Occurrence of hematopoietic neoplasms in Virginia oysters (Crassostrea virginica)

A neoplastic disease of the hematopoietic system of oysters was found in tray-cultured native and laboratory-bred populations and was associated with mortalities during field monitoring. The disease, characterized by nuclear abnormalities and intensive proliferation of hemocytes, was first observed at the Virginia Institute of Marine Science in 1963. Cases rarely occurred during 14 years (1959-1973 inclusive) of regular sampling and monitoring of thousands of oysters. However, two groups exhibited a high susceptibility to this disease in a program of intensive inbreeding to achieve genetic resistance to oyster pathogens.