Hybridization between two bitterling fish species in their sympatric range and a river where one species is native and the other is introduced.

The distributions of two bitterling fish (subfamily: Acheilognathinae), Tanakia lanceolata and T. limbata, overlap in western Japan. Acheilognathinae fish lay their eggs in the gills of freshwater bivalves, and the early juvenile stage develops in the gills.