Hepper is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Columnaris in Betta Fish (Cotton Wool Disease): Vet-Approved Signs, Causes, Treatment & Prevention

Lindsey Stanton Profile Picture

By Lindsey Stanton

sick betta fish

Vet approved

Dr. Luqman Javed Photo

Reviewed & Fact-Checked By

Dr. Luqman Javed

DVM (Veterinarian)

The information is current and up-to-date in accordance with the latest veterinarian research.

Learn more »

While columnaris is certainly an unsightly and worrying condition to find in your Betta fish, it is treatable (provided you act fast). That said, prevention is always better than the cure, and understanding the ways to prevent the disease is as important as knowing how to treat it. In general, Bettas are hardy, resilient fish that can live happy and healthy lives as long as they are provided with a clean tank, a balanced diet, and optimal water parameters.

In this article, we look at what exactly columnaris disease is, what causes it, how to treat cotton wool disease in your Bettas, and how to prevent it. Let’s get started!



What Is Cotton Wool Disease?

Columnaris goes by several different names, including cotton wool disease, cotton mouth disease, and saddleback disease, and it is a fairly common condition among freshwater aquarium fish. Despite its cotton-wool, “fungal-like” appearance, columnaris is not caused by a fungus, but rather by a bacterium called Flavobacterium columnare. It can affect all species of fish in a freshwater tank, not just Bettas, so you’ll want to get rid of it as soon as it appears. Unfortunately, it causes death rather rapidly (especially in a tropical aquarium) and death usually occurs in 2-3 days if no treatment is attempted.

What Causes Cotton Wool Disease?

Flavobacterium columnare, the bacteria responsible for cotton wool disease, is so common that it actually lives in most freshwater tanks, unbeknownst to the owner. If your fish live in a healthy environment, with a healthy diet and strong system, they can live with the bacteria their entire lives without it affecting them.

That being said, small changes can cause infection in your fish, including:

  • Too many fish in your tank will place a burden on your filtration system that is too much for it to handle, resulting in poor water quality and the proliferation of potentially harmful bacteria.
  • Fluctuating water parameters. If your water temperature and pH levels do not stay stable, this can quickly stress your Betta fish out, which will naturally compromise their immune systems.
  • Introducing other fish too quickly, fighting, and fluctuating tank conditions will all cause stress to your Betta, resulting in a weakened immune system.
  • Poor diet. Since Bettas are carnivorous, feeding them the incorrect food or not enough protein will cause a weakened immune system.
sick betta in aquarium
Image Credit: Wirestock Creators, Shutterstock

Signs of Cotton Wool Disease

Columnaris is fairly easy to identify, although it can present itself in various ways on your fish. Other than the obvious cotton wool-like growth that shows up on your Betta’s gills (at which stage, the disease is already fairly advanced) there are several other identifiers of this disease, including:

  • Skin irritation. This is one of the first signs of the disease, and you may notice your Betta rubbing themselves against substrate or plants to try to relieve the irritation. Still, this kind of skin irritation may be caused by several other conditions, such as Ich or White Spot Disease, caused by a parasite. If your Betta’s skin irritation is accompanied by small white spots, it is likely not columnaris.
  • Color reduction. One of the first signs of an unhealthy Betta, no matter the condition, is fading colors. If you’ve noticed your Betta’s color losing its vibrance and they have turned somewhat pale or faded, this may be an initial sign of the disease.
  • Frayed fins. Not to be confused with fin rot, a disease that eventually affects the entire body of your fish, frayed and ragged fins are also one of the first symptoms of columnaris.
  • Small sores and ulcers may begin to appear, a sure sign that they have cotton wool disease and not fin rot.
  • Your Betta may become covered in a thin layer of mucus, which is the body’s attempt to rid the disease from its skin.
  • Swollen lips. Once the disease has progressed far enough, your Betta’s lips may appear swollen, and if left long enough, they will be permanently damaged. This will also cause a substantial reduction in appetite.
  • Inappetance. Your fish may eat much less and become lethargic. In advanced stages of the disease, your fish may not eat at all.



