Mycobacteriosis caused by Mycobacterium marinum in Pterophyllum scalare: first evidence from China

Abstract In November (Deng 2023), a continuous outbreak of mortality was observed in Pterophyllum scalare at a farm in Liaoyang, Liaoning Province, China. The diseased fish presented white nodules in various tissues. A dominant strain, 2HYL117, was isolated from the nodular lesions of diseased fish. Strain 2HYL117 was identified as Mycobacterium marinum on the basis of acid-fast (Ziehl–Neelsen) staining, molecular identification, and phylogenetic analysis. Histopathology revealed granulomatous lesions at various stages of development, and the necrotizing granulomas contained numerous rod-shaped bacteria that stained positively with acid-fast staining. This study revealed that M. marinum 2HYL117 is the pathogen causing mycobacteriosis in P. scalare in freshwater environments and can induce white nodular lesions through the formation of infectious granulomas.