Illness and Disease Fish Tank Guides

Columnaris in fish – Fish illness and disease

columnaris in fish

Columnaris is a common illness in aquarium fish, often referred to as ‘cotton wool disease’, amongst other names, columnaris in fish causes various symptoms and can be very deadly to your aquarium pets. Here we take a look at columnaris, its symptoms and some recommended treatments to help eradicate it.

Columnaris in fish

Columnaris is a fairly common illness to affect our aquarium fish. There are many strains of this disease that are caused by bacteria that create column-like structures, hence its name.

Columnaris attacks the gills and can often cause the appearance of thin white ‘fluffy’ patches on the fish’ body.

These white patches usually begin at the base of the fin and spread both up the fins and around the body as the illness progresses.

Due to the appearance of the disease, columnaris is often referred to as; cotton wool disease, mouth fungus, saddleback disease and many others.


Columnaris disease

Columnaris disease is caused by the slender, motile bacteria Flavobacterium columnare.

The disease can be quite fatal to aquarium fish as it attacks the gills and is thought to affect cardiac output. Mortality rates as high as 90% have been recorded.

Columnaris is found worldwide in both tropical and temperate water fish, it cannot survive in saltwater.

Columnaris is very easily transmitted between fish and is thought to affect all species of freshwater fish. It regularly infects populations of salmon as they make their way upriver.

The causes of Columnaris disease are often stress-related. Fish affected by stress are far more susceptible to illnesses of all kinds, this being no exception.

Overcrowding, poor water conditions, netting and disputes with tank mates can all cause increased stress levels which makes your fish more prone to contracting an illness.


columnaris in fish


Columnaris appearance

On first appearance, columnaris is often confused with Epistylis or white spot disease, also known as Ich. However, the white/yellow/brown-ish, cotton-like patches caused by columnaris will soon grow larger, identifying it as columnaris.

Columnaris is another reason why temperature treatment against Ich is not recommended. The two are are often confused and whilst increased temperatures do not actually kill Ich, many aquarists still opt for it as their preferred treatment.

However, increased temperatures reduce the amount of dissolved oxygen in the water, with a columnaris infection of the gills this could prove to be a deadly combination.

Columnaris can withstand temperatures of 37°C+, it cannot be treated by heat.

Columnaris is also easily confused with Saprolegnia, the two both produce white/yellowish cotton-like patches on the fish’s body, but Saprolegnia is not reported to attack the gills of the fish.

Saprolegnia is a fungal infection, it presents similar symptoms but can be distinguished by the height of the cotton-like growths.

Columnaris only presents a thin layer, Saprolegnia will grow upwards, looking almost like a cotton ball stuck to the fish.


Diagnosing Columnaris disease

Diagnosing columnaris disease can initially be quite difficult. As I stated above, it is regularly confused with other illnesses which can present similar symptoms.

Columnaris often presents as whiteish patches on the fish’s body and/or fins, it also causes the fins to fray allowing further infections to enter, such as fin rot.

These whitish patches are often more noticeably yellow or red around the edges. This is due to a larger presence of bacteria in these regions.

As the whitish patches develop, they may appear cotton-like, almost like part of a cotton wool ball has been attached to the fish.

Columnaris often attacks the gills, this is what makes it fairly deadly. As it attacks the gills, the gill may become pale as the tissue dies.

If left untreated, the fish’ gills will eventually be destroyed, leaving the fish unable to take on oxygen.

Columnaris is often accompanied by fin rot and/or mouth rot, causing cotton wool-like infections on the fish’s mouth too.

If left untreated, affected fish may begin to lose scales from infected areas, these bacteria can progress through the epidermis and leave muscle and other tissues exposed to the elements.

The sooner that Columnaris can be identified, the better. Columnaris spreads quickly and in some cases can cause a fish’ death in under 24 hours, maybe even less.


columnaris in fish


Treating Columnaris

Columnaris disease can be difficult to treat, mostly as many of the treatments are not suitable for all aquarium inhabitants.

In advanced stages, anti-microbial foods may be required. As the Columnaris exposes the muscle tissue of the fish, it is common for septicemia to infect the fish too.

Potassium permanganate is said to be effective in treating external columnaris. This is best used as a bath treatment but may also be added to the aquarium.

NT labs produce a medication called Permanganate which is for this exact purpose:


Medication containing copper-sulphate has also been shown to be effective against Columnaris disease. Copper sulphate is deadly to inverts and to some sensitive fish (scaleless).

Terramycin or Oxytetracycline has been shown to be effective in treating both the external infection and for use in medicating food.

Seachem Cupramine looks promising as a remedy, but as above, it is not deemed safe for inverts or scaleless species. They will need to be removed prior to treatment.

(As an amazon associate I earn on qualifying purchases).


Terramycin is said to be ideal as both an external treatment and as a suitable addition to the infected fish’ food. Unfortunately I have been unable to find a product that contains it that is listed as fish safe, so I cannot recommend one.

Acid baths have shown to be very effective against columnaris, but unfortunately, it is usually fatal for the fish too, so treatment options remain fairly limited.





Columnaris disease in fish: a review with emphasis on bacterium-host interactions – Declercq, A.M., Haesebrouck, F., Van den Broeck, W. et al. Columnaris disease in fish: a review with emphasis on bacterium-host interactions. Vet Res 44, 27 (2013).

Treatment of columnaris disease of rainbow trout: low pH and salt as possible tools?

Wikivet – Columnaris Disease

Bruno DW, VanWest P, Beakes GW. Saprolegnia and other oomycetes. In: Woo PTK; Bruno DW, ed. Fish Diseases and Disorders: Volume 3: Viral, Bacterial and Fungal Infections, 2nd Edition. Wallingford, UK: CABI International, 2011, pp.669-720.

About the author

James @Seriously Fishy

I am a fish keeping enthusiast with over 20 years experience. I currently keep American Cichlids (CA) which are my favourite fish to keep so far. I started Seriously Fishy as I noticed a large volume of people on various web pages looking for help with Aquarium basics. I created the first Seriously Fishy book to solve the issue in 28 pages, that led to the Seriously Fishy UK fish forum and blog.

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