Abstract
Mass mortalities caused by akoya oyster disease have been occurring in cultured Japanese pearl oyster Pinctada fucata martensii in western Japan. Although the involvement of some causative agents was suggested, the cause of the disease is still unidentified. In this study, an experimental infection was performed by cohabitation of the diseased and healthy pearl oysters. A high mortality and characteristic disease conditions were observed in the test group. This result reconfirmed that this disease is caused by a certain infectious agent. To clarify the tissue distribution of the causative agent in diseased pearl oysters, two experimental infections were performed by transplantation of pieces of various tissues or injection of homogenates of various tissues from diseased pearl oysters into healthy pearl oysters. The hemolymph, mantle and adductor muscle showed high infectious titers compared with those of the heart, digestive gland and hemocytes. The mantle had the highest infectious titer. Moreover, injection of the supernatant of a mantle homogenate also transmitted the disease to test pearl oysters. These results suggest that the causative agent is concentrated in the mantle.
