Salinity tolerance of six adults ( Inversiunio jokohamensis , Hyriopsis schlegeli , Pronodularia japanensis , Cristaria plicata , Cristaria tenuis , and Sinanodonta sp.) and two glochidia ( Cristaria plicata and Cristaria tenuis ) of unionid mussels

The salinity tolerance of freshwater unionid mussels species Inversiunio jokohamensis, Hyriopsis schlegeli, Pronodularia japanensis, Cristaria plicata, C. tenuis , and Sinanodonta sp. reared in tanks was investigated. For adult mussels, the water in the tanks was adjusted to various brackish water salinity levels ( 3, 6, 10, and 12 psu ) . All adult individuals of I. jokohamensis died at salinities above 6 psu. When the salinity was gradually raised from 3-6 to 6-8 psu, almost all adult individuals of I. jokohamensis, H. schlegeli, C. tenuis , and Sinanodonta sp. died, but those of P. japanensis and C. plicata survived. When the salinity was raised from 8 to 10 psu, all adult individuals died. On the other hand, when the salinity levels in tanks were raised from 0-3 to 11-33 psu and lowered from 11-33 to 0 psu until the juveniles fell off from the host ( 186-236 h ) , several glochidia of C. plicata and C. tenuis on the host fish survived and metamorphosed. Thus, the results of the present study show that adult mussels cannot survive in brackish water above salinity levels of 6-8 psu; however, glochidia on a host can survive at high salinities. We also considered the possibility of migration of mussels to other geographical areas via brackish water or the sea.