A record of Gymnogobius cylindricus from Lake Notoro, Abashiri, Hokkaido, northern Japan

Two specimens of Gymnogobius cylindricus (Tomiyama, 1936) were collected from Lake Notoro in Abashiri, Hokkaido, Japan. This species has previously been recorded only from brackish water tidal flats in western Japan and Korea. Collected specimens (male, 54.2 mm standard length; female, 55.5 mm standard length) represent the northernmost and easternmost records, located far from their known distribution range. Their morphological features (meristics, cephalic sensory canal pore distributions and body coloration) are consistent with those of previous specimens of the species. Genetic analysis revealed that the newly collected specimens had nearly identical mitochondrial Cytb sequences (1183bp) as those of G. cylindricus from western Japan. Our findings suggest that the species may have been dispersed by the Tsushima and Soya warm currents from western Japan to northern Hokkaido, indicating the possibility of hidden habitats along the route.