Tuberculosis

It has not been generally appreciated in the past that tuberculosis is one of the most common causes of disease and death in aquarium fishes. This disease is the great imitator - it can appear as ulcers, pop-eye, dropsy, rectal prolapse, or simple malnutrition with progressive thinning and deterioration. In some cases fish can actually appear more colorful although less active just before they die from the infection. The causative organisms can be restricted to the skin or muscle in ulcers, or may be widespread throughout the internal organs. An amazing number of organisms can be present before obvious symptoms appear, so it is unfortunately easy to acquire an infected fish which appears to be healthy.

More than one species of bacteria can cause this disease in fish. They are called "acid-fast" bacteria because of special staining characteristics. They are difficult to stain with certain dyes but resist decolonization with acid. A human disease known as "swimming pool granuloma" is similar to the ulcer type of fish tuberculosis. The name indicates where the disease is usually acquired, generally as the result of a swimmer scraping himself on the side of a contaminated pool. The condition is not serious in humans, and consists only of a slowly healing sore on the skin. It never progresses to the internal organs. For practical purposes the fish disease is not transmittable to humans.

There is no satisfactory treatment for this condition in fish. The usual antibiotics which are effective against human tuberculosis seem to have little effect against the fish disease. An infected tank is also very difficult to sterilize after the sick fish are removed. The affected fish should preferably be destroyed and the contaminated tank disinfected and sterilized.