THE AUDITORY THRESHOLD OF THE BASTARD HAL IBUT PARALICHTHYS-OLIVACEUS

Using a classical respiratory conditioning technique, the hearing abil ity of the bastard halibut Paralichthys olivaceus was measured for 7 f ish at 7 frequency points between 70 Hz and 500 Hz. The conditioning r esponse was measured as suppression in the respiratory activity by the piezoelectric sensor fitted on a gill cover in a quiet water tank. Th e bastard halibut was sensitive to sounds in the frequency range from 70 Hz to 500 Hz. The auditory thresholds were observed among the 7 fis h with much difference (about 17 dB) at 100 Hz and 300 Hz. But the aud iogram had common characteristics that they had the lowest threshold a t about 100 Hz and that the threshold increased rapidly with frequency of sound between 200 Hz and 400 Hz. An attempt was also made examine the escape response of each of the above 7 bastard halibut by the soun d stimulus, but no conditioned escape response was observed after 7 ti mes applying training stimulus.