胃の内容物から見たブリの食性-II : 摂餌活動の日週変化および成長に伴う摂餌率の変化

概要

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In the present paper the author has quantitatively analysed the feeding habits of the yellowtail, Seriola quinqueradiata T. & S., particularly the daily change of the feeding activity and the feeding amount varying with growth, based on the stomach contents of the 262 individuals caught in Wakasa Bay, the Japan Sea, during the period from December of 1956 to January of 58. The results obtained are as follows: 1) The fish caught in the morning has more contents in the stomach than that caught in the evening. Accordingly, we may safely say that the fish has a voracious feeding activity at dawn, and has less in the daytime. The food taken by the fish in the morning may have been digested by the evening (Table 1). 2) The rate of feeding (food weight/body weight×100) falls with varying degrees as the fish grows in the first rapidly and then gradually as shown in Fig. 1. Hence, we can presume that younger fish will become more vigorous tnan older ones for their digestion. Consequently, younger fish must be able to migrate throughout the wide region between the northern and southern areas of the Japanese waters, while older ones become so dull and slack in their activity that some of them are apt to settle within a relatively limited area. What is called “a bank shoal” may be formed in this way.