In recent years,a kind of disease broke out in Siberian sturgeon breeding base of Beijing.The main symptoms of diseased Siberian sturgeon were that the heart surface was observed to have a large number of rice grain-like,purple-brown cystic neoplasm.The whole heart looks like mulberries shape.The mortality rate were as high as 60% or more.Sick fish were about one year old.Water temperature was around 27℃ or so.In order to diagnose and preliminarily discuss the cause on heart surface cystic neoplasm of Siberian sturgeon,the histopathologic changes of the diseased Siberian sturgeon and the morphology of the pathogen were observed under optic and electronic microscopes.The results show that the heart surface of sick Siberian sturgeon can be observed in a large of rice grain-like,purple-brown cystic neoplasm.The heart was like mulberries shape.The epicardial mesothelial cells and connective tissue were between obvious hyperplasia.Neoplasm was formed.Epicardial lesions were dynamic process.Epicardial lesions were becoming more severe from mild.The main show were epithelium by flat to cuboidal epithelium.The cyst walls were gradually thickening and differentiating,so that the increasing cysts lined become more.The cyst cavity had a number of undifferentiated spherical,spindle and so on the different mature degrees of blood cells and vascular tissue,and infiltration with a lot of free or round state distribution inflammatory cells.The whole lesions looked like a kind of tumor type of malignant hyperplasia,myocardial cells were swelling,fractured,dissolved and necrotic.The liver lesions were hepatic steatosis and infiltration of inflammatory cells.Renal interstitium and spleen lymphocytes increased.Gill lamellae were observed between the large number of bacterial invading epithelial cells;the epithelial cells of gill lamellae were severe swelling and hyperplasia.Under transmission electronic microscope,a large number of bacteria were observed in the heart,liver,spleen and kidney.The microscopic and ultrastructure changes speculate that its etiology may be associated with trace elements and the bacteria are not the direct cause of the disease.To provide basic information for the prevention and treatment,clinical diagnosis and pathogenesis and related research,the hispathological changes were more systematically researched on Siberian sturgeon mulberry heart disease.