Feeding habits of masu salmon (Oncorhynchus masou) in the Oh river system of northeastern Honshu, Japan
1989
Kiso, K. (Tohoku National Fisheries Research Inst., Shiogama, Miyagi (Japan)) | Kumagai, I.
The feeding habits of masu salmon were investigated with an emphasis on seasonal changes in food composition, age groups and phases (parr and smolt) in the Oh River System. 285 masu salmon (including stream resident parr) were collected between 1985 and 1988. Stomach contents were analyzed by four different methods: the number method; the weight method; the occurrence method and the index of relative importance. Masu salmon fed mainly on aquatic insects including Ephemeroptera, Trichoptera, and Diptera throughout the year. However, from spring to autumn the diversity of their food composition increased considerably, being supplemented by terrestrial insects, spiders, fish eggs and larvae, Gammaridea and Asellus sp. (Isopoda). In the summer the main food of underyearling masu salmon consisted of Chirobinudae pupae, Heptageniidae and Baetidae. On the other hand, yearling or older masu salmon fed mainly on Stenopsychidae and other Trichoptera which were larger than the organisms consumed by the underyearling group of fish. Masu salmon parr fed on large-sized animals such as Trichoptera while smolt fed on small-sized animals such as diptera during the period of seaward migration. These differences in the size of organisms that were fed upon seemed to be based on the "size hierarchy" of masu salmon
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