Understand Flexibacter Columnaris Betta Fish Diseases

Flexibacter Columnaris is also known as the following:

  • Cotton mouth
  • Mouth fungus
  • Cotton wool

Because of the mould lesions, Flexibacter is often mistaken for a fungal infection, but is actually a bacterial infection found commonly in cultured fish. Present in virtually every aquarium, it is of a columnar shape, it is this shape that got it its name. 

Fish are prone to bacterial infections because of many reasons. Some of them are:

  • Stress caused by poor quality of water
  • Bad handling when being shipped
  • Bad or poor diet

The Flexibacter enters the fish through its mouth and gills or if it has any, through a tiny skin wound. It spreads wildly on the nets; food and holding tanks etc., and is very highly contagious. Lesions appear slowly in chronic cases and can take days to kill the fish. It can spread throughout your fish population rapidly killing them all. This can happen within a few hours. The disease is more prevalent in higher water temperature. Alas lowering the temperature will do nothing to prevent the end result.

When fish are stressed by poor water quality, poor diet, or even handling and shipping, they become prone to bacterial infections. Columnaris enters the fish through the its gills, mouth, and even through small skin wounds. The disease can spread rapidly in nets, holding containers, food or any number of other means. It is highly contagious.

Symptoms externally:

  •  Appearance of white spots on the mouth and edges of scales and fins
  • The whites spots turn into lesions of a Brownish/yellow, sometimes with a red tinge.
  • A growth will form on the mouth, the infected area will be eaten away by the growth. The growth has the appearance of cotton (mouldy).
  • There is a wearing away (erosion) of the fins from the edge inwards.
  • A lesion will form in the area near the dorsal fin.
  • Fungus will appear on the affected skin
  • The gill filaments will erode and begin moving very fast trying to gain more oxygen.


Sometimes less commonly the fish gets attacked by the bacteria internally, if this happens there are no symptoms.

  • If you see any of the symptoms above, change the water frequently and clean the decorations such as gravel etc.,
  • When changing the water (once a week or when water gets cloudy) add a quarter of a teaspoon of AQUARIUM SALT (not table salt). This prevents the build up of methemoglobin.

Always stock up your aquarium slowly and never over-feed the fish. Remove all uneaten food from the water after 5 minutes. Under normal circumstances your tank only has to be tested for ammonia twice monthly. If your filter stops working test for ammonia within 24 hours to make sure that the good bacteria that eliminates the wastes are still unaffected. Whenever one of your fish seems to be ill you must test immediately for ammonia, simply to rule out ammonia poisoning. Your tank must be cleaned and changed at least once a week or if the water becomes cloudy.

During the treatment, discontinue carbon filtration and treat with cooper sulphate, antibiotics and chemicals (Terramycin, Furan and Acriflavine). It will be a good idea to speak to your pet store manager as to these products. Terramycin is used for treating the foods for infections that are internal. If you are treating Catfish, be careful as they are very sensitive to salt.

If you follow these steps, you can reduce the chance of your betta getting fin rot or Flexibacter Columnaris:

  • When you purchase new fish, you should quarantine them for at least 2 weeks (disease can be prevalent in pet stores).
  •  Make sure the tank water is kept fresh and clean
  • Make sure the fish are fed on a well balanced diet
  • Before using any equipment make sure it is well disinfected in order to stop the chance of spreading bacteria

Using these steps to health you will also reduce stress in your fish. Stress is the largest contributor to disease in all animals including humans.

Maintaining a good diet and looking after the water will generally keep your fish healthy and stop them from becoming stressed, reducing their susceptibility to infections being stressed and therefore reduce its susceptibility to infection.