Laboratory and field studies on Glugea stephani (Hagenmuller), a microsporidan parasite of pleuronectid flatfishes.

The microsporidan Glugea stephani is a common parasite of juvenile English sole (Parophrys vetulus) in Yaquina Bay, Oregon. Field observations indicated that fish became infected only in the upper estuary where summer temperatures were above 15C and the incidence of infection reached 79.8% in the late fall. Laboratory infections developed and parasite growth occurred only at or above 15C. The parasite was successfully transmitted to juvenile English sole by brine shrimp (Artemia salina) and amphipod (Corophium spinocorne) vectors as well as by direct ingestion of spores by the host. Infections that resulted from ingestion of spore-carrying vectors were much heavier than those resulting from the direct ingestion of spores. The speckled sanddab (Citharichthys stigmaeus), a nonpleuronectid flatfish, and chum salmon (Oncorhynchus keta) were refractory to G. stephani infection in the laboratory.