High salinity tolerance during the parasitic period for glochidia of the Freshwater unionid mussel Beringiana beringiana from Hokkaido in experimental tanks

Abstract

Glochidium larvae of the freshwater unionid mussel, which parasitize the fish, can be widely dispersed as the fish migrate. Under captive conditions, the glochidium larvae obtained from Beringiana beringiana were allowed to infect the euryhaline Japanese rice fish (Oryzias latipes) and the salinity tolerance of the larvae was investigated. The fishes were kept in three saline environments (static freshwater environment at 0 psu, fluctuating environment from 0 to 22 psu, and fluctuating environment from 0 to 33 psu), and the number of glochidia and metamorphosed juveniles detached from the host fishes was counted for 15 days. Live juveniles detached from O. latipes were observed in all saline environments, indicating that glochidia of B. beringiana can survive on the host at high salinities, supporting the connectivity among geographically distant mussel populations at the larval stage with diadromous fish species via brackish water or the sea.