Isolation of the pathogen Vibrio tapetis and defense parameters in brown ring diseased Manila clams Ruditapes philippinarum cultivated in England

The Manila clam Ruditapes philippinarum was introduced for aquacultural pur poses to Europe in the 1970s. In 1987, brown ring disease (BRD), caused by Vibrio tapetis, appeared in clams cultivated in Brouenou (Finistere, France ) and later became increasingly widespread and was reported in cultivated a nd wild clams existing on the Atlantic coasts of France and Spain. The pres ent study reports, for the first time, the presence of BRD in clams cultiva ted in England. The etiologic bacterium was isolated and identified using b acteriological and serological techniques. The defence response of affected clams was also studied and significant changes in the hematological and bi ochemical characteristics of hemolymph and extrapallial fluids were demonst rated. Significant mobilization of hemocytes toward the extrapallial fluids , in contact with the main site of infection (mantle-periostracal lamina ar ea), was observed, suggesting a role for these pseudo-internal compartments in the preservation of clam health.