Mycobacterium marinum is a slow growing fresh and saltwater mycobacterium (SGM) belonging to the genus Mycobacterium and the phylum Actinobacteria. It was formerly known as Mycobacterium balnei. The strain marinum was first identified by Joseph D. Aronson in 1926 and it is observed as a pathogenic mycobacterium causing tuberculosis-like infections in fish (mycobacteriosis) and skin lesions in humans. The bacteria grows optimally at a temperature around 30 °C.