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

The relationship of potential defense-related cellular and humoral act ivities and the susceptibility of eastern oysters Crassostrea virginic a to the parasite Perkinsus marinus were examined at 10, 15, 20 and 25 -degrees-C. Oysters were acclimated at experimental temperatures for 2 0 d and then challenged with P. marinus. Total hemocyte counts (TC) an d percentage of granulocytes (PG) 20 d after temperature acclimation w ere higher in oysters dt high than at low acclimation temperature. Hig her 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 pr evalence 46 d after challenge by P marinus was 100, 91, 46 and 23% res pectively, for oysters at 25, 20, 15 and 10-degrees-C. Disease intensi ty increased with temperature. OysterS dt higher temperatures had grea ter PG and TC and hemocyte phagocytic activity. No difference was foun d in TC and PG between control and challenged oysters within each temp erature treatment. Bleeding may to some extent reduce TC and PG in oys ters. P did not vary much among temperatures. No reduction of P in oys ters was found due to P. marinus challenge and infection. L tended to be higher in oysters at lower than at higher treatment temperatures. T he oysters at 10-degrees-C had the highest L concentration and lowest P. marinus infection. But, it is not known whether the high extracellu lar L in oysters at 10-degrees-C is attributable to the low P marinus susceptibility in these oysters. There was no significant difference i n condition index (CI) between control and challenged oysters and betw een infected and uninfected oysters. However, CI decreased with increa sing 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. marinu s infections.