The Yoshino diversion (Yoshino Bunsui) was established to supply irrigation water from the Yoshino River to the Yamato plain. In order to examine fish introductions through the canals of the Yoshino Bunsui, the genetic structure of 17 populations of dark chub Zacco temminckii collected from the Yamato and Yoshino rivers were analyzed and their mtDNA ND2 sequences studied. A total of 16 haplotypes were detected in 261 individuals, 6 haplotypes being present in both rivers. In the Yamato River, the shared haplotypes were found to be associated with the locations of inflows from the Yoshino Bunsui. On the other hand, the majority of haplotypes found in individuals from the Yamato River were not found in those from the Yoshino River. This study confirmed the secondary introduction of dark chub from the Yoshino River into the Yamato River via the Yoshino Bunsui.
