Auditory threshold of marbled sole Pleuronectes yokohamae

The auditory thresholds for 10 specimens of the marbled sole Pleuronectes yokohamae were determined by heartbeat conditioning using pure tone stimuli of 9 frequencies from 60 to 1, 000Hz, which were coupled with an electric shock. The marbled sole could hear sound in the frequency range from 60 to 1, 000Hz, and the lowest threshold was 92.5dB re 1μPa at 100Hz. Hearing ability declined rapidly with increasing frequency above 300Hz, but little difference occurred in hearing ability between 400 and 500Hz. The results show that the auditory thresholds of marbled sole are higher and its sensitive frequency range is narrower than that for fish that have swimbladder.