Virginia Institute of Marine Science
Journal of Insect Pathology
A short, sharp eplzootic disease of oysters on Seaside of Eastern Shore, Virginia, has been associated with a new pathogen, Haplosporidium costale Wood and Andrews. Native oysters in trays have shown closely timed May-June losses for three consecutive years. Losses at other seasons were small. May-June losses ranged from 12 to 14 percent in 1959 to 36 to 44 percent in 1960. James River oysters moved to Seaside showed higher losses than natives after a year of acclimation. Oysters in Bayside creeks revealed late summer losses caused by Dermocystidimn marinmn Mackin, Owens, and Collier rather than May-June deaths.
The new pathogen was found in live oysters from March to July, and in a high proportion of gapers in May and June. The epizootiology is well established for these periods but unknown for the rest of the year. Increasing prevalence of another pathogen ("MSX"), causing "Delaware Bay disease," has complicated mortality studies.
Losses are most serious in older oysters which have been held beyond the usual period of culture. Careful timing of planting and early harvesting permit oystermen to a void serious losses.
Andrews, Jay D.; Wood, John L.; and Hoese, H. Dickson, Oyster Mortality Studies in Virginia: Ill. Epizootiology of a Disease Caused by Haplosporidium costale Wood and Andrews (1962). Journal of Insect Pathology, 4, 327-343.