Betta Fish Cotton Wool Disease: Causes, Symptoms, and Treatment

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By Linh Nguyen Updated on 02 Feb 2023

If you have a betta fish, then you may have heard of the term 'cotton wool disease'. Betta fish cotton wool disease is a bacterial infection that causes damage to the skin and fins of your betta fish. In severe cases, it can cause death. If you notice any of the following symptoms in your betta fish, it's important to take action and treat the infection as soon as possible. Symptoms include fin clumping, white patches on the skin or fins, redness around the wound site, swelling, and decreased activity. The Causes of Betta Fish Cotton Wool Disease are not fully understood but it is believed that stress factors such as changes in water temperature, pH levels, or water hardness may trigger the disease. luckily there are a few things you can do to help prevent your betta from getting infected and also treatments available.

In this blog post, we'll discuss the symptoms, causes, and treatment of Betta fish cotton wool disease. So read on to learn more!

A betta fish with cotton wool disease

A betta fish with cotton wool disease

1. What is cotton wool disease?

Cotton wool disease, also known as Flavobacterium columnare, is a bacteria that is commonly found in freshwater environments. This disease is highly contagious and is often fatal in bettas. Symptoms of the cotton wool disease include white cotton-like growths on the skin and fins, lethargy, loss of appetite, and increased mucus production.

This bacteria is spread through direct contact with contaminated water, and can also be transmitted through food or equipment that has come into contact with infected water. The cotton wool disease is an opportunistic disease, which means that it often attacks fish when they are already suffering from another disease that has weakened their immune system.

The cotton wool disease is a serious condition that can be fatal to betta fish. However, with prompt treatment, many fish can recover from this disease and go on to live healthy lives. Treatment focuses on preventing the spread of the infection and supporting the fish's immune system.

2. Causes

Bacterial infection is the most common cause of cotton wool disease in bettas. This type of infection is often caused by poor water quality, overcrowding, infection from new fish, or stress. Other possible causes include fungal infections, parasitic infections, and vitamin A deficiency.

2.1. Poor water quality

Poor water quality is the main cause of cotton wool disease, as it provides the perfect environment for bacteria to thrive. This is usually the result of inadequate filtration or not changing the water regularly.

Betta fish produce a lot of waste and if this waste is not removed from the water, it can quickly build up and contaminate the tank.

2.2. Overcrowding

As mentioned before, one of the main causes of cotton wool disease in betta fish is overcrowding. When there are too many fish in a small space, the water quality quickly deteriorates and becomes stagnant. This provides the perfect environment for bacteria and other pathogens to thrive. Moreover, betta fish are highly sensitive to poor water quality and can easily succumb to the disease.

Another problem with overcrowding is that it leads to insufficient oxygenation of the water. This is because the more fish there are in a tank, the more they produce waste. This waste then decomposes and consumes oxygen in the process.

Either way, keep your betta in a clean and well-ventilated tank to prevent this disease from developing.

A dirty fish tank

A dirty fish tank

2.3. Bacterial infections from new fish and new plants

Betta fish are very susceptible to cotton wool disease due to infection from new fish or new plants. This is because the betta's immune system is not as strong as other fish, and they can easily become infected with bacteria. When adding new fish or plants to the tank, it is important to quarantine them first to make sure they are not carrying any diseases. Otherwise, your betta could become sick and even die.

2.4. Stress

The cotton wool disease is often caused by stress in betta fish. Stress can be caused by a variety of things, including changes in water temperature, changes in water quality, and even aggression from other fish. When a betta fish is stressed, its immune system is weakened and it becomes more susceptible to diseases like a cotton wool disease. Therefore, it's important to try to keep your betta fish as stress-free as possible. This means providing them with a stable environment with consistent water parameters and not overcrowding their tank. If you do notice your betta fish showing signs of stress, such as hiding or reduced appetite, take action to correct the problem right away. By reducing stress in your betta fish, you can help prevent them from developing the cotton wool disease.

2.5. Fungal infections, parasitic infections

The cotton wool disease is caused by a number of different things, but the most common culprits are fungal infections and parasitic infections. Fungal infections can occur when bettas are kept in dirty water or water that is not properly filtered. Parasitic infections are usually caused by an infestation of microscopic parasites known as Columnaris bacteria. These bacteria can enter the fish's body through open wounds or through their gills. Once inside the fish, the bacteria multiply and release toxins that damage the fish's tissues and organs. This can cause the fish to develop ulcers, lesions, and eventually death.

2.6. Vitamin a deficiency

Cotton wool disease in bettas is most commonly caused by vitamin A deficiency. This can happen if the fish isn't getting enough of the vitamin in their diet, or if their body isn't able to absorb it properly. Deficiency can also occur if the fish is using up more vitamin A than usual, such as during periods of stress or illness.

