Histopathology conditions of cultured oyster, Crassostrea iredalei from southern and east Malaysia

This is a histopathologic survey of cultured oysters, Crassostrea iredalei in Southern Malaysian state and East Malaysia, where incidents of mass mortalities of oysters occurred in 2012. A total of 48 samples of C. iredalei were sampled from both locations. The samples were examined for macroscopic symptoms and were processed for histological study. The collected oysters had similar average shell length between Johor (8.73±0.46 cm) and Sabah (8.75±0.66 cm), respectively. The histopathology examination revealed hypertrophy, hyperplasia, necrosis, thinning of structure such as digestive diverticula, presence of granulocytomas and granulation tissue. "Lesion", "Accumulation of brown cells" and "Hemocyte accumulation" were more severe in Sabah samples compared to Johor samples, except for "Oocysts of Nematopsis sp.". The only pathogen found in this study was Nematopsis sp. and higher prevalence of Nematopsis sp. was found in Johor samples. This study for the first time, documented the histopathology of the sub-population of cultured oysters from two main culture areas in Malaysia, despite the low number of samples.