Affected fish

All species, Anabantoids (including Gouramies) are particularly prone and it is often seen in Dwarf Gouramies (Colisa lalia)

Cause

Caused by a group of bacteria known as Mycobacteria which often thrive in mulm and debris. Fish can ingest the bacteria by scavenging in affected substrate, through wounds, or by eating infected bodies. Once infected, symptoms may not be visible for several weeks

Symptoms

Once established, the bacteria triggers inflammation and the fishes immune system surrounds the area with white blood cells which causes clumps known as granulomas to form. Depending on where in the body granulomas form, symptoms can vary significantly. Build-up of body fluid (dropsy), abnormal behaviour, wasting, ulcerations, and protrusion of eye(s) are all possible symptoms

Prevention

Regular gravel cleaning and good mechanical filtration will help to keep organic background levels down and reduce the bacterial population. Never feed predatory species live fish, apart from being nutritionally inadequate, it is cruel and will aid in the transfer of disease.

Treatment

The disease agent, mycobacteria, is resistant to proprietary treatments and effective treatment can only be obtained with expert administration and expense. To prevent the spread of infection it is best to euthanase heavily affected fish. Since the visible symptoms of the disease are also seen in many other problems, treat for these first and consider euthanasia as a last resort. Susceptible species should be avoided if you suspect your aquarium has mycobacteria present.

Notes

Fish tuberculosis can also infect humans, usually through cuts in the skin, so care should be taken if you suspect an outbreak.