz. The hum was produced only at night. The hum stimulates male-searching behavior in gravid females and serves as an underwater acoustic beacon for mate localization in this nocturnally active species. Gravid females responded in identical manner to pure tones as to the hum and became most highly excited at ~95 Hz, but also responed actively to pure tones over a range of 85–115 Hz. Spent females, juveniles and ripe males showed little, if any, response to the same pure tones. Gravid females tracked in an 8 m diameter concrete tank oriented to the 95 Hz pure tone by swimming directly 2–3 m to the suspended speaker, or by swimming in a circuitous path to the source, then pausing, turning or stopping under the speaker or swimming up to and butting and nipping the speaker.