Chinook Salmon Oncorhynchus tshawytscha is a keystone fish species in the Pacific Northwest. In 2019, unusual mortalities occurred in two different populations of cultured fingerlings from the same facility in California, USA. The systems consist of outdoor, enclosed, flow-through freshwater tanks that are maintained at 18 ± 1°C. Clinical signs and gross findings were only observed in one population and included abnormal swimming, inappetence, lethargy, skin discoloration, and the presence of multifocal nodular and ulcerative skin lesions. Microscopic lesions were infrequent and consisted of severe, locally extensive granulomatous dermatitis and myositis and mild, multifocal, granulomatous branchitis, myocarditis, and hepatitis. Intracellular acid-fast organisms were observed within areas of granulomatous myositis. Posterior kidney swabs were collected and inoculated in nutrient-rich and selective agar media and incubated at 25°C for 2 weeks. Visibly pure bacterial colonies were observed 7–10 d postinoculation. Partial sequences of 16S rRNA initially identified the recovered bacteria as members of the genus Mycobacterium. However, marked variability was observed among Mycobacterium spp. isolates by using repetitive extragenic palindromic polymerase chain reaction fingerprinting. Amplification and sequencing of the ribosomal RNA internal transcribed spacer, 65-kDa heat shock protein, and RNA polymerase β-subunit gene of the cultured isolates identified M. salmoniphilum and M. chelonae, discrete members of the M. chelonae-abscessus complex, isolated from diseased Chinook Salmon fingerlings.

中文翻译：

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奇努克鲑鱼圈养种群中的分枝杆菌和 M. chelonae

奇努克鲑鱼Oncorhynchus tshawytscha是太平洋西北部的重要鱼类。2019 年，来自美国加利福尼亚州同一设施的两个不同养殖鱼种种群发生了异常死亡。该系统由室外、封闭的、流通式淡水水箱组成，水温保持在 18 ± 1°C。仅在一个人群中观察到临床体征和大体结果，包括异常游泳、食欲不振、嗜睡、皮肤变色以及多灶性结节性和溃疡性皮肤病变的存在。显微镜下病变不常见，包括严重的、局部广泛的肉芽肿性皮炎和肌炎，以及轻度、多灶性、肉芽肿性分支炎、心肌炎和肝炎。在肉芽肿性肌炎区域内观察到细胞内抗酸微生物。收集后肾拭子并接种在营养丰富的选择性琼脂培养基中，并在 25°C 下培养 2 周。接种后 7-10 天观察到明显的纯细菌菌落。16S rRNA 的部分序列最初将回收的细菌鉴定为该属的成员分枝杆菌。然而，在分枝杆菌属中观察到显着的变异性。通过使用重复的基因外回文聚合酶链反应指纹图谱分离。核糖体 RNA 内部转录间隔区、65-kDa 热休克蛋白和 RNA 聚合酶 β 亚基基因的扩增和测序鉴定出M.salmoniphilum和M.chelonae，M.chelonae-abscessus复合体的离散成员，分离来自患病的奇努克鲑鱼鱼种。