ABSTRACT
Acid-fast staining bacteria were first discovered as fish pathogens in carp in Europe during the latter part of the 19th century. Members of two genera of acid-fast bacteria cause infections in fish: Mycobacterium and Nocardia. Mycobacteriosis is an infrequently encountered disease of fishes that is usually chronic and terminal. Gross external clinical signs of mycobacteriosis vary depending on the species of fish. Mycobacteriosis is routinely diagnosed by detection of acid-fast staining bacteria in smears from nodules or histological sections of the tubercles but it is difficult to differentiate Mycobacterium from Nocar dia in histological sections. Mycobacteriosis is chronic disease that results in low morbidity and moderate to high cumulative mortality. The disease usually develops more rapidly in warm water. Infections of Nocardia, "nocardiosis", in fish are difficult to distinguish from mycobacteriosis because both are acid-fast staining organisms and the resulting lesions are overtly very similar. Two bacterial species are known to cause nocardiosis in fish: N. asteroides and N. kampachi.
