Using mitochondrial DNA cytochrome b region nucleotide sequences, we investigated the phylogeographical structure of Tanakia lanceolata, which inhabits the Tokai region of central Honshu, Japan. As a result, we found one non-native haplotype (native distribution in the Kinki region) and 32 native haplotypes in the Tokai region. The non-native haplotype was only found in the Shin River system in Aichi Prefecture. Therefore, it is suggested that artificial introduction from other regions is limited. Among the haplotypes included in the native lineage, one haplotype was widely distributed in the Tokai region, while 31 haplotypes were endemic to one river system or neighboring river systems. The analysis of molecular variance (AMOVA) showed genetic differentiation between river systems. We propose to consider each river system as conservation units.
