Histopathological Features of Cultured Japanese Amberjack Seriola quinqueradiata with Ascites Occurring in the Winter

A winter outbreak of ascites in cultured Japanese amberjack Seriola quinqueradiata was examined. Affected fish displayed bloody ascitic fluid in the peritoneal cavity, their hearts were covered with a white membrane, their livers were congested and their kidneys were swollen. Renal tubular epithelia displayed extensive necrosis and often contained hyaline droplets, while some glomeruli showed atrophy and necrosis. Hematopoietic tissue in the kidney contained some swollen reticular cells. In the heart, an inflammatory reaction accompanied by edema, hemorrhage and fibrin deposition occurred in the epicardium of the atrium and ventricle and in the pericardial cavity. The epicardium and pericardium were partially adhered to each other. Hepatic lesions included dilatation of sinusoids accompanied by severe edema and congestion. Edema and fibrin deposition were often observed in the hepatic serosa and perivascular tissue. Splenic tissues with atrophied pulp showed definite increases in trabecula thickness. These findings suggest that the examined fish might have a systemic circulatory disturbance due to cardiac lesions associated with renal failure.