The toxic effect of the heavy metal cadmium on the oxygen consumption and histology of gill clam Meretrix casta was studied. The clam were exposed for 10, 20 and 30 days in 10% sub lethal concentration of 96 hr LC50 of cadmium (1.25 mg/l). Cadmium significantly decreased the oxygen consumption rate. The oxygen consumption rate decreases exponentially with increase in exposure periods. Appreciable changes were noticed in the gills of clams within 7 days of 10% sub lethal exposure. Sloughing of basal epithelium, damaged epithelial cells and swelling of lamellae with haemocytes were observed. The damage was more severe and progressive after 14 days exposure. Vacuolization of epithelial cells and loss of inter lamellar junctions were prominent in the gills of clams exposed to 21days.
