PERKINSUS-MARINUS INFECTION AND POTENTIAL DEFENSE-RELATED ACTIVITIES IN EASTERN OYSTERS, CRASSOSTREA-VIRGINICA - SALINITY EFFECTS

Infection by Perkinsus marinus and potential defenserelated activities were determined in eastern oysters (Crassostrea virginica) maintained under different salinity treatments. Oysters were inoculated with trophozoites (106 trophozoites per oyster) of P. marinus and incubated in a closed system for 5 weeks in water of 3, 10, and 20 Opt at 22.0 ± 1.0·C. Oysters were then sacrificed and assessed for P. marinus infection. Simultaneously, potential defenserelated activities of individual oysters from each treatment group including controls were examined. Prevalence and intensity of P. marinus infections were found to be positively correlated with salinity. Infections were detected in all salinity groups, but heavy infections were found only at 10 and 20 ppt. No significant difference in total hemocyte counts and percentage granulocytes existed between control and P. marinus-challenged or between infected and uninfected oysters at any salinity. Total hemocyte counts in oysters maintained at 10 ppt were significantly higher than at 3 ppt but were not significantly different from oysters at 20 ppt. Total hemocyte counts were positively correlated with percentage of granulocytes in oysters. Lysozyme concentrations were significantly lower in the oysters maintained in 10 and 20 ppt water than in those maintained in 3 ppt water. Lysozyme concentration was positively correlated with protein concentration and condition index. Hemolymph protein and condition index appeared to be lower in infected than in uninfected oysters, however, these differences were statistically insignificant. © 1993 Academic Press, Inc.