Limnotrachelobdella okae (Hirudinida: Piscicolidae) Parasitic on Big-scaled Redfin, Pseudaspius hakonensis (Cypriniformes: Leuciscidae), in Two Brackish Water Lakes, Hokkaido, Japan

Specimens of the coastal marine fish leech Limnotrachelobdella okae (Moore, 1924) were collected from the pelvic fins and lateral body surface of big-scaled redfin, Pseudaspius hakonensis (Günther, 1877), in two brackish water lakes, Lake Tofutsu and Lake Abashiri, on the Sea of Okhotsk coast, Hokkaido, northern Japan. The external morphology of the specimens is briefly described, and the two lakes represent new locality records for the leech. Similarly to coastal marine waters, inshore brackish water lakes are suggested to be a habitat in which L. okae can complete its life cycle. Seasonal occurrence of the species may differ between subarctic Hokkaido and three temperate regions of Japan (Honshu, Shikoku, and Kyushu). The role of big-scaled redfin and its congener, Pacific redfin, Pseudaspius brandtii (Dybowski, 1872), in transporting L. okae alive from the coastal sea to brackish and fresh water bodies is discussed in terms of their diadromous migration ecology.