Fungus on betta fish: Causes, Symptoms and Treatment

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By Linh Nguyen Updated on 02 Feb 2023

Betta fish are one of the most popular fish kept in home aquariums, and while they are relatively hardy, they can still succumb to diseases. One such disease is caused by a fungus, which can lead to serious health problems for your betta. 

Fungus on betta fish is a common condition that can affect the health of your fish. There are many different types of fungi that can infect betta fish, but the most common type is Saprolegnia. Symptoms of fungus include white patches on the skin or fins, redness, swelling, and lethargy. This disease is treated with antibiotics, antifungals, or a combination.

In this post, we'll take a closer look at what fungus is, what causes it, and how to treat it. We'll also discuss ways to prevent fungus from occurring in the first place. So if you're concerned about this issue, keep reading!

A betta fish with fungus disease

A betta fish with fungus disease

1. What is fungus on betta fish?

Body fungus, also known as Saprolegnia, is a common condition that can affect betta fish. This condition is caused by a build-up of waste and debris on the body of the fish, which creates an ideal environment for the growth of fungi. Body fungus can lead to serious health problems for bettas, and even death if left untreated. Symptoms of body fungus include white or fuzzy patches on the skin, loss of appetite, and lethargy. If you notice any of these symptoms in your betta fish, you must treat it as soon as possible. Body fungus is relatively easy to treat, but it's important to catch it early before it causes serious health problems.

2. Causes

Mycosis, or more specifically Saprolegnia, is a type of fungal infection that can affect betta fish. The pathogen that causes mycosis is always present in the fish tank, but only attacks when the fish is weakened by a previous illness. This can be caused by dirty water, increased ammonia levels, or other stressors such as being bullied by other fish.

Some of the causes of your betta's weakness include:

  • Poor water quality
  • A dirty tank
  • Trauma to the fish (such as from fighting or being caught in a net)
  • A weakened immune system (from stress or disease)

3. Symptoms and pictures of betta fish fungal infection

Fungal infections in betta fish are often characterized by white or gray cotton-like tufts on the body, fins, or gills. Saprolegnia, as this condition is called, can be easily confused with mouth fungus (Columnaris) at a glance. However, upon closer inspection of the site of the fungal infection, one can see the presence of hair-like while the mouth fungus looks like a cotton ball.

In addition, ich (Ichthyophthirius multifiliis) – another common disease among bettas – can also be mistaken for a fungal infection due to the presence of white spots on the fish's body. However, these spots are actually cysts filled with parasites, not fungus. Thus, a careful examination of the affected area is necessary to make an accurate diagnosis.

Symptoms of a betta fish with a fungal infection may include lethargy, loss of appetite, and difficulty breathing. The fish may also display flicking or rubbing behaviors as it tries to rid itself of the fungus. In more severe cases, the fungus can spread throughout the body and cause death.

If you suspect your betta has a fungal infection, pinpoint the type of fungus that is infected and treat it as soon as possible to prevent the disease from spreading.

Here are some pictures so you can easily recognize this disease.

Close-up of a fungus on a betta

Close-up of a fungus on a betta

A betta fish infected with fungus - early stage

A betta fish infected with fungus - early stage

4. Betta fish fungus treatment

Fungal infections are a common ailment in betta fish. Many fungal infections are caused by poor water quality, so the first step in treating a fungal infection is to improve the water quality in your betta's tank. You can also isolate sick fish and treat a fungal infection with medication, either through topical application or by adding medication to the water. Be sure to follow the instructions on the medication carefully. Be very careful not to get the medicine on the gills as it can kill the fish

Some common medications used to treat fungal infections in betta fish include: 

  • Methylene blue
  • Pimafix
  • Tea tree oil
  • Acetic acid (vinegar)

Besides, you also need to note: aquarium salt and increasing the water temperature can help with fungus in bettas, but it is not a cure. You will need to continue to monitor your fish and treat them accordingly.

5. Is fungus contagious on betta fish?

There is some debate on whether body fungus, specifically Saprolegnia, is contagious among betta fish. Some experts say that the fungus can be passed from one fish to another, while others claim that it is not contagious. If you are concerned about your fish contracting body fungus, it is best to err on the side of caution and assume that it is indeed contagious. This means taking steps to isolate any fish that develop body fungus and keeping them separate from healthy fish. You should also clean and disinfect any tanks or other equipment that has come into contact with a fish with body fungus. By taking these precautions, you can help prevent the spread of this potentially deadly disease.

fungus fungus on betta fish in the heavy stage

6. Prevent fungus

Prevention is the best medicine when it comes to fungus. You can help prevent your betta fish from getting fungus by keeping their tank clean and stress-free. Make sure to do regular water changes and add a good filter to remove toxins from the water. Avoid overfeeding your fish and provide them with plenty of hiding places so they feel secure. If you suspect your fish has fungus, please isolate the sick fish and treat them as soon as possible.

To improve water quality and prevent fungal infections, be sure to:

  1. Regular water changes are important to maintain water quality and prevent fungal infections. 
  2. Avoid overfeeding your fish as uneaten food can decay and pollute the water. 
  3. Clean your tank regularly to remove any decaying matter that could cause water quality issues. 
  4. Consider using a filter to help keep the water clean and free of debris. 
  5. Make sure you are using clean, fresh water when doing water changes. 
  6. Quarantine new fish before adding them to your main tank to avoid introducing disease into your aquarium. 
  7. Don't overcrowd the tank - bettas need at least 2.5 gallons of water each
  8. Some strains of bacteria can help prevent fungal infections. Adding live plants to your tank can also help create a healthy environment for your fish.


While the fungus is not always deadly, it can cause major health problems for your betta fish and should be treated as soon as possible. In this post, we’ve outlined the causes, symptoms, and treatment of betta fish fungal infection. We also answered some common questions about fungus on bettas including whether or not it is contagious. If you suspect that your betta has a fungal infection, please don’t hesitate to reach out for help. Leave a comment below letting me know how you are preventing fungus from affecting your beloved pet fish!

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