No abstract

Chaenogobiuc isaza TANAKA, an endemic goby, is one of the important fish of Lake Biwaa and its annual catch ranks third among all fishes in that lake.

The purpose of this paper is to investigate the auditory threshold of Japanese horse mackerel which is one of the important pelagic fish for Japanese fisheries. The hearing of fish was studied by means of a cardiac conditioning technique. Classical conditioning method was performed with the sound coupled with a delayed electric shock. The threshold was determined by analyzing the electrocardiogram. The sensable frequencies ranged widely from 70Hz to 3000Hz which was most stimulative to the Japanes horse mackerel. As the frequency becomes higher than 70Hz, the auditory threshold decreased. At 1000-1500Hz(sound pressure 81-75dB) when the fish's hearing was most sensitive, the threshold tends to increase more than one. Lastly, it was assumed that a round haul netter traffic noise caused an escape action for the fish shoal.

No abstract

The differences between swimming and feeding activity of recorded underwater sound in summer and winter produced by japanese horse mackerel in a net pen were analyzed using the one-third octave band method. The small and big-sized fish show the same curve patterns under swimming and bait-eat ing activity in summer, but in the term of the maximum and minimum level frequencies, it seems slight ly different. The swimming sound curve pattern in summer was same as in winter, but there were some different patterns in bait-eating sound. The two respective records obtained simultaneously on the in side and outside of net pen when swimming activity were same in regard to the pattern and sound level, but the records when bait-eating activity were different.