2-10-2019, 15:49
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Mycobacteriosis, or fish tuberculosis, is a disease that is difficult to detect and therefore often diagnosed rather late.

Mycobacteriosis is common throughout the world. All fish species should be considered susceptible to the disease. Some are more susceptible than others, e.g. gourami and neon tetras.

Clinical signs

Mycobacteriosis is a chronic, progressive disease. The infection can take years to develop into a clinically distinct disease.

Some signs to look out for are:

  • lethargy
  • anorexia
  • loss of fins and scales
  • exophthalmia
  • emaciation
  • inflamed skin
  • oedema
  • peritonitis
  • nodules in the muscles, which may deform the body of the fish

Examination usually shows gray or white nodules in the liver, kidneys, heart or spleen. There may also be skeletal deformities. Diagnosis is usually based on clinical signs and the presence of acid-fast bacteria in tissue sections.


Mycobacteria are gram-positive pleomorphic bacilli, which are acid-fast and not motile. They form creamy or yellow colonies on solid media. It has been suggested that transmission of this disease may be caused by contaminated food.

Mycobacteriosis bacteria can often be found in mud and mulm that accumulate at the bottom of water bodies. Mycobacteria are the smallest organisms capable of reproducing themselves.

The usual way of infection is through the mouth, when fish take food from the substrate, or eat contaminated prey or carcasses. Mycobacteria then penetrate the stomach walls, causing an inflammatory reaction. In addition, infection can occur through cuts and abrasions on the body. The bacteria can live in both fresh and salt water.

The best temperature for the growth of mycobacteria in fish is around 24 °C, and the average incubation period before clinical signs appear is about six weeks. In the face of infection, the fish's immune system will try to contain and destroy the mycobacteria by surrounding it with white blood cells. These clusters of cells can be seen with the naked eye in infected fish and are called granulomas. They usually look like grey-white nodules and can be found in various organs. Unfortunately, such self-protection is partly successful. If one such granuloma enters a blood vessel, mycobacteria can be transferred to any internal organ of the victim.


Kanamycin + Vitamin B-6 for 30 days is the most effective tuberculosis treatment known to us. Infected fish must be placed in a quarantine tank for the duration of the treatment. It must be said that liquid children's vitamins, sold at your local pharmacy, are a good source of vitamin B-6. One drop for every 20 litres of aquarium water is sufficient.

An infected aquarium should be thoroughly cleaned. In some cases, all soil, plants and decoration that cannot be properly cleaned and sterilised may have to be disposed of. The fact that the disease is potentially infectious for humans raises the question of whether we should treat infected fish at all or whether humane euthanasia is still the most appropriate solution.

Dirty aquarium water, overcrowding and poor quality food are the main causes of this disease. To prevent this infection, all newly purchased fish must be quarantined. Timely isolation of sick fish will avoid greater problems in the aquarium.

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