What is the mouth rot in betta fish?

In this article, we will answer the question “What is the mouth rot in betta fish?”. We will also discuss some symptoms and how to treat mouth rot in betta fish.

What is the mouth rot in betta fish?

Cottonmouth condition, also known as a cotton wool disorder, fish mouth rot, or oral fungi, is a common fish illness in home aquariums that affects cottonmouths and cotton wool. It’s so common that it happened to me during my first year of aquarium fish ownership.

Why do fish get mouth rot or mouth fungus condition?

Because it resembles mould or a cotton patch, most people call it mouth fungus. Specifically, it is caused by the bacteria Flexibacter columnaris or Flavobacterium columnaris.

Bacteria can be found practically anywhere, including in aquarium water. At a well-managed tank, these potentially harmful bacteria are present in extremely low concentrations. They eat organic debris like fish excrement and fish food that has been leftover from previous meals. Fish that are in good health have an immune system that is capable of beating off even low amounts of harmful bacteria. 

If the bacteria in a tank are not correctly maintained, the tank will become overrun with bacteria. They can also be opportunistic and broaden their food source to include the live tissues of the fish. 

Fish don’t have hands, therefore they use their mouths to touch, consume, and battle. Their mouths are the most commonly injured area. Bacteria have an easier time getting a foothold in an open wound. The fish’s mouth may appear to be coated with white lipstick for a brief length of time if this happens to it. If the situation worsens, the fish lips will be covered by what seems to be white or greyish mould or cotton. The fish lips might be observed decaying or falling apart in more severe cases. 

Columnaris can infect the gills and fins of the fish. Gill rot and fin rot/fungus are terms used to describe these conditions. The rot that has developed in the jaws of fish will not disappear on its own. The fish will perish if nothing is done to save it. Rainbowfish and other catfish species are especially vulnerable to sickness. In spite of the fact that it is infectious, even if ill fish are brought to the same tank, healthy fish in well-managed tanks may not be affected. 

If a fish habitat has poor housing conditions, such as too many fish, poor water quality, low-quality fish food, or a high level of stress, the illness will most probably spread to the whole aquarium if the problem is not addressed immediately and effectively.

What is the best way to cure Columnaris in betta fish?

If you catch columnaris early enough, your betta can recover completely. Follow the instructions outlined below to offer your betta the best possible chance of healing and long and healthy life. 

1. You must move your betta into a quarantine tank. Here is where you will find all you need to know about quarantine tanks, including instructions on how to put them up. 

2. Make certain that your quarantine tank contains nothing that your betta can ingest and become ill. You’ll also want to use conditioned tap water to fill the tank. 

3. Drop the temperature to 75°F while dealing with columnaris, despite the fact that a betta’s ideal temperature is 78°F in most cases. Columnaris flourishes at warmer temperatures, thus temperatures below 75°F will make it difficult for the bacteria to survive and grow. 

4. Now that your tank’s temperature is correct, you should start treating your betta with an antibiotic. Furan 2 is an excellent choice, and you should use it according to the instructions on the bottle or consult a professional. 

5. In addition to Furan 2, aquarium salt should be used. This will aid in the reduction of his stress and the strengthening of his immune system. Before applying aquarium salt, make sure to check the directions again, although 1 teaspoon every 5 gallons should suffice.

6. Remember to do a thorough water change before redosing if you’re using Furan 2 and Aquarium Salt, otherwise, you run the danger of inflicting more injury to your betta fish. 

7. Additionally, you should perform 25 per cent water changes in your main tank every 3 or 4 days, on top of treating your betta. This will help in the eradication of any columnaris that may still be present in your tank.

If you follow these measures and catch columnaris early enough, you should see an improvement in your betta after a few days. If your betta’s condition appears to be deteriorating, you’ll need to switch to a stronger antibiotic, such as Kanamycin. 

You can also try mixing Kanaplex with Furan 2, but be aware that this can impair your tank’s biological filter, necessitating more water changes.

How can I keep Columnaris from infecting my betta fish? 

According to the old proverb, “An ounce of prevention is worth a pound of treatment”. The best method to deal with a columnaris outbreak in your tank is to prevent it from happening in the first place. Here are a few strategies to keep your betta and tank free of columnaris infections. 

• Check to see that your tank isn’t overloaded – An packed aquarium is one of the most prevalent causes of columnaris. When this happens, trash and germs will accumulate faster than you and your filter can remove them. According to basic guidelines, you should have one gallon of water for every inch of fish in your tank. However, larger fish will require more room.

• Clean your tank regularly — When the water in your tank appears to be fine, cleaning it feels like a hassle. If the water looks to be perfectly clear, it may nonetheless be teeming with hazardous germs despite its apparent purity. You should frequently suction the sediment and eliminate any algae that have grown in your tank. Fish excrement that sinks to the bottom of the tank provides the ideal environment for bacteria to thrive. 

