The main purpose of this study was to establish the pattern of variability of some hemato-immunological parameters in the mangrove oyster, Crassostrea rhizophorae, from 3 different environmental conditions in Santa Catarina Island: two natural habitats (mangrove and rocks of the coastal bay) and one oyster culture station. The water quality was adequate in all localities. The animals were collected seasonally over a period of one year (n = 30, per locality). The oyster hemolymph comprised two basic cell populations, hyaline (HH) and granular hemocytes (GH). Both cell populations contained carbohydrates and glycogen in their cytoplasm (periodic acid Schiff reaction, PAS staining) and the occurrence of lysosomes was suggested by the detection of acid phosphatase (Gomori's method). Both hemocyte populations were able of phagocytosis of zymosan particles in vitro and producing cytotoxic molecules, such as the superoxide anions (nitroblue-tetrazolium, NBT reduction). The oyster hemograms significantly differed in the different habitats and also among seasons. The total circulating hemocyte counts (THC) and the percentage of GH in the mangrove and rock oysters always differed from each other, but not from those of the cultured oysters. The highest THC and the lowest percentage of GH were always found in summer. The total plasma protein concentration (PC) exhibited a similar seasonal pattern in all oyster populations, with a marked decrease in spring. The PC of the cultured oysters was almost always significantly lower than that of the other oyster populations. The plasma agglutinating titer was higher in the cultured oysters regardless of season. The histological organization of the oyster digestive gland and gills was basically similar to that of other oyster species. Their structural aspect did not show any detectable alteration, corroborating that the oysters were in good health. The results of this study will serve as a basis for further analyses on the monitoring of C. rhizophorae health status and environmental quality in different aquatic habitats.

Mussel (Mytilus galloprovincialis) plasma contains cytotoxic activity against both vertebrate (erythrocytes and mouse tumour) and protozoan cells. Procaryotes (Escherichia coli and Vibrio alginolyticus) were not sensitive to the cytotoxicity. The activity was still present in dialyzed samples but was inhibited by heating at 45 °C. Large individual variability which was not correlated with protein concentration and an increasing number of reactive specimens following injection, suggested that naive mussels were in various stages of immune response. Purification by anion exchange chromatography followed by gel filtration revealed a 320 kDa cytotoxic polymeric protein that acts through a polymerization process after binding onto target cell membranes as revealed by ultrastructural observation.

European and Pacific oysters (Ostrea edulis and Crassostrea gigas) expressed antibacterial activity against both Gram negative and Gram positive bacteria which was most probably due to small proteins. When tested against the marine pathogenic Vibrio alginolyticus, hemocyte lysates of both species were more active than cell-free plasma. Antibacterial activity showed significant individual variability that was dramatically reduced by stimulation through mechanical stress or injection. The number of spontaneously active Pacific oysters increased from 50 to 100% following a single injection of bacteria.

These results strongly support the view that bivalve molluscs possess sensitive immuno-defense mechanisms that will greatly aid the development of aquaculture systems by employing refined techniques of transgenesis.