Fish mycobacteriosis is a chronic granulomatous disease caused by several species of bacteria from the genus Mycobacterium, described as nontuberculous mycobacteria (NTM). The most important species causing fish mycobacterioses are M. chelonae, M. fortuitum, and M. marinum. Mycobacteria infecting fish also include zoonotic pathogens. M. marinum is the cause of most cases of fish-related mycobacterial infection in humans. The disease occurs more frequently in workers in the fishing industry, people whose hobbies involve water activities, and aquarists. The aim of the present study was to examine the occurrence of different species of mycobacteria in freshwater ornamental fish.The occurrence of Mycobacterium spp. in freshwater ornamental fish was studied from January 2015 - December 2016. Material isolated from skin scrapings, contents of the digestive tracts, and internal organs of ornamental fish was stained with Ziehl-Neelsen (ZN) and inoculated on Lowenstein-Jensen medium. All isolates found positive by ZN were identified by amplification of the gene encoding the Hsp65 protein. A total of 408 samples obtained from 136 ornamental fish from 36 species were tested.Using the culture method Mycobacterium was isolated from 69 fish (50.1%) and 99 samples (24.3%). Sequence analysis of gene fragments coding for the Hsp65 protein of 99 isolates revealed occurrence of 13 species of mycobacteria: M. abscessus, M. chelonae, M. fortuitum, M. gordonae, M. marinum, M. mucogenicum, M. neoaurum, M. peregrinum, M. salmoniphilum, M. saopaulense, M. senegalense, M. septicum, and M. szulgai.The obtained results indicate a significant role of ornamental fish as a source of mycobacteria which are potentially dangerous,especially to humans.