hich are not members of the Mycobacterium tuberculosis complex (and M. leprae). NTM have a worldwide distribution as saprophytes in soil and in treated/untreated waters, where they can remain viable for over 2 years. NTM include many species of acid-fast bacteria, some of which are capable of causing chronic progressive diseases in mammals, birds, reptiles and fish. Thus, infected fish may be considered as primary reservoir for these pathogens and infection is probably acquired from NTM present in the environment by ingesting contaminated food or water containing organic matter, or through gill or skin lesions caused by trauma and parasites. Mycobacteria may cause cutaneous lesions or spread into internal organs through the circulatory or lymphatic systems. Transovarian transmission has also been documented in Siamese fighting fish (Betta splendens). All fish species should be considered susceptible to mycobacteriosis, with a higher prevalence in farmed animals and significant losses frequently observed in aquacultural activities. However, mycobacteriosis infections and mass mortalities in wild fish is not easy to recognized but see, because infected fish die and are easily predated or scavenged.