In recent years, infection with Shewanella putrefaciens has emerged as a serious problem in freshwater aquaculture. In the present study, we report large‐scale mortality in farmed tilapia Oreochromis niloticus from Hisar, North India. The diseased tilapia exhibited lethargy, swimming near the water surface, fin rot, hemorrhages on the operculum, and approximately 40% mortality. Gram‐negative, motile, catalase, and oxidase‐positive bacilli were isolated from the kidney of affected tilapia and confirmed as S. putrefaciens on the basis of biochemical tests and 16S rRNA gene sequencing. The antimicrobial sensitivity test revealed that S. putrefaciens strains were sensitive to quinolone, nitrofuran, tetracycline, aminoglycoside, cephalosporin, aminocyclitol, sulphonamide, and macrolide antibiotics, but resistant to beta‐lactam and glycopeptide antibiotics. The histopathological examination revealed degenerative changes in the kidney, liver, spleen, and intestine suggesting systemic infection. In experimental infection studies, the disease was reproduced in naive tilapia, and the clinical signs resembled those observed in natural cases. Further more, S. putrefaciens was re‐isolated from the kidney of challenged tilapia, fulfilling Koch's postulates. Therefore, the mortality in tilapia was attributed to S. putrefaciens infection.

中文翻译：

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在印度因感染希瓦氏菌引起的罗非鱼养殖尼罗罗非鱼的大规模死亡

近年来，腐烂希瓦氏菌的感染已成为淡水水产养殖中的一个严重问题。在本研究中，我们报告了北印度希萨尔养殖的罗非鱼Oreochromis niloticus的大规模死亡。患病的罗非鱼表现出嗜睡，在水面附近游动，鳍腐烂，腹出血和大约40％的死亡率。从受影响罗非鱼的肾脏中分离出革兰氏阴性，活动性，过氧化氢酶和氧化酶阳性细菌，并根据生化测试和16S rRNA基因测序将其确认为腐烂链球菌。抗菌药敏试验表明，腐烂链球菌菌株对喹诺酮，硝基呋喃，四环素，氨基糖苷，头孢菌素，氨基环糖醇，磺酰胺和大环内酯类抗生素敏感，但对β-内酰胺和糖肽抗生素具有抗性。组织病理学检查显示肾脏，肝脏，脾脏和肠道的退行性改变提示系统性感染。在实验性感染研究中，该疾病在幼稚的罗非鱼中繁殖，其临床症状与在自然病例中观察到的相似。此外，腐烂链球菌从受挑战的罗非鱼的肾脏中重新分离出来，符合科赫的假设。因此，罗非鱼的死亡率归因于腐烂链球菌感染。