Pathological Observation Of American Eel Infected By Bacterial Pathogens From Diseased Eels

Eels are important marine aquaculture species due to its delicious taste and high economic value. Since the 1990 s, bacterial pathogens infected farmed eels and brought serious economic losses. To study the pathogenicity and pathological changes of the infection of four species of bacterial pathogens to farmed American eels, these pathogens were used to infect American eel, organs from dead or dying eels were collected to prepare histopathological slice and staining. At the same time, organs from dead or dying eels infected with Aeromonas jandaei or Edwardsiella tarda were collected, and the diseased tissue of organs and pathological changes in the cells were studied by ultramicrotomy techniques and electron microscopy staining technique. These results will lay the foundation for the diagnostic pathology of the four kinds of bacterial diseases and the method of immune control. The results were presented as follows:(1)Ulcers was observed in the injection site of American eels infected by Aeromonas hydrophila, while histopathological changes were mainly observed in kidney, the glomerular capillary was swelled and endothelial cells were proliferation; renal capsule cysts were narrow and renal interstitial was bleeding, with large amounts of inflammatory cell infiltration; kidney tubular showed degeneration or disintegration and the epithelial cells were swell. Diffuse bleeding was observed in the liver. Liver cells were edema round and vacuolar degeneration, and some liver cells dissolved and disappeared; hepatic central vein dilated and filled with erythrocytes; hepatic sinusoid was congestion and liver tissue was hemosiderosis.(2)Ulcers was observed in injection site of American eels infected by Aeromonas jandaei, the organs showed a certain degree of pathological changes. Liver tissues were inflammation and phagocyte cells were infiltration; liver cells were widespread degeneration and some liver cells were necrosis. Heart blood vessels dilated to thrombosis, and some occupied the entire vascular. Spleen interstitial arterial walls were edema and thicken, with fibrous-like substances oozing and lymphocyte infiltration. Kidney glomerular disintegrated, and a large number of lymphocytes were infiltration; kidney tubules disintegrated, leaving only remnants of necrotic tissue.(3)Acute and chronic inflammations were observed in American eels infected by Edwardsiella tarda. In the acute inflammation, multiple necrosis was noticed in the liver, with the accumulation of macrophage and liver cell degeneration and necrosis. In the chronic infections, liver cell necrosis and showed large area of fibrosis; stromals of the cells were widened and full of bile and mononuclear macrophages, and central venous wall in the liver was dilation.(4)The epicardium of American eels infected by Vibrio vulnificus was edema and widened with oval nodules. The spleen was inflammation, and red pulp area was presented a large number of lymphocytes, while red blood cells significantly reduced. Spleen was congestion and hemorrhage, spleen parenchymal cells was necrosis, and stromal between cells were widened. Renal tubular epithelial cell was necrosis and disintegration, with renal unit structure disappeared; renal interstitium was widened and bleeding, and large number of red blood cells were degeneration and necrosis. Liver cells were edema, and bile duct was blockage and filled with bile; many liver cells were severe swelling and vacuolar degeneration, and some liver cells were necrosis.(5)The ultra-structural pathological changse were studied in American eels infected by Edwardsiella tarda. The glomerular capillary was dilation, and intravascular stained endothelial cells increased. In addition, the ultrastructural pathological changes were studied in American eels infected by Aeromonas jandaei. The hematopoietic tissues in the kidney tubule showed apparent lesions and blood sinus surrounding matrix disappeared; liver tissue was hemorrhage with a large amounts of nucleus concentrated and stained red blood cells after necrosis; Heart meningitis was observed, and a large number of cellulose membrane-like substances were appeared.