The taxonomic status between two Japanese cyprinids, Phoxinus lagowskii steindachneri and P. oxycephalus jouyi has been quite vague because of their resemblance of outer features to each other. The two forms from the four sympatric rivers were inspected to confirm the relationships between both as dis-tinct biological species on the basis of biochemical and morphological analyses. As a result they could be completely divided into two distinct groups in genetic and morphological characters, which taxonomically match P. lagowskii stein-dachneri and P. oxycephalus jouyi, respectively. The present study suggested the presence of reproductive isolation between the two species, and revealed that large local variation and secondary sexual characters in each species had contributed to taxonomic confusion.
