Aetiology And Pathomorphology Of Bacterial Septicemi In Channel Catfish And Immunization Of Inactivated Vaccine

A communicable diseases of Channel catfish was outbreaking in Mianyang,Meishan and Deyang during 2007.The main gross pathologic changes of diseased fish showed hyPeraemia, hemorrhage and a lot of irregular, variably sized areas of depigmentation on the body surface,distension of abdomen,swelling. liver, kidney and spleen,ascite,bleed gastroenteritis,intussusception in rectum. This diseaes was highly morbility and mortality. It has caused large economical loss which destabilized the confidence of culturist. Nevertheless, the pathogenetic condition was difficult to control. Beacause the pathogeny was unknown, and drug abuse. Therefore,etiological study was conducted in order to solve the disease problems and maintain the sustainable development for the industry.Isolated a bacteria named D070801 from the sick Channel catfish. It was Gram negative, rod bacteria.The bacteria can't utilize most of sugars without glucose,amylomaltose, Carubinose, Cane-sugar, Diabetin, Esculin.The bacteria are Oxidas-positive, Orinithine-decarboxylase-positive, Lysine decarboxylase-Positive, Amylase-positive, DNAase-positive, Arginine hydratase-Positive, LiPase-Positive, Methyl-red-positive. Indole-positive,VP-positive.Traditinal biochemical and 16S rDNA sequence of strain show that D070801 was A.veronii. In the phylogenetic tree D070801 and A.veronii were the closest relative with 99.1% sequence similarity.In a word,the pathogenic bacteria of Channel catfish. diseases was A.caviae. The pathogenic bacteria was hypersensitive to Deoxycycline, Florfenicol, Stmycin, Fradiomycin, Amikacin and Norfloxacin.The Macropathology of artificial challenge by Aeromonas veronii was studied. Gross changes examination of the infected fish showed that, depigmentation on the body surface, distension of abdomen, flooded fluid in the peritoneal cavity,the liver,kidney,spleen encephalo,fat,mesentery were engorgement,and there maybe bloody mucus and fluid in lumen, intussusception in rectum.The Histopathology of channel catfish infected with Aeromonas veronii was studied by light microscope examination. In the histopathology, the muscle, gastrointestinal tract, gill, and the fundamental organs were damaged. They were degeneration, necrosis, inflammatory cell infiltration.especially,serious lesions occurred in the kidney,liver,gastrointestinal tract and spleen. The kidney showede edema degeneration and necrosis in renal tubular epithelia, and necrosis with marophages and neutrophi in the hematopoietic tissue.The liver showed edema,vacuolar degeneration and necrosis.The spleen showed congestion,hemorrhage,diminution of lymphoid tissue and infiltration.The bowel showed enteremia,necrose and desquamation in enteric epithelia,and the submucosa of hydrops. The menigeal showed hyperemia and angiectasis.The detected result of immunization experiment of bath immersion showed that the content of lysozyme, protein content and antibody titer from immunity class were all significant increased in 7d,21d,35d after the first immunization. And the experiment of RPS showed that the relative percent survival rates of the first immersion is 32.6%,The boost immersion is 48.8%.