Abstract
Phylogenetic relationships among 4 major geographic population groups (San-in-Biwa-Ise, East Seto, West Seto and West Kyushu) of Japanese freshwater goby Odontobutis obscura (Perciformes: Gobioidei: Odontobutidae) and related species O. hikimius were inferred from partial nucleotide sequences of the mitochondrial 12S and 16S rRNA genes. The resultant mitochondrial DNA (mtDNA) phylogeny was consistent with that based on the previous allozyme analysis. This phylogeny showed that specimens from the Sagami River system in Kanagawa Prefecture, Kanto District, were extremely close to fish from the West Seto group, suggesting the formers to have been descended from individuals artifi-cially introduced from the range of the latters. Judging from the fact that about 40 individuals of the goby were easily collected by a person in 2 hrs, the Kanto popu-lation did not seem to be small, and thus might be disturbing the native fauna in the river system.
