PERKINSUS-MARINUS SUSCEPTIBILITY AND DEFENSE-RELATED ACTIVITIES IN EASTERN OYSTERS CRASSOSTREA-VIRGINICA - TEMPERATURE EFFECTS

The relationship of potential defense-related cellular and humoral activities and the susceptibility of eastern oysters Crassostrea virginica to the parasite Perkinsus marinus were examined at 10, 15, 20 and 25-degrees-C. Oysters were acclimated at experimental temperatures for 20 d and then challenged with P. marinus. Total hemocyte counts (TC) and percentage of granulocytes (PG) 20 d after temperature acclimation were higher in oysters dt high than at low acclimation temperature. Higher protein (P) and lysozyme (L) concentrations were found in oysters at 10 and 15-degrees-C. No significant differences in hemagglutination (H) titers due to temperature acclimation were observed. Infection prevalence 46 d after challenge by P marinus was 100, 91, 46 and 23% respectively, for oysters at 25, 20, 15 and 10-degrees-C. Disease intensity increased with temperature. OysterS dt higher temperatures had greater PG and TC and hemocyte phagocytic activity. No difference was found in TC and PG between control and challenged oysters within each temperature treatment. Bleeding may to some extent reduce TC and PG in oysters. P did not vary much among temperatures. No reduction of P in oysters was found due to P. marinus challenge and infection. L tended to be higher in oysters at lower than at higher treatment temperatures. The oysters at 10-degrees-C had the highest L concentration and lowest P. marinus infection. But, it is not known whether the high extracellular L in oysters at 10-degrees-C is attributable to the low P marinus susceptibility in these oysters. There was no significant difference in condition index (CI) between control and challenged oysters and between infected and uninfected oysters. However, CI decreased with increasing temperatures. The H titers were not associated with any measured variables. The greater TC, PG, and phagocytic capability in oysters at higher temperatures did not result in fewer or less intense P. marinus infections.