The 3 Steps for Treating Columnaris in Bettas

Now that you know the signs to look out for and the potential causes of cotton wool disease, let’s look at how to treat it effectively.

Step 1: Quarantine

The first step in the treatment of your Bettas is to move them to a separate quarantine aquarium. Bacteria thrive in warmer temperatures, so you’ll want the water temperature of your quarantine tank to be slightly lower than normal. Lowering the aquarium temperature to 75 °F (24 °C) is a must, since columnaris is much more virulent (causes quicker death) at higher temperatures, especially 85–90 °F (29.4-32.2 °C).

Step 2: Medication

Next, you’ll need to add a suitable aquarium antibiotic to your Betta’s quarantine tank. Antimicrobial medicine which contains nitrofurazone and kanamycin are the preferred options to treat columnaris. They should ideally be used together. There are several suitable medications to choose from, but API’s Furan 2 is a great choice as it contains nitrofurazone. KanaPlex contains kanamycin, which is a great adjunctive option for treatment. Simply follow the instructions on the bottle, or speak to a professional if you are unsure. Besides using an antibiotic, you can add aquarium salts, which will help reduce stress and boost your Betta’s immune system.

close up Mustard Gas Betta Fish
Image Credit: Dan Olsen, Shutterstock

Step 3: Water change

While your Betta is being treated in the quarantine tank, you’ll want to perform a full water change on their main tank. A 25% water change every day or two is a good way to rid the water of any remaining bacteria before you return your Betta and will give you a chance to thoroughly clean the tank and better the chances of your Betta’s recovery.

If you have caught the disease early enough and given your Betta treatment, they should recover quickly and easily. If they are not showing any signs of getting better, the disease may have progressed too far. Additional options can be discussed with your aquatic veterinarian in this case.

How to Prevent Columnaris in Your Aquarium

As the adage goes, prevention is better than the cure, and you’ll save yourself a great deal of time, money, and stress by doing your best to avoid your Betta getting the disease in the first place. While there are never any guarantees, here are simple methods that will go a long way in preventing your Betta from getting sick:

  • Don’t overstock your tank. It’s tempting to keep adding beautiful fish to your aquarium, but keeping too many fish in one tank can swiftly cause problems. All the fish in your tank produce waste, and your filtration system can only manage a certain amount. When your filter becomes overburdened, your tank’s water quality will get worse and worse, leading to the buildup of harmful bacteria.
  • Keep your tank clean. Your aquarium may look crystal clear from the outside, but it can still potentially harbor harmful bacteria. Keeping your tank clean and changing the water regularly will help prevent the proliferation of bacteria.
  • Quarantine new fish. Before adding any new fish to your tank, it’s important to quarantine them for a period first. This will allow you to see if they are sick and will limit the transfer of harmful bacteria to your tank.
  • Provide enough protein. Bettas are carnivores and thus need a great deal of protein in their diet. Making sure they have a balanced, nutritious diet suited to their species is essential in aiding a strong, healthy immune system to fight off infection.
  • Install a UV-light in your filter. Some canister filters have the option to add a UV light. This can help sterilize the water and clear it off excess free-swimming bacteria.



Final Thoughts

Cotton wool disease is a potentially deadly issue in freshwater tanks, so if you notice it in your Betta, you’ll need to treat it as soon as possible. Treatment is fairly easy, and if you catch the disease early enough, your Betta will most likely be fine. Still, prevention of the disease is easier than the cure. Making sure your aquarium is clean, changing the water regularly, avoiding overcrowding, and feeding your Bettas a nutritious diet will go a long way in keeping their immune systems healthy enough to fight off the bacteria.

Featured Image Credit: yin800321, Pixabay

Related Articles

Further Reading

Vet Articles

Latest Vet Answers

The latest veterinarians' answers to questions from our database