Japanese fluvial sculpin

The Japanese fluvial sculpin (Cottus pollux) is a species of freshwater ray-finned fish belonging to the family Cottidae, the typical sculpins. It is endemic to Japan, where it inhabits mountain streams in Honshu, Shikoku, and Kyushu. It reaches a maximum length of 15.0 cm (5.9 in). It is also known as the Japanese bullhead.