Tilapia Topic: Disease Vector Acid Fast Bacteria

Wild and cultured tilapia in Hawaii are often host to acid-fast bacteria. Although these infections are very common, attempts thus far have not been successful in the isolation and identification of the organism. Acid-fast bacteria are a unique group made up of several types of related organisms all of which share similar chemical properties of the cell wall, that are not shared by non-acid fast microorganisms. Because of this feature, these bacteria can be stained with a special tissue stain. This differential staining provides a means for recognizing the presence of these bacteria in tissues Mycobacterium and Nocardia. are two medically important genera of acid-fast bacteria. On the basis of morphology and negative results for culture of infected tissues on blood agar, we suspect that the organism involved is a Mycobacterium sp.

Acid-fast bacterial infection is usually subclinical in tilapia. Occasionally, illness in older, mature tilapia can be attributed to acid-fast bacterial disease. Some forms of multiple raised plaques or nodules of the skin are the result of tissue granulomas, the form of tissue reaction that is caused by acid-fast bacterial infection. Otherwise, infections can at times be recognized in the spleen as few to multiple, tiny, white-yellow nodules. Histological examination reveals these structures to be small granulomas which may contain acid-fast bacteria.

There is no effective or recommended treatment for acid-fast bacterial infection in tilapia. As a general management practice, older fish should not be held indefinitely as broodstock because of the possibility of increased occurrence of acid-fast bacterial disease in these fish.

See:

• Bacteria Vectors