Variations in the morphology and hemocytic responses of Asian green-lipped mussel, Perna viridis l., in selected aquaculture sites in Manila Bay

Abstract

Many studies about on ecology and hydrodynamics in the Indo-Pacific have utilized Perna viridis hemato-immunological responses as bioindicators of pollution and environmental stressors due to its filter-feeding capacities. This study determined the morphology and hemocytic responses of populations of P. viridis (n=30) obtained from aquaculture sites in Bacoor (Cavite), Hagonoy (Bulacan), and Navotas (Metro Manila) coastal areas of Manila Bay. Morphology of bivalves was characterized by measuring shell length and meat weight ratio while hemolymph from the adductor muscle and the homogenized of shellfish meat were used in the test for hemocytic responses and presence of gonyaucoloid toxins, respectively. Results showed that average shell length varied significantly among the three populations; with the Bacoor group having the highest mean in shell length while Navotas group has the lowest. Whereas the mean meat weight ratios did not vary between the Hagonoy and Bacoor populations. The Navotas group has the highest average meat weight values while Hagonoy has the lowest. The total hemocyte counts were observed to be significant only between Navotas and Bacoor populations. Two hemocyte populations were determined by flow cytometric analysis and showed that granular hemocytes comprised no more than 25% of the total circulating hemocytes of the three areas while hyaline hemocytes comprised 76-96%, with highest values of the phagocytic granular hemocytes found samples from Bacoor and the least in the Navotas population, showing the same trend as shell length and opposite trend as meat weight ratio. While there are variations in morphology and hemocyte responses in the P. viridis populations, the samples tested negative for gonyaucoloid toxins (Saxitoxin, decarbamoylSaxitoxin, neoSaxitoxin, and gonyautoxin1and4) for all three locations. According to previous studies, variations in the morphology and hemocyte responses could be attributed to differences in temporal establishment of bivalve populations, the periodic hypoxia observed in the bay, and pollution of heavy metals and other contaminants in aquaculture sites of the coastal bay areas studied.