• Replace the water regularly – You should replace the water in your tank on a regular basis, regardless of its size. The smaller the aquarium, the more water you’ll have to replace, and the more frequently you’ll have to change it, so plan accordingly.

• Quarantine any new fish – Before introducing any new fish to your tank, it is recommended that you isolate them for a period of time to ensure that they are in good health. This way, you’ll be more likely to find out whether they’re contaminated while also reducing the risk of bacteria spreading to your main tank. 

• Disinfect previously used equipment – If you’ve already used any apparatus to cure sick fish, make sure it’s completely disinfected before you use it again. Your tank will be entirely saturated with bacteria after just one reintroduction. 

• Check for aggressive behaviour in your fish — If your betta is hostile toward other fish, or other fish are aggressive toward your betta, remove the offender as quickly as possible. All other fish’s immune systems will be weakened by aggressive fish. If your betta has a weakened immune system, it will be more susceptible to columnaris infection.

• Provide a well-balanced diet for your betta — Bettas require a lot of meat in their diet. They can get malnourished if they don’t eat enough meat. And if they’re underweight, they’re more susceptible to contract columnaris, as well as a variety of other illnesses.

What are the benefits of having a quarantine tank?

To avoid the growth of fish mouth rot from the beginning, an isolation aquarium is necessary to be set up. Due to the fact that the quarantine tank is far smaller than the main tank, the medicine dosage can be reduced as well. 

If you have a new fish or two who have mouth fungus, you may simply treat them with KanaPlex or SulfaPlex to get rid of the problem. Before beginning the medication, detach the carbon plate from your filter and discard it. The propensity of activated carbon to absorb drugs from water renders the treatment useless. 

Please remember that Columnaris bacteria like hot water, which should be around 80 and 90 degrees Fahrenheit at all times. Keeping the water temperature between 70 and 75 degrees Fahrenheit during an outbreak can help to prevent mouth rot. The vast majority of tropical fish should be alright at this temperature provided the water temperature is progressively reduced by no more than 3 degrees Fahrenheit every hour, the slower the reduction the better. The immune systems of tropical fish will be compromised if the water temperature is too chilly for them to survive. Therefore, you should avoid doing so as well.


In this article, we answered the question “What is the mouth rot in betta fish?”. We will also discuss some symptoms and how to treat mouth rot in betta fish.

If you have any questions or concerns, please let us know in the comments section below!

Frequently Asked Questions (FAQs): What is the mouth rot in betta fish?

Is fish mouth rot contagious? 

The bacteria are found everywhere in freshwater, but cultured fish raised in ponds or raceways are the main source of infection. It’s frequently misdiagnosed as a fungal infection. The sickness is exceedingly contagious, and it frequently leads to death.

What causes mouth rot in a fish? 

Mouth fungus is a fish bacterial disease that attack the fish’s mouth, generating a woolly cottonlike development that interrupts respiration and erodes at the fish’s lips. Mouth fungus is a contagious disorder that affects both freshwater and marine fish. When it comes to treating oral fungus, antibiotics and other commercially accessible medications can be employed.

What does the fungus in a fish’s mouth look like? 

Some people mistakenly believe that the fish has a fungal illness because of the look of white or greyish-white patches on its head. However, a fungal infection normally begins as a pale zone around the fish’s head and mouth. This may acquire a yellowish-brownish colour with reddish borders.

Why does the mouth of my fish remain open? 

The fundamental reason a tropical fish appears to breathe a lot is that there isn’t enough oxygen in the water, so they have to suck oxygen into their mouths rather than take it in through their gills. Despite the fact that this is an extreme case of a lack of oxygen in the water, the concept is the same.

Do fish lips regrow? 

Ciliary fish, like humans, can heal the immediate injury region, resulting in scar tissue. Unlike bony fish, cartilaginous fish cannot regenerate a new fin if one is lost. 

What is a good method for increasing the amount of oxygen in fish water?

Water flow typically results in an increase in oxygenation, which is beneficial. If additional filters are required, they should be added or the existing filters should be replaced with ones that have a larger capacity. Some more options include the use of a powerhead, the connection of a spray bar to the filter’s output, or the use of airstones.


How to Treat Mouth Rot in Fish. 2022. https://www.bettafishfacts.org/mouth-rot-in-fish/

Columnaris In Bettas (Cotton Wool Disease Cure). https://www.bettacarefishguide.com/columnaris-in-bettas-cotton-wool-disease-cure/

Cotton Wool Disease In Betta Fish: Treatments. https://bettasource.com/cotton-wool-disease/