Mycobacteriosis ("piscine tuberculosis" or granuloma disease) is an important chronic, systemic bacterial infection of fish. Infections have been reported worldwide from over 150 different species of marine and freshwater fishes representing 40 piscine families. These organisms also have a documented zoonotic potential for humans, especially in immunosuppressed individuals. Therefore, an outbreak of mycobacteriosis in an aquaculture or home aquarium system presents a serious problem for both the personnel handling and processing infected fish and the home hobbyist. Infections of fish in home aquarium systems are generally thought to he disseminated through the aquarium environment and to other fish by the death of an infected individual resulting in the release of the infectious organism into the water. However, histopathological evaluations of several recent clinical submissions of various species of tropical have suggested that mycobacteriosis may also be spread through the release of reproductive material during spawning.