A Histopathological Study on Serious Cases with Viral Ascites of Yellowtail Fingerling Occurred in Mie Prefecture

Abstract

Viral ascites occurred among fry of yellowtail, Seriola quinqueradiata (3-15 cm in body length) reared in some bays of Mie Prefecture in 1984 and 1985. The serious cases of diseased fish were histopathologically observed in this study. They showed the expanded abdomen and lay on the botoms of net cages, resulting in big mortalities. Internal signs were characterized by accumulation of red or yellow-colored ascitic fluid and catarrhal intestine. Hemorrhage occurred in the liver, stomach and pyloric regions. Pale-coloration was also found in the kideney, spleen and gills. Livers of all fish displayed focal and diffuse necrosis of hepatic cells, followed by congestion and hemorrhage. Pancreatic cells of all cases were necrotized, accompanying with no sign of inclusion bodies. Intestines usually showed desquamative catarrh without invasions of bacteria. Kidneys of most cases showed degeneration and necrosis of renal epithelia and slight necrosis of the hematopoietic tissue. Spleens also showed necrosis of pulps and sheathed arteries. Stomachs of most cases displayed hemorrhage and edema in the submucosa.