木曽川上流域の王滝川で再発見された魚類寄生虫ヤマメナガクビムシ Salmincola californiensisと宿主の同定

長野県の木曽川上流域にある王滝川は，ヤマメナガクビムシSalmincola californiensis のアジアにおける分布南限地であるとともに，本種の異名であるSalmincola yamameのタイプ産地である．今回，王滝川本流と3支流（上黒沢，西野川，中沢川）でアマゴとヤマトイワナを採集し，本種の寄生状況を調べたところ，上黒沢で得たアマゴに本種の寄生を認めた．これは王滝川における本種の64年ぶりの再発見である．ヤマトイワナに本種の寄生は見られなかった．Salmincola yamameの記載時にヤマメと報告された宿主名は誤りで，正しくはアマゴであることを示した．The Ôtaki River, a tributary of the upper Kiso River in central Japan, is the type locality of Salmincola yamame, a junior synonym of Salmincola californiensis, and is the southernmost locality of the species in Asia. A survey on the occurrence of S. californiensis parasitic on landlocked salmonids was conducted in the main stream and three tributaries (Kami-Kurosawa Stream, Nishino River, and Nakazawa River) of the Ôtaki River in June 2017. Female specimens of S. californiensis were collected from amago Oncorhynchus masou ishikawae in the Kami-Kurosawa Stream. This represents a rediscovery of Salmincola californiensis from the Ôtaki River. Yamato charr Salvelinus leucomaenis japonicus were not infected. The host species in the original description of S. yamame was misidentified as “yamame, a landlocked form of Oncorhynchus masou” and should be corrected as amago O. masou ishikawae