As a part of a marine ranching project, this study examined responses to tone-bursts of different frequencies by flounder juveniles which had been conditioned to come to a sound source of 300Hz tone-bursts in a fish cage. After completion of conditioning, the flounders showed the conditioned responses to 1s tone-bursts of frequencies of 200-800Hz with a peak sensitivity at 300Hz, and a slight and short response to a continuous sound of 300Hz immediately after the sound projection, coinciding with the previous finding with res sea bream juveniles. The bimodal pattern of sound frequency-pressure threshold concluded that this conditioned response was mediated by the inner ear in response to particle displacement. This pattern, however, was different from a reported audiogram with a peak seak sensitivity at 100Hz, probably because of the effect of frequency of the conditioned sound.
