Flavobacterium columnare

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About Flavobacterium columnare (Mouth Rot)

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.

This is a quick acting disease and needs immediate treatment. Be aware that some strains of this bacteria are becoming resistant to antibiotics. So ensure you treat for the full length of the medication.

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

Commercial treatments

King British


  • No.8 - Anti Fungus and Fin Rot
  • No.10 - Methylene Blue
  • Catalogue


Pets at Home

  • Disease Treatment (contains Protargol 0.151% w/w (Silver proteinate) [3]

API (Aquarium Pharmaceuticals)

Tetra UK

Tetra USA

  • Lifeguard™ All-in-One - Kills bacteria, fungus and parasites.

Jungle Labs (USA)

  • Lifeguard - All-in-One - Kills bacteria, fungus and parasites (contains HaloShield (1-chloro-2,2,5,5-tetramethyl-4-imidazolidinone))
  • Anti-Bacteria Medicated Fish Food - for bacterial Infections (Mouth rot)
  • Binox (Crystal) Broad range anti-bacterial and Fungus treatment contains Nitrofurazone <9%. See MSDS)


  • TRICIDE-Neo™ - Antibacterial Dip - a concentrate of NeoMycin antibiotic [4]


  1. Dr. Barb - Flipper & Fins
  2. 2.0 2.1 2.2 2.3 Veterinary Medicines Marketed under the Small Animal Exemption Scheme, VMD
  3. 3.0 3.1 Chemical information on the product
  4. Tricide Neo tris-EDTA Solution Against Bacterial Infections
  • 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. See Walstad.


External links