Susceptibility Of Diploid And Triploid Pacific Oysters, Crassostrea Gigas (Thunberg, 1793) And Eastern Oysters, Crassostrea virginica (Gmelin, 1791), To Perkinsus marinus

The susceptibility of Pacific oysters, Crassostrea gigas, to the oyster parasite Perkinsus marinus was compared with that of eastern oysters, Crassostrea virginica, in two separate experiments. Experiments were conducted in flow-through seawater systems with quarantined effluent. Oysters were challenged by addition of infective P. marinus. In the first experiment, which used only diploid oysters, 40% of C. gigas became infected with P. marinus after 83 days compared to 100% of C. virginica. In the second experiment, which examined susceptibility of diploid and triploid individuals of both species, prevalence was high in all groups after 60 days. In C. virginica, heavy and moderate infection intensities prevailed while C. gigas exhibited only light infections. Cumulative mortality of C. virginica after 150 days was 100% for the diploid group and 97.7% for the triploid group. Cumulative mortality of C. gigas after 150 days was 25 .1 % for the diploid group and 34.3% for the triploid group, but this mortality did not appear to be disease related. Thus, C. gigas was consistently more tolerant of P. marinus than was C. virginica, and triploidy provided no increased disease tolerance for either species.