Phagocytic and chemotactic responses of manila and carpet shell clam haemocytes against Vibrio tapetis, the causative agent of brown ring disease

Phagocytic and chemotactic activities of haemocytes from two clam species, Tapes decussatus andT. philippinarum have been studied using bacterial challenge. Three strains of Vibrio tapetis, the causative agent of the brown ring disease affecting these clam species, and one strain of Escherichia coli were used in the study. All extracellular products of the bacterial strains were demonstrated to be chemoattractants to clam haemocytes, however, significant differences (P<0·025) in migration indices of haemocytes were obtained between the E. coli and V. tapetis strains. Phagocytosis by T. decussatus and T. philippinarum haemocytes is apparently a non-specific process, although affected by the viability of the microorganisms. Soluble haemolymph proteins are not required for identification of non-self or in the internalisation process.