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Tropical Fish Diseases – Columnaris

This is a highly infectious disease predominantly affecting live bearing tropical fish amd is caused by the bacteria Flavobacterium columnare. It is mainly caused by extremely poor water conditions and the introduction of new fish into the tank. Columnaris symptoms are:

  • Gray/white patches in a ‘column formation’ either ascending or descending on the body of the fish
  • Gray/white patches around its mouth
  • Damaged, deteriorating fins and tail.

During a later stage of Columnaris a fish’s gills may get affected, symptoms are:

  • Gills becoming ulcerated and sore
  • Sores will start appearing all over the body.
  • The fish will keep it’s fins very close to the body and will not be spreading them at all


Columnaris Symptoms
Columnaris Symptoms


It is always a good idea to isolate new fish in a clean separate tank for about 2 weeks before introducing them into a main tank to prevent onset of Columnaris. In the early stages, a good universal anti-bacterial medication will be able to recover the fish to full health. As with all diseases we at Aquascope always recommend isolating diseased fish to a separate tank until they are at full health again just so the other fish in the tank are at less risk of catching a disease. At later stages of the disease, especially when the gills become affected, the internal organs of the fish will become infected and this is usually fatal unless antibiotics are administered in addition to the anti-bacterial medication.

For the early stages of Columnaris we recommend using API Melafix anti-bacterial solution (see link below).

For the late stages of Columnaris when the gills start to become ulcerated and sores appear an antibiotic must be administered to the fish, we recommend Fish Mox Forte Amoxillin capsules.


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  1. i thought this information is very helpfull < is this the same with any normal fish like goldfish,thank you very much for the help .

    • Hi Chloe,

      Yes, you can use the same Interpet solution to cure Columnaris in goldfish too. Generally there’s not much difference between treating disease in tropical and coldwater fish.


  2. Thank you! I had quite a time finding a good description of what is affecting one of my guppies. Already had Mal on hand, started dosing right away.
    I had to do an emergency transfer to a brand new uncycled aquarium when my pond was contaminated. My fish are doing good though for the trama and the cycle is advancing surprisingly well. This is one less crisis.

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