Abstract
Bitterling are fishes that use freshwater mussels for oviposition. Mussel utilization by an endangered bitterling species, Acheilognathus tabira erythropterus, and an exotic species, Rhodeus ocellatus ocellatus, both of which spawn in spring, were investigated in a lowland river. Twenty nine freshwater mussels Unio douglasiae nipponensis (Unioninae) (63% of 46 individuals examined)hosted A. t. erythropterus eggs and embryos, mainly in their inner gills. One U. d.nipponensis (2.1%) and 2 Anodonta sp. (Anodontinae) (100%) hosted R. o. ocellatus eggs and embryos. The different mussel species utilized by the two bitterling may be important for their continued coexistence.
