Histopathological Changes Probably Associated with a Virus in Larval and Juvenile Marbled Sole Pleuronectes yokohamae

Abstract

The seed production of marbled sole Pleuronectes yokohamae has been attempted at a hatchery in Kagawa Prefecture, Japan since 1989, while a subacute disease with a considerable amount of mortality occurred in larval and juvenile fish (24-69 days old) in 1989, 1990, 1991, 1997 and 2001. Diseased fish displayed edema, an abdominal distension due to ascites, and exophthalmia. The outbreak of the disease usually continued for 1 month or longer and the cumulative mortality was often over 40%. The evident histopathological features were the formation of multinuclear syncytia and following necrosis in the liver, renal tubules, pancreas and intestinal epithelium, and hemorrhage in the brain, choriocapillaries, stomach and skin. Electron microscopy of affected hepatocytes revealed formation of inclusion bodies consisting of crystalline arrays of virus particles (75-80 nm in diameter). These results suggest that the pathognomonic sign of the present disease is necrosis accompamied by the syncytial formation which would be associated with a virus infection.