According to the literature (Chinabut 1999), fish tuberculosis is caused mainly by Mycobacterium marinum, M. fortuitum and M. chelonae. The diagnosis of aquarium fish tuberculosis is generally based on the histopathology, because there is seldom enough material for bacteriological culture due to the small size of the specimens. Big discus fi shes are an exception as tubercular granulomas in their organs can be seen at gross necropsy. Tuberculosis of fish is primarily an alimentary infection but bacteria also enter the body via gills and damaged skin. As a result of generalized infection, granulomatous changes, occur in the liver, spleen and other organs. Mycobacterial granulomas are morphologically specifi c and Ziehl-Neelsen staining reveals the acid fast bacteria in histological sections. We describe here the clinical signs and pathology of fish tuberculosis and its signifcance for humans.