POSSIBLE CYTOTOXIC EFFECTS OF THE DINOFLAGELLATE, GYRODINIUM-AUREOLUM, ON JUVENILE BIVALVE MOLLUSKS

Juveniles of eight commercially important species of bivalve molluscs (Spisula solidissima, Argopecten irradians, Crassostrea virginica, Myt ilus edulis, Mya arenaria, Ostrea edulis, Mercenaria mercenaria, Placo pecten magellanicus) were exposed in the laboratory to the commonly oc curring dinoflagellate, Gyrodinium aureolum. Histological analyses of gut tissues indicated that the impact of G. aureolum on the shellfish was species-specific. High rates of mortality were noted in the bay sc allop, A. irradians, but not in other molluscan species. There were no pathological differences between control animals and animals fed G. a ureolum in S. solidissima, M. arenaria, or M. mercenaria. The most sev erely affected molluscs were C. virginica and A. irradians. C. virgini ca did not exhibit differences in digestive gland parameters between c ontrol and experimental animals; however, several animals did show sig nificant mantle and gill lesions. Bay scallops exhibited decreased hei ght of absorptive cells and increased lumen diameter after exposure to Gyrodinium suggesting, at least, poor food quality of Gyrodinium. Evi dence of toxic effects was not identified in the digestive gland. Seve ral bay scallops also showed variable amounts of inflammation in the k idney associated with protozoal infestations and variable amounts of p redominately rod-shaped bacteria within the urinary space. Aquaculturi sts, especially of scallop species, should monitor for the presence of G. aureolum. Given its large size (25-30 mu m), G. aureolum could be filtered from incoming water to hatcheries, thus avoiding mass mortali ties of spat and juvenile scallops.