| Summary: | Adult masu salmon (Oncorhynchus masou) from seven rivers in Hokkaido and northern Honshu were examined for the geographical distribution of Myxobolus arcticus and M. neurobius in northern Japan. Maturing masu salmon from Japanese coastal waters of the Okhotsk Sea, Japan Sea, and western North Pacific Ocean were also studied for the prevalence of these myxosporeans. Myxobolus arcticus occurred mainly on the Japan Sea coast of Honshu, whereas M. neurobius was found in Hokkaido along the coasts of the Okhotsk Sea and Japan Sea. Sea-caught masu salmon showed various degrees of infections with M. arcticus and M. neurobius. This indicates that masu salmon migrating in Japanese coastal waters are a complex of mixed stocks that originate in various rivers. Prevalence data support the recently proposed autumn migration route of maturing masu salmon from the Okhotsk Sea to Japan Sea. 北海道および本州北部の7河川に回帰したサクラマス親魚とオホーツク海, 日本海および北太平洋の日本沿岸を回遊するサクラマスにおける粘液胞子虫Myxobolus arcticusとM. neurobiusの寄生率を調べた. Myxobolus arcticusは主に本州の日本海沿岸河川に分布したが, M. neurobiusは北海道のオホーツク海と日本海沿岸河川のサクラマスに多かった. 海洋で漁獲されたサクラマスにおける両種の寄生率は多様であり, 日本沿岸を回遊するサクラマスは様々な河川を起源とする混合群により構成されると推定された. 海洋でのこれら粘液胞子虫類2種の地理的および季節的出現傾向は, サクラマスが秋期にオホーツク海から日本海へ南下移動するという仮説を裏付けている.
|
|---|