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10.2.7. Cryptobia

10.2.7. Black-Strip Disease in Fish
10.2.7. Cryptobia in Fish

There is a ciliated protozoan that attacks cichlid fish internally. It is called Cryptobia. There are many species of cryptobia with considerable differences in how they present themselves. The organism is a small flagellated organism very similar in appearance to Hexamatadea spironucleus (hexamita, the cause of most bloat and dropsy).

Cryptobia was first recognized as a freshwater tropical fish disease only in 1990. Various cryptobia species are poorly studied and poorly understood. It is largely a disease of cichlids. Think of this disease when one has some of the symptoms of environmental mycobacteriosis (“fish TB”) coupled with significant cichlid deaths over a week or two (“fish TB” is much slower).

In the summer of 1995, there was an outbreak of the systemic form of Cryptobia in cichlids at the Chicago Shedd Aquarium. The outbreak resulted in the loss of 50% of the collection of cichlids. The organism has also been implicated in several die-offs at discus breeding facilities.

Cryptobia is probably quite common, especially among cichlids. But the deadly form of the disease has no clear symptoms and typically cannot even be found with a microscope. So when one has some unexplained cichlid deaths this might well be the cause. Since there is no treatment the discussion is academic in any case.


Cryptobia can be systemic in the fish’s bloodstream and cause a rapid decline in large numbers of cichlids in an aquarium. Mortalities associated with the systemic form may exceed 50% of the infected population.

The sick fish typically stop eating. Then they become progressively more listless and they withdraw from contact with other fish. They become stationary and their respiration rate will increase dramatically, largely because the disease has destroyed their red blood cells. Then they die in one or two days.


This disease is generally ONLY seen where the hobbyist is following the common misconception that all is well if the ammonia and the nitrite in the water column are both zero, i.e. “The water parameters are good”. This is simply not true. Cryptobia is generally not a problem in aquariums which have over-filtered, crystal clear, bacteria-free water.


The Key to Good Fish Health is Clean, Clear,  Bacteria Free Water


Note this does not mean water which is changed frequently.  The idea that water changes create good health is a myth. The idea that water that has “good water parameters” will give good health is also a myth. Typically, to get crystal clear, bacteria-free water one must use 20 times more biofiltration than ammonia oxidation requires. Ammonia oxidation is easy. Clear water can be difficult

There are no medications hobbyists can obtain for cryptobia. So treatment for cryptobia, like treatment for mycobacteriosis (“Fish TB”), consists of adding copious amounts of good filter media and filtration. This over-filtration reduces the bacterial count in the water. Since fish no longer have to fight off infections from all the bacteria in the water, the fish have far more immune system resources available to fight off diseases like cryptobia.

The bacteria count is related to the number of square feet of biomedia filter media surface available to the water flow in a filter. The very rough rule of thumb is:


One Pound of Fish Needs 100 Square Feet of Biomedia Surface Area to have Crystal Clear Healthy Water


Follow this rule and the home hobbyist will rarely see cryptobia or any other fish disease.

Other Cryptobias

There are 52 species of Cryptobia known from fish. 40 of these live in the blood, 7 in the gut, and 5 on the body surface.

Examples include:

  • Cryptobia branchialis, an ectoparasite that lives on the skin or gills. It can deform the skin and cause anorexia and death.
  • Cryptobia iubilans, an endoparasite that lives in the intestines and causes granulomatous inflammation of the abdominal organs, resulting in weight loss and death.
  • Cryptobia salmositicaC. borreli, and C. bullocki are blood parasites that lead to anemia and lesions in the haematopoietic tissues.

These cryptobia are probably the cause of many “unexplained” deaths in fish. But since there is no treatment beyond over-filtration and UV, the discussion is kind of academic.

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