Rameshkumar P, Nazar A K A, Pradeep M A, Kalidas C, Jayakumar R, Tamilmani G, Sakthivel M, Samal A K, Sirajudeen S, Venkatesan V, Nazeera B M
Mandapam Regional Centre, Central Marine Fisheries Research Institute, Mandapam Camp, Tamil Nadu, India.
Lett Appl Microbiol. 2017 Nov;65(5):423-430. doi: 10.1111/lam.12800.
Mass mortalities of cobia, Rachycentron canadum, sub-adults occurred during August 2013 in cage culture in the Gulf of Mannar, Mandapam Tamil Nadu, India. The epizootic of disease was started with typical classical clinical signs followed by acute mortality. Grossly, severe haemorrhage and congestion were observed in the gastric mucosa. The abdomen was distended with peritoneal fluid. The heart revealed haemopericardium and fibrinous pericardium. Histologically, the gastric mucosa showed severe erosion and necrosis. Haemorrhagic pericarditis and an increased size of the melano macrophage centre (MMC) in the tail kidney were other histopathological changes. Vibrio sp. was isolated from the gastric lesions and heart blood swab of moribund fishes and it was found to be virulent to the cobia fingerlings. After the challenge, the same bacterium could be re-isolated from moribund fingerlings. The 16S ribosomal RNA of the isolate was amplified and blast analysis of the sequence confirmed that the pathogen was Vibrio alginolyticus. The confirmation was also correlated with its cultural, biochemical and pathomorphological changes. This is the second report and the first incidence of epizootics with severe pathological lesions in cultured cobia in India. The study throws light on the pathology of vibriosis. By practising cage farm management measures, occurrences of infection may be prevented.
The epizootics of vibriosis caused serious economic losses to farmers. Natural blooms of the pathogen can be prevented by sea cage management measures such as, changing the inner net of the cages, changing the location of the cages to relatively clean water (about 50 m apart) from the affected site and providing shade over the cages while the water temperature rises. Supplementation of the feed with immunostimulants and mineral mixture may be practised to improve the immune response against infection. Early diagnosis and sea cage management measures may prevent occurrences of the infection.
2013年8月，印度泰米尔纳德邦曼达帕姆马纳尔湾的网箱养殖中，军曹鱼（Rachycentron canadum）亚成鱼出现大规模死亡。疾病流行始于典型的经典临床症状，随后出现急性死亡。大体上，胃黏膜观察到严重出血和充血。腹部因腹腔积液而膨胀。心脏显示心包积血和纤维素性心包炎。组织学上，胃黏膜显示严重糜烂和坏死。出血性心包炎以及尾肾中黑素巨噬细胞中心（MMC）增大是其他组织病理学变化。从濒死鱼的胃部病变和心脏血拭子中分离出弧菌属，发现其对军曹鱼幼鱼具有毒性。攻毒后，可从濒死幼鱼中再次分离出相同细菌。对分离株的16S核糖体RNA进行扩增，序列的blast分析证实病原体为溶藻弧菌。该确认也与其培养、生化和病理形态学变化相关。这是印度养殖军曹鱼中出现严重病理病变的第二次报告及首次疫情。该研究揭示了弧菌病的病理学。通过实施网箱养殖管理措施，可预防感染的发生。
弧菌病的疫情给养殖户造成了严重的经济损失。可通过网箱管理措施预防病原体的自然爆发，如更换网箱内网、将网箱位置从受影响地点转移到相对清洁的水域（相距约50米）以及在水温升高时为网箱提供遮荫。可在饲料中添加免疫刺激剂和矿物质混合物，以提高对感染的免疫反应。早期诊断和网箱管理措施可预防感染的发生。
