瀬戸内海東部海域におけるマダイの食性とその季節変化

概要

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The feeding habit of red sea bream, Pagrus major, was examined by stomach content analysis with special reference to its seasonal changes in Tomogashima Channel waters, an important habitat in the eastern Seto Inland Sea. The fish fed through its life on many kinds of organisms, but intensively on a few kinds of them during the feeding season from spring to autumn. It was noted here that juveniles fed on zooplankton such as Acartia omorii and Oikopleura sp. from June to July, and youngs on the pasiphaeid shrimps Leptochela from August onward. These shrimps were in fact the main prey for the fish of age 1 and over. The stomach contents were poor and changed after November, because of the fall in water temperature and the increase in its population density with overwintering assemblage. Consequently, until March, or the end of the overwintering season, fish growth was retarded with a continuous decrease in the condition factor. The change in feeding habit with the winter assemblage was most remarkable for age 0 fish. The winter season would appear to be a critical period for the survival of the fish especially at this age.