Freshwater sculpin dwelling in Lake Chuzenji, Nikko, Kanto District, Japan, is identified as Utsusemikajika, Cottus reinii, unintentionally introduced from Lake Biwa

Freshwater sculpin dwelling in Lake Chuzenji, Nikko, Kanto District, Japan, was identified as the lacustrine type of Cottus reinii, Utsusemikajika, by using a combination of pectoral fin ray counts (15–17, mode 16), mitochondrial DNA variations and egg size (1.33 ± 0.06 mm). We suppose that C. reinii in Lake Chuzenji was introduced unintentionally from Lake Biwa along with either Oncorhynchus masou subsp. or Sarcocheilichthys variegatus microoculus during the late nineteenth to early twentieth centuries. This is the first report of an establishment of the lacustrine type of C. reinii outside of Lake Biwa.