Columnaris Disease - What what causes it & how to treat it.

Columnaris Disease


Aquarium hobbyists who take extra care looking after fish and the environmental conditions rarely will encounter fish diseases, however, there is no guarantee your beloved fish will not get sick. It is important to have stable water chemistry, perform frequent monitoring of behaviour and look out for any signs and symptoms of aquatic diseases.


What is it & what causes it?

Also often called cotton mouth disease, cotton wool disease and saddleback disease, it is often mistaken for a fungal infection, however, it is a common bacterial infection. It is highly contagious and usually ends up killing the fish, do not worry it is only contagious to fish. It affects all freshwater fish, especially livebearers such as guppies, platies and endlers. Generally, any fish bred in large numbers are more prone to becoming infected.  

It is caused by a microscopic Flexibacter bacterium called Flavobacterium columnare. They are present where an aquarium has a high content of uneaten food and other waste products.  Any stressful conditions such as overcrowding, injury, unstable pH, poor water quality and a poor diet also can cause an outbreak in your aquarium.



Ulcerations usually develop in the first 24 to 48 hours, followed by fatality within 72 hours, hence if any symptoms are present, treatment must start right away.


  • Cotton growth near mouth and gill filaments
  • Frayed and ragged fins
  • Ulcerations on scales
  • Epidermal loss
  • Mucus on gills, head, and dorsal regions
  • Colour changes


  • Breathing rapidly & laboriously
  • Loss of appetite
  • Rubbing body against objects in the aquarium



Unfortunately, with columnaris, your fish may be too weak to respond to treatment. You can try every possible treatment below, but as this disease is so fast to kill fish it will not guarantee the survival, although it will give them the best fighting chance.

If possible, always treat sick fish in a separate tank and quarantine them. As soon as you see any of the above signs and symptoms you must start the treatment for your fish right away. Remove any dead fish immediately and in severe cases, the whole aquarium must be treated.

Firstly, try to improve water conditions and lower the temperature in the aquarium to 24°C (only if fish can sustain this change, if not remove prior and use a better suited method). When decreasing the temperature do so slowly as fish are sensitive to dramatic changes.

Use commercially available antibiotics that treat gram-negative bacteria (oxytetracycline, kanamycin and nitrofurazone are recommended). Copper sulfate, terramycin and hydrogen peroxide can be added externally but be sure to control the concentrations as it can be lethal to the fish if too high.

Increase salt concentration particularly when livebearers are infected, the bacterium cannot survive when salt content is greater than 1%. Mix 1-3 tsp per 4 litres. This process should not be used on salt-sensitive fish such as catfish.

Medicated food can be used containing oxytetracycline. This treats any internal infections the fish may have. As columnaris is highly contagious, it can be transmitted through contaminated nets and even food, therefore sterilising equipment is important during treatment so it is not spread to other aquariums especially if any filtration systems are shared in your home. You can soak equipment in a solution of 3% hydrogen peroxide and rinse with non-contaminated aquarium water.


Most likely the bacterium is already living in your aquarium waiting to attack when the fish have a weak immune system and become stressed.

As with any fish diseases, combatting any stress should be your top priority. Stress comes from many factors, not just parasites themselves. Always ensure you have the best water quality conditions in your aquarium, check equipment regularly and carry out any maintenance if needed. Never overcrowd your tank as this increases stress and aggression. Perform water changes regularly and cycle your aquarium.

When purchasing new fish, place them into a quarantine tank to prevent the spread of diseases to their new friends. Remember to disinfect any equipment that could have been contaminated.

Always feed your fish with the best species-specific food so their immune system does not become suppressed. Be familiar with the signs and symptoms so you can recognise the disease early. This is one of the nastier diseases, but if you catch it early on and treat it correctly your fish should fight it. If your fish do not survive the outbreak try not to beat yourself up, you tried everything, but they may have been infected with the faster strain.

Using the product Super Fix (which can be purchased here online) has shown promising effects against columnaris disease. This product contains anti-mutagenic, DNA protecting properties which improves the immune system, assists in self worming, reduces stress of display stock, and can reduce fish loss. It contains locally sourced ingredients and is safe to use with a variety of aquatic fish, plus it can assist fish with many other known aquatic diseases. Head on over to the shop or product info tab to check it out!

Thank you again for reading, we hope to see you again, take care!