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中文摘要：
2006年6月至7月，浙江萧山的部分乌鳢养殖池塘出现大规模死鱼现象，发病率达35％，死亡率100％。病死鱼鱼龄多在18个月左右，体长30--35cm。症状主要表现为体表、鳍条充血，肝、脾、肾等内脏器官出现直径1—5mm的乳白色结节。从病鱼的肝脏和肾脏中分离到菌株W060622，经光镜、电镜观察，在形态上均表现为长或短的分支状杆菌。回归感染试验证实W060622即为引起此次乌鳢结节病的病原菌。通过16SrRNA基因的全序列测定，并与Genbank中相关序列进行比对，发现W060622与鲕鱼诺卡氏菌NocardiaserioleaJCM3360’（Z36925）的16SrRNA基因序列相似性达99．9％。结合菌株回归感染、形态学和生物学特征及16SrRNA分子鉴定，确定W060622为蛳鱼诺卡氏菌。
英文摘要：
Epizootics of nocardiosis in reared snakehead, Ophiocephalus argus Cantor, occurred in the north part Of Zhejiang Province ,China,in recent years. It is a chronic systematic disease which bring significant loss in aquiculture. And an epizootic disease of snakehead,cultured in brackish ponds was investigated by our workgroup in Xiaoshan,in Zhejiang Province, China, from June to July 2006. The cumulative mortality within 30d was 35 % （ 180000 out of 500000） and the mortality was as high as 100%. The clinical signs, pathogenic morphology,virulence, biochemical characterization, ultrapathology and 16S rRNA gene were observed and analyzed. This is the first study on Nocardia sp. -infected snakehead in aquaculture. We try to make it the reference of prevention and cure on nocardiosis in snakehead and also provide new contents about diseases in snakehead. The diseased fish were 18 months old with individual length from 30 to 35 cm,body weight from 250 to 400 g. Multiple,ivory-white nodules,1--5 mm in diameter, were scattered on several internal organs, especially the liver, spleen and kidney. Gram-positive rods, often seen as branched fragmented filaments, were detected in Gram-stained smears of scrapings of the organ lesions. Bacteria were isolated from the liver and kidney of diseased fish and numbered W060622. Experimentally induced nocardiosis in snakeheads challenged with the bacterium isolated from a natural outbreak produced the same pathological changes as observed in naturally infected fish. In addition,the bacterium was re-isolated in pure culture from challenged animals only. These observations confirm the bacterium as the aetiological agent of this disease in cultured snakeheads. The morphology of isolated bacteria from Tryptic soy agar （TSA） and Ogawa＇s medium （OM） were bead-like or long, slender, filamentous rods both under microscope and electron microscope. Batches of bacteria were found in kidney tissue and cells,whereas, no virus and other prokaryotes were found under electron microscop
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