Abstract
The author, using a fishing implement as shown in Fig. 1., carried the study on all of the anadromous “ayu” fry which had been caught at the mouth of the River Okumo, a small river at dawn. Out river, about 8km in length, pouring into the Japan Sea, for May 1-2, 1962. The results are as follows: 1) “Ayu” fry began to make many schools at adjacent water off the mouth of the For 9a.m. to 10a.m. some of them showed the anadromous activity, at midday, however, the activity was shown by few of them. 2) The anadromous activity were suddenly activated at about 4p.m., the peak of that was observed after the sunset when both the river water temperature and the sea water one extremely approached, and the activity gradually decreased as the night goes on. And that was never seen for 9p.m. to 3a.m. in the next morning. 3) It was found that the anadromous activity reached to the peak for 5p.m. to 8p.m., amounted to 345 in caught number of fry, three quaters of the total number (453) on the day. 4) These fry caught for 3a.m. to 9p.m. were ranged between 4.3cm and 7.8cm in body length, and between 0.5g and 3.5g in weight. And all of the fry caught for 9a.m. to 10a.m. were lager size, being over 7cm in body length, them the others.
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