Flavobacterium columnare

From Fish

Flavobacterium columnare formally known as Flexibacter columnaris as well as Bacillus columnaris, and Cytophaga columnaris. This is a common gram-negative bacteria which gives the appearance of white fungus on fish but is actually a bacteria. Its name is derived from columnar shaped bacteria, which are present in virtually all aquarium environments.

If left untreated it is usually fatal and is highly contagious. A tank that has had columnaris in it should be completely restarted and cleaned out after an outbreak if all fish have been lost. This disease can be spread easily between tanks from contaminated fish nets, your own hands if they have not been washed in-between tanks, shared containers and even food.

Other names

Columnaris, Cotton-Wool, Cotton-Mouth, Flexibacter, Mouth-Rot, Flavobacterium Columnare, Saddle Back, False Neon Disease, Guppy Disease.


Columnaris is partly caused by bad water quality, allowing uneaten food to remain in the tank causing this bacteria to multiply, as well as the fish having an inadequate diet or stressed from being introduced to a new tank. Wounds and injuries can easily become infected by this opportunist bacteria.


Symptoms of this condition are as follows:

  • Off colour patches appear on body
  • Lesions around the dorsal fin and body
  • White banding around dorsal area
  • Rapid breathing
  • Cotton-wool-like mouldy growths around the mouth, similar to Mouth Fungus
  • Swelling of the kidneys, behind the gill/throat area
  • Fin and Tail Rot
  • Stringy Fungus appearance around the affected skin, often misdiagnosed as Fungus not Columnaris
  • White spots around the head, edges of fins and scales



  • 20% weekly water change, good biological filtration, maintaining good water quality, include vacuuming the substrate, keep tank well aerated, varied diet and not overstocked.

In order to rid your tank and fish of this disease:

Category:Bacteria treatments/Commercial treatments1

  • Sterilise any infected equipment etc as Columnaris can spread through contact


  • Regular water changes.
  • Do not over feed or over populate the tank.
  • Fitting a UV device to the tank will help to keep the overall levels of bacteria down.
  • Setting up a tank with a natural soil-based substrate will suppress the levels of this bacteria down.


  • Dr. Barb - Flipper & Fins