Recently, the measurements of auditory thresholds of fish that used changing heart beat rate, have been performed for many kinds of fish in Japan. But almost all of them were reported in adult fish, and did not examine the hearing ability of young fish. Juvenile fish are mainly released, but it is not clear that they have the same hearing ability as adult fish. For that reason we aimed to make clear the auditory threshold of the 0 to 2-year-old red sea bream Pagrus major.
For conditioning a 1sec pure tone sound followed by a 1sec electric shock (5 V AC) were used. When the heart beat interval was more lengthy before the sound emission, we decided the auditory threshold.
The audiograms of 0 to 2-year-old red sea bream were V shaped. Most sensitive frequencies were 300 Hz for the 0- and 1-year-old fish, and 200 Hz for the 2-year-old fish. The minimum thresholds were 92.4 dB, 83.0 dB and 71.3 dB for the 0-, 1- and 2-year-old fish, respectively. As they grew, the threshold in lower frequencies between 100 to 200 Hz was significantly decreased. It is considered that hearing sensivitity of red sea bream improves as they grow from juvenile to adult.