Vitamin A is essential for bettas (and all other fish) in order to maintain healthy skin and fins. It helps to protect against infections and keeps the immune system functioning properly. A lack of vitamin A can make fish more susceptible to disease and stunt their growth.

3. Symptoms and pictures of betta fish cotton wool disease

Cotton wool disease, also known as columnaris, is a bacterial infection that affects the skin and fins of betta fish. The disease is most commonly seen in young fish but can affect fish of all ages. Symptoms of the cotton wool disease include white or gray patches on the skin, fraying of the fins, and ulcers on the body. This disease in bettas typically develops in two stages and is fatal if not treated early. Therefore, early detection and prompt treatment are very important. Below are the stages of development and symptoms of the disease.

3.1. The early stage

The early stage of cotton wool disease in bettas is characterized by the presence of small white spots on the body and fins. These spots are usually more visible on the fins than on the body, and they may be accompanied by a slight change in coloration. In some cases, bettas may also develop a mild case of fin rot. If left untreated, the disease will progress to a late stage.

During this stage, the betta will have some of the following typical behaviors:

  1. Fish have skin irritation and often rub against tank walls or hard objects to scratch.
  2. Betta fish may develop white patches on their fins and body.
  3. The betta fish's appetite may decrease, and they may become lethargic.
  4. The color of the fish is fading, less fresh, and in a pale appearance.
  5. The white patches may spread and the betta fish's fins may begin to fray.
a betta fish with early stage cotton wool disease

3.2. The late stage

In the late stages of betta fish cotton wool disease, the area around the fish's mouth becomes ruffled and sore-looking, resembling a cotton ball. This can often be mistaken for a true fungal infection, but if you look closely, you'll see that the fungal disease has long, hairlike fibers growing from it, while the mouth sore looks more like a crumpled-up cotton ball.

In addition to appearing around the mouth, this disease can also manifest as brown-yellow, white, or white-gray spots on the betta's head, fins, gills, or body. These spots usually have a red halo around them, and when they appear on the fish's back, they often look like a "saddleback" (a white haloed saddle on the back). 

Besides, the fins will also become increasingly damaged, and bettas may develop severe fin rot. The skin will become thin and frail, and the fish may stop eating. If left untreated, the cotton wool disease will eventually kill the betta.

At this stage, your betta will have a number of symptoms including:

  1. The fish's mouth appears ruffled and sore, like a cotton ball.
  2. The betta fish's fins and tail may rot away.
  3. The betta fish's body may become covered in ulcers.
  4. The betta fish may stop eating altogether and waste away.
  5. The betta fish may eventually die from the disease.

3.3. Distinguish cotton wool disease from other common diseases

The cotton wool disease is a fungal infection that affects the skin and fins of betta fish. The most common symptom is white, cotton-like growths on the body and fins. This disease is often confused with ich or body fungus, but there are some key differences that can help you identify it.

Look for white, cotton-like growths: The most distinguishing symptom of the cotton wool disease is the presence of white, fluffy growths on the betta's body and fins. These growths may look like cotton balls or pieces of lint, hence the name "cotton wool disease." If you see these growths, it's an indication that your fish has this disease.

Check for other symptoms: In addition to the white growths, bettas with the cotton wool disease may also exhibit other symptoms such as lethargy, loss of appetite, and difficulty swimming. If you notice any of these additional symptoms, it's likely that your fish has the cotton wool disease.

Compare to other diseases: As mentioned, the cotton wool disease is often confused with ich or body fungus. Ich is a parasitic infection that causes white spots on the body, while body fungus is a fungal infection that usually affects only the fins. Comparing the symptoms side by side can help you determine which disease your betta has.

If you suspect that your betta has the cotton wool disease, it's important to seek treatment right away. This disease is highly contagious and can quickly spread to other fish in the tank. Fortunately, there are a few different treatment options available that can effectively clear up the infection.

Here are detailed instructions for treating this disease.

4. Cotton wool disease betta treatment

The cotton wool disease can be treated with a number of different medications, including antibiotics, antifungals, and antiparasitics. The most effective treatment will vary depending on the severity of the disease.

4.1. Using aquarium salt

Mild cases of the cotton wool disease can often be treated with simple aquarium salt. To do this, follow the instructions below.

  1. Remove the betta from the tank and place it in a clean, disinfected container.
  2. Fill a small cup with clean, warm water. Add 1 teaspoon of aquarium salt and stir to dissolve.
  3. Using a cotton swab, gently apply the salt water to the affected areas of the betta's body. Avoid getting any in the betta's eyes or mouth.
  4. Allow the betta to soak in the salt water for 5-10 minutes.
  5. Rinse the betta off with clean, fresh water and return it to its tank.
  6. Repeat this process once or twice a day until the betta's condition improves.

