Diseases of maricultured gastropods and bivalves in Japan

Abstract

Recently, some serious disease problems have occurred in cultured species of gastropods and bivalves in Japan. Among the current problems, amyotrophia of abalones (Nordotis species) and epizootic mortality of pearl oysters (Pinctada fucata martensii), are briefly described in this minireview. Amyotrophia occurs in juveniles of Japanese black abalone (Nordotis discus discus) and two other species of abalones (N. discus hannai, N. madaka) in hatcheries in the late spring, causing muscle atrophy in the mantle and epipodium and abnormal cell masses in the nerve tissues and gills. Although the disease was produced in susceptible juveniles of black abalone by inoculating filtered homogenate of affected abalones, the causative agent has not yet been determined. Epizootic mortalities of pearl oyster have been observed in western Japan since 1996. The adductor muscle of diseased animals often becames reddish and various histopathological changes, such as necrosis and atrophy, occur in both the adductor muscle and heart. Association of the toxic dinoflagellate Heterocapsa circularisquama, the protistan parasite Perkinsus sp. and birnavirus were first suspected, but now a virus or a filterable agent is thought to be the causative agent of the mortality.