Systemic Granulomatous Mycobacteriosis in Orbiculate Batfish (Platax orbicularis) Associated with Mycobacterium marinum-like Organism in an Aquarium in South Korea

In this report, we describe systemic granulomatous mycobacteriosis in an orbiculate batfish from an aquarium in South Korea. Gross examination of the deceased fish showed multifocal nodular lesions in multiple internal organs including the gills, spleen, and kidney. Histopathological analysis demonstrated severe chronic systemic granulomatous inflammation, and Ziehl–Neelsen staining highlighted abundant intralesional acid-fast bacilli. Molecular analysis based on partial sequencing of the 16S ribosomal RNA (rRNA) and heat shock protein 65 (hsp65) genes showed that the detected organism was most closely related to Mycobacterium marinum. Because the molecular analysis was performed using partial sequences obtained from formalin-fixed, paraffin-embedded tissues, definitive species-level identification was not possible. This case represents systemic granulomatous mycobacteriosis associated with a Mycobacterium marinum-like organism in orbiculate batfish in an aquarium in South Korea and emphasizes the need for continuous disease surveillance and improved diagnostic awareness of non-tuberculous mycobacterial infections in ornamental and public aquarium fish.