Occurrence of Myxobolus arcticus and M. neurobius (Myxozoa: Myxosporea) in Masu Salmon Oncorhynchus masou from Northern Japan

Abstract

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.