Examen microscopique des huitres plates de l'estuaire du Belon

Samples of oysters, Ostrea edulis, collected from badly decimated beds in the Belon estuary in July 1969 and July 1970 were examined microscopically in an attempt to determine the cause of death. Although large numbers of ciliates belonging to the ancistrocomidae were found in the digestive mass, no sign of any parasitic or viral disease was found in the tissues. On the other hand, oysters in poor condition exhibited a hypersecretion of mucopoly-saccharides covering the whole surface of the gastric epithelium. This condition, and the existence of a massive infiltration of the connective tissue and the blood sinuses by hyaline haemocytes, indicates a defense reaction against some unknown changes in the physico-chemical environment.