betta fish cotton wool disease
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What Is Cotton Wool Disease in Betta Fish?

When properly cared for, betta fish are hardy and thrive in captivity; however, they can become afflicted with illness when not properly cared for. One such disease is known as cotton wool disease. This disease is highly contagious and will kill your betta fish if left untreated. That’s why it’s important to know how to recognize and treat this disease, as well as prevent it from happening to your betta fish. 

What Is Cotton Wool Disease in Betta Fish?

Betta fish cotton wool disease is caused by a bacteria known as flavobacterium columnare. This disease is most often found in fish that belong to the anabantoids family, and is often seen in guppies. In fact, this disease also goes by the name “guppy disease.” Other names that this disease goes by include columnaris saddleback disease and cotton mouth disease. As this disease causes cotton-like growths on infected fish, it’s frequently mistaken for a fungus infection; however, fungal infections are uncommon in bettas.

What Causes Cotton Wool Disease in Betta Fish?

The causes of cotton wool disease can all be attributed to improper care of the betta fish, which means that this disease is completely preventable. Cotton wool disease can be caused by the following:

1. Bad Water Quality

Flavobacterium columnare is frequently found in aquariums with bad water quality. When there are high levels of nitrates and ammonia in the water, it can promote the growth of flavobacterium columnare. Ammonia and nitrates are unavoidable in aquatic environments as they are created by decaying fish waste, plants, or uneaten food. Also, ammonia and nitrate levels increase more rapidly when there are more fish than the tank size can handle.

It can be misleading to think that the water is clean just because it’s clear. Even clear water can have high levels of nitrates and ammonia levels. 

 Be sure to purchase a water test at your aquarium shop so that you can regularly test the water’s ammonia and nitrate levels.

2. Stressed Fish

As with any other animal, bettas become more susceptible to disease when they’re feeling stressed. Stress will lower the animal’s immunity against disease, making it more susceptible to infection from disease or parasites. Numerous causes can create stress, some of which include:

·         Unhealthy water quality

·         Sudden changes in water quality, such as temperature changes.

·         Feeling threatened by another fish.

·         Lack of a proper diet.

3. Low Oxygen Levels

Aquarium water that is not properly oxygenated can become a breeding ground for harmful bacteria species, including flavobacterium columnare. Try adding an air stone to the aquarium to increase the water’s oxygen levels.

Also, if you use a fishbowl instead of an aquarium, don’t fill the fish bowl to the top. Many fish bowls’ circumference (the distance around the bowl) narrows toward the top. By not filling the bowl completely, you’ll increase the surface area of the water. The greater the surface area, the more space there is for exchanging oxygen between the water and the air. 

4. Inadequate Diet

While bettas are mainly carnivorous, plant matter does make up a small portion of their diet. Not providing your betta a balanced diet can cause health issues. It could lead to a weakened immune system, making them more vulnerable to infections.

How Long Can Betta Fish Live with Cotton Wool Disease?

Cotton wool disease is highly contagious and can spread quickly throughout the aquarium. Additionally, the harm caused by this disease can take place quickly. For these reasons, we highly recommend that you start treatment as soon as you suspect your betta has been affected. Sick fish usually recover from this bacterium if treatment is started early enough, but if the disease is allowed to progress unchecked, it’s usually fatal.


Is Cotton Wool Disease Infectious to Other Fish?

Cotton wool disease is very contagious, with some strains being more contagious than others. Though it’s a disease mainly found in bettas and guppies, all species are susceptible. For this reason, you should always quarantine new fish before placing them with other fish.

What Are the Symptoms of Cotton Wool Disease?

Flavobacterium columnare affects other species besides fish. In fact, this bacterium can affect humans. In humans, this bacterial infection mainly affects the retina of the eyes. In fish, however, it can affect all body systems.

This disease goes through stages, so symptoms may not be visible in the early stages. Within the early stages, the betta’s color may fade and experience irritation. To relieve this, the betta may rub against objects in the fish tank. As the disease progresses, fin damage, ulcers, and skin growths appear. Further on in the disease process, the fish’s flesh may decompose, which normally leads to death.

Signs that your Betta has Cotton Wool Disease

The following are symptoms of betta fish cotton wool disease; however, it is important to note that many of these symptoms can be attributed to other diseases. For this reason, diagnosing your fish may require looking at what is happening with your fish overall rather than focusing on just one symptom.

Body Rubbing

Bettas will rub against objects in the aquarium to relieve themselves from body irritation. Body rubbing is one of the symptoms caused by diseases other than cotton wool. For example, the condition known as ich shows up as small white spots on the fins and body.

Loss of Color

A healthy betta will have vivid colors. If your betta’s colors are fading, it could be due to a number of factors, one of which is the early stages of cotton wool disease.

Frayed Fins

Frayed fins are an indicator that your betta is not well. A disease known as fin rot will eventually lead to the fin being eaten away. As it progresses, it will eat away at the fish’s body. In cotton wool disease, the fins do not disintegrate, but they’ll appear ragged or frayed.


The development of ulcers or sores on the betta’s body strongly suggests that it has cotton wool disease. Ulcers don’t appear on fish that are affected by fin rot.

