Groups of Indian edible oysters (Crassostrea madrasensis) of average size 6.6 ± 1.5 cm x 4.2±0.2 cm, were maintained at different salinities of 6, 12,25 and 35 ppt for a period of 1 month. On termination of the experiment, hemolymph samples were withdrawn from adductor muscle sinuses and analyzed for total hemocyte counts, differential hemocyte counts and phagocytic function of the hemocytes. The results revealed that the total hemocyte counts were significantly high at 35 ppt and it was mainly contributed by semigranulocytes. In animals maintained at all other salinity levels, hemocyte counts did not show significant variations. The phagocytic index was significantly low (p < 0.05) in oysters maintained at 6 and 35 ppt salinities compared to other treatment groups.

Crassostrea madrasensis, salinity, hemocyte count, phagocytosis