Further evidence of regular sporulation by Haplosporidium nelsoni in small oysters, Crassostrea virginica.

During a field study to determine the susceptibility of the Pacific oyster Crassostrea gigas to Chesapeake Bay oyster pathogens, sporulation of Haplosporidium nelsoni was observed in eastern oysters Crassostrea virginica being used as controls. The C. virginica were obtained from 2 sources on 19 May 1993, a wild population in the upper Rappahannock River, Virginia (59.6 mm mean shell height) and a hatchery-reared population from Chesapeake Mari-culture that was held in the Wye River, Maryland (42.2 mm mean shell height); they were deployed in the York River, lower Chesapeake Bay on 29 June 1993. Both groups of C. virginica became heavily infected with H. nelsoni in early July 1993. Sporulation was observed in both groups on 8 September but was most prevalent in the smaller Maryland oysters where it reached 36% of infected oysters. Oysters of 72.3 mm mean shell height deployed at the same location in May 1993 also became heavily infected with H. nelsoni, but no cases of sporulation were observed in these larger oysters. These results provide further evidence that sporulation of H. nelsoni occurs regularly only in oysters approximately 1 yr old or less.