Morphological changes of hemocytes in hemolymph smear preparations of diseased Japanese pearl oyster Pinctada fucata martensii with mass mortality

Abstract

In diseased Japanese pearl oyster Pinctada fucata martensii collected from Ehime, Japan from April to July 1998 where mass mortalities of cultured pearl oyster had occurred since 1996, histopathological features such as atrophy of the connective tissue in the mantle and adductor muscle were commonly observed. These histopathological changes were also reproduced in experimental pearl oyster by inoculation with hemolymph of diseased pearl oyster. Morphological changes of hemocytes in naturally and experimentally infected Japanese pearl oyster were examined. In naturally infected oyster, enlarged cells and the presence of granules and vacuoles in the cytoplasm of hemocytes were observed in hemolymph smear preparations stained with May Grunwald-Giemsa, and these changes were consistent with the histopathological changes. In experimentally infected oyster, these morphological changes of hemocytes were also correlated with the progression of histopathological changes. These results suggest that the observation of morphological changes of hemocytes in hemolymph smear preparations can be a rapid and convenient method for presumptive diagnosis of the disease occurring in Japanese pearl oyster.