The cotton wool disease is a common ailment in bettas, and can often be treated successfully with a simple salt water bath. If you think your betta may be suffering from cotton wool disease, follow the steps above to give them a soothing salt water bath. With regular treatment, most bettas will make a full recovery.

4.2. Using antibiotics

Use of antibiotics as treatment for the cotton wool disease in betta fish in the severe stage. The most commonly used antibiotics for this purpose are erythromycin and tetracycline. These antibiotics are effective against the bacteria that cause cotton wool disease, and they are relatively safe for use in betta fish.

The recommended dose of erythromycin for the treatment of cotton wool disease in betta fish is 10-20 mg/L. The recommended dose of tetracycline for the treatment of cotton wool disease in betta fish is 5-10 mg/L. These antibiotic doses should be given once daily for 5-7 days.

After the initial course of antibiotics has been completed, it is important to continue treatment with a broad-spectrum antibiotic such as erythromycin or tetracycline for an additional 2-4 weeks. This will help to prevent the recurrence of the cotton wool disease.

In some cases, it may be necessary to use a combination of antibiotics for the treatment of cotton wool disease in betta fish. If erythromycin and tetracycline are not effective, other antibiotics that can be used include ampicillin, cephalothin, and chloramphenicol.

The use of antibiotics is often successful in treating cotton wool disease in betta fish. However, you can remember that never be used for longer than the recommended course of treatment. Overuse of antibiotics can lead to resistance in the bacteria that cause cotton wool disease, and this can make the disease more difficult to treat in the future.

Treatment for Cotton Wool Disease in Fish

4.3. Other treatment

In addition to antibiotics, there are a few other treatments that can be used for cotton wool disease in betta fish. These include medicated baths and anti-fungal medications. Medicated baths using products such as Malachite Green or Formalin are often effective in treating cotton wool disease. Anti-fungal medications such as Ketoconazole or Clotrimazole can also be used to treat this disease.

4.4. Some important note

If you think that your betta fish may have the cotton wool disease, early diagnosis and treatment of this disease is the best way to ensure a full recovery.

Please refer to some of the following notes to make the treatment more effective.

  1. Sick fish should be isolated
  2. Change the water and clean the fish tank
  3. You can lower the temperature of the aquarium to slow the progression of the disease. The ideal temperature is around 75 to 78 degrees Fahrenheit - about 23 to 25 degrees Celsius.
  4. Keep a close eye on your betta during treatment and look for any improvements or deterioration in their condition.
  5. Be prepared to adjust your treatment plan accordingly if necessary. 
  6. Don't forget to consult your veterinarian if you have any concerns about your betta's health during treatment.

5. Is cotton fungus contagious?

While the cotton wool disease is not technically contagious, meaning it cannot be passed directly from one fish to another, it can spread quickly through an entire aquarium or pond if not treated properly. This is because the bacteria that cause the disease can live in filters, gravel, and plant material, as well as on the fish themselves. Once present in an aquarium or pond, the bacteria can infect any fish that comes into contact with it. For this reason, it is important to treat all fish in an aquarium or pond if one fish is diagnosed with the cotton wool disease.

Besides, some bettas may experience a relapse of the disease, while others may remain symptom-free. However, it is generally believed that bettas who have recovered from the cotton wool disease are more likely to experience another outbreak of the disease than those who have never had the disease before.

The most effective cure is to prevent it early, and cotton wool disease is a completely preventable disease.

Here are some tips to help you prevent this disease effectively.

Prevent cotton wool fungus

6. Prevent cotton wool fungus

The cotton wool disease is caused by a fungus that can grow on the skin and fins of betta fish. The fungus usually affects fish that are weak or sick, and it can be fatal if not treated quickly. There are several things you can do to prevent cotton wool disease in your betta fish: 

  1. Keep your betta's tank clean. A dirty tank is a perfect environment for the fungus to grow. Clean the tank regularly and remove any dead or decaying plants or animals.
  2. Don't overfeed your betta. A healthy diet is important for all animals, but it's especially important for bettas. Overfeeding can lead to problems with their digestion and make them more susceptible to illness.
  3. Make sure your betta has plenty of places to hide. A stressed fish is more likely to get sick, so give them plenty of hiding places in their tank. This can be anything from a cave to a piece of driftwood.
  4. Keep an eye on your betta's skin and fins. If you see any redness, swelling, or other changes, get tested and treated as soon as possible. The cotton wool disease can spread quickly, so it's important to catch it early.

By following these simple tips, you can help prevent cotton wool disease in your betta fish.


The cotton wool disease is a fungus that can affect betta fish. It is caused by poor water quality, and the symptoms include a white film or fuzz on the body of the fish. The disease can be treated with antibiotics, but it is important to take steps to prevent it from spreading. To keep your betta fish healthy and free from cotton wool disease, make sure you maintain good water quality and follow the tips we have shared in this article. Let me know in the comments if you have any questions about the cotton wool disease or how to treat it.

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