Fish tuberculosis (TB) is something very similar to that which can infect humans. In Fact, there are several different types of TB causing bacteria in the same genus, including that which is known to cause TB in man.
The bacteria which causes fish TB is known as Mycobacteria marinum. Luckily, fish TB is not very contagious, and as a result, if symptoms are noticed early, it will not have an effect on the other life in the aquarium. Symptoms include the following:
loss of appetite
fish remains in seclusion and out of site
rapid breathing (respiration)
eyes appear to be cloudy or "popping out"
fish lies on its side near bottom of aquarium
stomach of fish appears to be sunken
whittish blotches on exterior
degraded and frayed fins
The fish can last for weeks with these symptoms, often allowing for detection and treatment before permanent effects are caused. Although this disease is not very contagious, it is a good idea to remove the fush from the main aquarium into a treatment tank. This disease slowly degrades the health of the fish by depositing small "tubercules" on many of the major internal organs of the fish.
Treatment of fish TB is rather difficult since it effects the internal portions of the fish. The best way to treat it is to prevent it by keeping a balanced diet for you fish, and making sure that the quality of the environment in your aquarium is good. If you are unlucky enough to have to treat TB, the infected fish should be placed in a separate treatment tank. 40 grams per gallon of streptomycin and isoniazid, each, should be added to the treatment tank. Treatment can be increased by adding streptomycin to food. There are several other diseases which can be mistaken for fish TB. The best plan is to be overly careful. Monitor the fish closely, and check for the symptoms listed above. While treatment of this disease is possible, the best plan is to keep the quality of the fish's environment as clean as possible. This will reduce the chance of fish infection with TB, as well as decrease the chance that other bacterial and fungal sicknesses will overcome your fish.