Fluffy White Growths

The appearance of fluffy white growths on your betta’s body strongly signifies that your fish has cotton wool disease. These growths are not always white, as they can be yellow-brown or whitish-gray in color. These growths may appear as tufts, threads, or even saddle-shaped on top of the fish’s body. When this stage of the disease process has been reached, there may be additional symptoms, including a reddening around the growth area, sluggishness, and loss of appetite.

Necrosis of the Gills

In cases where the disease is allowed to progress untreated, flavobacterium columnare will make its way to the gills. When the gills are infected, they’ll lose their pink color and appear brownish. The color change is caused by necrosis, which is the death of the tissues. At this stage, the death of the fish is likely as it will have difficulty breathing.


In response to the flavobacterium columnare, your fish’s immune system secretes mucus that coats the fish’s body. The fish’s head, gills, and dorsal area are common places for this to occur.

Mouth Infection

At this stage of the disease process, the betta’s mouth swells, which will cause your fish to stop feeding as its mouth is rotting away. When this stage of the disease is reached, it’s too late for treatment.

Treatment for your Betta Fish with Cotton Wool Disease

Treating cotton wool disease is not easy, and the later the treatment is started, the less likely your fish will survive. For this reason, you should start treating your betta as soon as you suspect an illness. Furthermore, the treatment period for this disease is long. It can take up to a month to effectively treat your fish. 

If your fish is in a community tank, it will have to be isolated. The following are directions for setting up a quarantine tank for your sick fish or how to treat its current tank if your betta is kept alone.

1. Water Conditioner

If you’re setting up a quarantine tank, treat the tank with a water conditioner that will remove chlorine and other harmful elements found in tap water.

2. Water temperature

Flavobacterium columnare prefers warmer waters, so you’ll want to decrease the water temperature in the fish tank. Get the water between 75- and 77 degrees Fahrenheit. It’s important to lower the water temperature gradually so as not to stress your fish.

If you’re transferring your fish to the quarantine tank, make sure that you let it float in the tank for at least 15 minutes to acclimate to the cooler temperature. The combination of cooler water and drug therapy will help weaken flavobacterium columnare.

3. Antibiotics

The antibiotics Oxytetracycline, Maracyn, and Maracyn-Two, are effective in treating cotton wool disease. When used together, Maracyn and Maracyn-Two will also treat secondary infections. Oxytetracycline can be added to your pet’s food. Follow the directions on the package before using it. Also, you must remove any chemical filters from the tank before adding the antibiotics.

4. Raise the Salinity

Besides lowering the water temperature and adding antibiotics, you can also add aquarium salt to the tank. Increasing the water’s salinity will reduce your betta’s stress levels and strengthen its immune system. Follow the directions on the packaging to determine how much should be added. Normally, you should add one teaspoon of salt for every five gallons.

5. Partial Water Change

If you moved your fish from a community tank to a quarantine tank, I recommend doing a partial water change in the community tank. Every few days, change 25%of the water in the tank. Partial water changes should be part of your normal aquarium maintenance routine. By doing partial water changes, you will remove any remaining flavobacterium columnare.

While partial water changes should be done in the community tank, you should do complete water changes to the quarantine tank between medicative treatments. It’s very important to do so to avoid your betta from overdosing on the medication and prevent the water’s salinity level from getting too high.

How to Prevent Cotton Wool Disease

Preventing cotton wool disease is the same thing as providing quality care to your betta. Preventing cotton wool disease is also easier and less expensive than treating it. The following are ways to prevent this disease:

Avoid Overcrowding

One of the causes of cotton wool disease is poor water quality, meaning that the ammonia and nitrate levels are too high. These are created from fish waste and leftover food. The more fish you have in the tank, the more ammonia and nitrates will be produced. Because betta fish, especially males, can be aggressive toward other fish, I recommend keeping your betta fish by itself.

If you decide to keep your betta in a community tank, I highly recommend that you follow the general rule of one inch of fish per gallon of water. Remember that this is just a general guideline and to keep in mind that your fish may grow and exceed this limit quickly.

Water Maintenance

It’s also important to keep your aquarium clean and to remember that clear water does not necessarily mean clean water. The water can be clear but still have high levels of ammonia nitrates and flavobacterium columnare. You must test the water regularly to check for ammonia and nitrate levels. Ensure the aquarium has a good filtration system, and remove any uneaten food. Also, do a 25% water change weekly.

Quarantine New Arrivals

If you decide to keep a community tank, make sure you quarantine new arrivals for a minimum of two weeks and inspect the fish closely for any signs of illness. Don’t add the fish to the community tank until you are convinced that it’s a healthy fish.

Compatible Tank Mates

As mentioned before, one of the factors that cause cotton wool disease is stress. If your betta is kept in a community tank, ensure it gets along with its tank mates. Any fish that is being picked on will become stressed and a candidate for cotton wool disease.

Varied Diet

Feeding your betta a varied diet will help keep them healthy. Offer them frozen food, as live foods may contain harmful bacteria or parasites. Consider feeding:

 Please visit these pages for more information on betta care:

Your Betta Deserves Better!

We hope that you enjoyed this article. Bettas are sold in tiny bowls, leading to the belief that they do not need much room. Improper care is the cause of cotton wool disease, so providing the proper care can go a long way to preventing this disease. We invite you to leave your comments or questions.

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