Document Type



Virginia Institute of Marine Science

Publication Date



Journal of Shellfish Research





First Page


Last Page



A selective breeding program was implemented to attempt to decrease the disease susceptibility of the eastern oyster, Crassostrea virginica, to Perkinsus marinus. Six oyster strains were spawned and the progeny exposed to Haplosporidium nelsoni (MSX) and P. marinus in the lower Chesapeake Bay. Three strains, a Delaware Bay MSX-resistant strain, a Delaware Bay native strain, and a Mobjack Bay native strain (lower Chesapeake Bay) were exposed for three years (1988-90); three other strains, a separate Delaware Bay MSX-resistant strain, a lower James River native strain (lower Chesapeake Bay) and a susceptible control strain, were exposed for two years (1989-90). During the study period, P. marinus abundance was high and increased each year; H. nelson/ abundance was low and decreased each year. Both strains of MSX-resistant oysters developed by Rutgers University were highly susceptible to P. marinus. Cumulative mortality at the end of the study was 99% for both strains and growth virtually stopped after acquisition of P. marinus. Mean shell height did not reach market size in either MSX-resistant strain. All native strains (Delaware Bay, Mobjack Bay and James River) had about 80% cumulative mortality, mainly from P. marinus, but the Mobjack Bay strain also experienced moderate mortality from H. nelson/. However, these strains continued growing and survivors reached market size during the study period. The MSX-resistant strains offer little immediate benefit in a selective breeding program for the Chesapeake Bay oyster industry because of their high susceptibility to P. marinus and poor growth; however, they may be valuable, especially in crosses with native strains, during periods of H. nelson/ resurgence and P. marinus decline. The three native strains performed better than the resistant strains and will be utilized, both as direct lines and as intraspecific hybrids, in a continuing selective breeding program to decrease the disease susceptibility of C. virgin/ca stocks.


oysters, disease, Chesapeake Bay, Haplosporidium, growth, mortality