Experimental infections of a disease causing mass mortalities of Japanese pearl oyster Pinctada fucata martensii by tissue transplantation and cohabitation

Mass mortalities accompanied by the changing of the color of the adductor m uscle to red-brown have been occurring in the cultured Japanese pearl oyste rs Pinctada fucata martensii in western Japan. Histopathological changes co mmonly appeared in the loose connective tissue of the mantle and less frequ ently in the adductor muscle in the affected pearl oysters of the farms. To clarify the possibility of the involvement of an infectious agent in this epizootic, two infection experiments were performed by transplantation of t he mantle piece of the affected pearl oysters into healthy oysters and coha bitation of the affected and healthy pearl oysters. During the experimental period of three months, the mortality of the test group was 13.3% in the t ransplantation and 30.8% in the cohabitation. The color of the adductor mus cle of all survivals had changed to red-brown and the pathological changes were also reproduced in both experiments. On the other hand, mortality and color changes in the adductor muscle were not observed in the corresponding control groups. Accordingly, these results strongly suggest that the mass mortality of the cultured pearl oysters is caused by an infectious agent.