HAPLOSPORIDIAN INFECTIONS OF THE PACIFIC OYSTER, CRASSOSTREA-GIGAS (THUNBERG), IN CALIFORNIA AND JAPAN

Haplosporidian infections were observed in adult and seed Pacific oyst ers, Crassostrea gigas (Thunberg), in Drakes Estero, CA, and in seed P acific oysters from Matsushima and Watanoha Bays, Japan. Up to 7% of d omestic Pacific oysters and those imported from Japan that were examin ed from Drakes Estero had mild systemic or localized haplosporidian in fections. Plasmodia were observed within the gills and connective tiss ues surrounding the stomach and intestine or, more commonly, within th e epithelium of the heart. An inflammatory response was observed in re sponse to plasmodia within connective tissues; inflammation was not ob served in infections within the heart. Multinucleated plasmodia were a lso observed in the heart of 1-3% of seed oysters examined from Matsus hima and Watanoha Bays, Japan. Results from this study suggest that ha plosporidia are established at very low levels in Pacific oysters rear ed in Drakes Estero, CA. These data also suggest that Pacific oysters imported into Drakes Estero from Matsushima Bay, Japan, were a likely source of the introduction of the haplosporidian in California.