Mouth Rot: What is It ? And How to Treat Mouth Rot in Fish

What is Aquarium Fish Mouth Fungus?

How to Treat Mouth Rot in Fish

Even though it is called “mouth fungus,” it is actually a bacterial infection that needs to be treated with antibiotics or other medicines that kill bacteria. Most of the time, mouth fungus is found in the head, but not always in the mouth. It could also affect the face, gills, and jaws. It can also affect the body and fins less often, so it’s easy to mistake it for fin rot. But the short tufts that show up when someone has a mouth fungus are unique. True fungal infections are similar to mouth fungus infections, but fungal infections usually look like tufts of long, white, fluffy threads, while mouth fungus infections usually look off-white to grey. Some aquarists call mouth fungus “cotton wool disease,” which is confusing because true fungal infections don’t look like cotton.

Mouth fungus that has gotten worse can also cause sores and lesions on the head and along the sides of the body.

Cause And Triggering Factors

Like the bacteria that cause finrot, the bacteria that cause mouth fungus are found in all aquariums and usually don’t cause any harm. In fact, they help the biological filtration process by turning organic matter (like fish poop) into inorganic chemicals that the biological filter bacteria can use. But just like finrot bacteria, mouth fungus bacteria will feed on living cells and tissue fluid if they get the chance.

When fish get hurt, like when they fight or bite each other’s fins, their skin breaks and bacteria gets in. Usually, the fish’s immune system will kill any invading bacteria, preventing disease. However, if the fish’s immune system is weakened by stress, a bad diet, or, most commonly, a bad environment, the invading bacteria can take hold in the wound. So, when mouth fungus shows up, the aquarist should make sure that the fish aren’t fighting or biting each other, that they are all kept in the right social groups, that their diet is balanced and full of vitamins, and that the water quality is good. Mouth fungus is strongly linked to levels of ammonia and nitrite that are higher than zero, but water chemistry and oxygen levels may also be to blame.

When compared to finrot, mouth fungus tends to spread slowly. However, some strains of mouth fungus spread much faster than the normal kind and can kill infected fish in just a few days. So, a quick diagnosis and treatment are very important.

Mouth fungus is a disease that affects fish. It is caused by bacteria that attack the fish’s mouth and make a cottony growth that makes it hard for the fish to breathe and eats away at its jaws. Mouth fungus can be treated with antibiotics and other medicines that can be bought in stores.


Mouth fungus should be easy to treat with antibiotics that work against gram-negative bacteria, like kanamycin. Antibacterial medicines like phenoxyethanol (100 mg/l for 7 days) and nifurpirinol (0.2 mg/l for up to 5 days, also called furanace or nitrofurazone) have also been used successfully. Note that some of these medicines, like nifurpirinol, can hurt the bacteria that live in the filter.

Because it can be hard to tell the difference between mouth fungus and real fungal infections and bacterial finrot, many of the medicines made specifically to treat mouth fungus also treat fungus and finrot. Long-term success is, of course, tied to how well the fish are cared for, so it is likely that a review of water quality, water chemistry, diet, and social behavior will be needed.

Salt and oil from tea trees

Tea tree oil from Melaleuca trees has been used to keep fish from getting bacterial infections. This has worked to some degree. If a fish has been hurt or cut, separating it from the source of the problem and then treating it with tea-tree oil may help prevent mouth fungus, finrot, and real fungal infections.

Salt (sodium chloride) isn’t very good at treating mouth fungus, but at a dose of up to 1 oz per US gallon, it may help prevent bacterial infections in general. But keep in mind that the amount of salt needed to prevent bacterial infections will be too high for most freshwater fish. Salt is only useful for fish that can handle salt, like guppies and mollies.


The first medicine I tried was Paraguard from SeaChem. I already had it at home. It is said to work against bacterial, fungal, and parasitic diseases in fish. a medicine that can be used to treat many different kinds of problems in fish. SeaChem says that it should be used on all new fish in a quarantine tank, even if there isn’t a problem. They say it’s not too harsh and won’t hurt the fish or the biological filtration. a great medicines for the first time.

Even though ParaGuard was used for more than a week, the mouth rot did not go away. A few of the neon rainbowfish started to have bad mouths. On the plus side, it didn’t affect the biological filtration because I tested the water often with the API Freshwater Master Kit.

I went to the official SeaChem forum and asked what product I should use to treat fish mouth rot. They told me that Paraguard should fix the problem most of the time, but that some strains of bacteria may be resistant to some medicines. In this case, I had to take stronger medicines . They then said that KanaPlex was a good choice.


KanaPlex was something I bought. It was an antibiotic that worked in a wide range of ways. It is also thought to be able to treat bacterial and fungal diseases in fish. Both mouth rot and fin rot were listed in the product description as diseases that could be treated. It was also said that fish could easily take in water through their skin and gills. So, you don’t have to eat or drink anything. But the SeaChem staff told me that KanaPlex would work better if I soaked the fish food in it first.

I did what they told me to do and put the pills in water, but I also soaked all of the dry food in water first. I put high-quality New Life Spectrum pellets that had been soaked in VitaChem and Garlic Guard on top of the KanaPlex.

I must just have bad luck. The mouth rot was still there after more than the recommended six days of treatment. There was no sign of getting better.

On the other hand, the fish were much healthier after I took care of them. When they first got there, the rainbowfish were all dull colors. They were also shy and quiet at first. During the first few days, they threw up most of the food and didn’t eat the rest. After only a few weeks at my house, they were much brighter and more active. At each meal, they actively chased after the food. Even more, the men started to court the women all the time.

One day, I was surprised to see some free-swimming fry in the fish tank. They were so little, and they didn’t look anything like their parents. I guess I should have expected it, since there was a female and three males in the quarantine tank, as well as a big piece of java moss that would be a great place to lay eggs. Oh, and the dwarf neon rainbowfish couldn’t have been born without the Java moss.

I moved the four adult dwarf neon rainbowfish to a 5-gallon tank because of this. so that diseases don’t get passed to the fry. Adults did not eat the fries, though. They got no attention at all. One time, I saw an adult rainbow fish swallow a fry by accident. He immediately spat it out. They must have more brains than most fish.

Let’s get back to what really matters.

I went back to the forum for SeaChem. The staff was unhappy with what I did. KanaPlex should have done what it said it would do. They thought it might be because the strain was immune to KanaPlex. They said that the next one to try should be sulfathiazole.


Sulfathiazole is another antibiotic and antifungal medicines. It claims to be very good at treating infections caused by bacteria. The description said that both fish mouth rot and fin rot can be treated. I ordered it online because of this.

Since I moved the four infected rainbowfish to the 5-gallon tank, I needed less of the medicine in the water to reach the right level.

Even after just a few days of treatment, the lips looked better. Within a week, none of the symptoms could be seen anymore. Just to be sure, I kept going with the treatment for two more weeks. Most likely, there was no need to keep the treatment going for that long.

Last changed: December 9, 2017 A new product from SeaChem called SulfaPlex is now on the market. The only thing in it is sulfathiazole. The name of their item was changed. The medicine is called SulfaPlex, and the antibiotic is called sulfathiazole.

Effect After Treatment

In my case, sulfathiazole worked where other medicies had failed. It doesn’t mean that other medicines won’t work for some cases of mouth rot. My fish had a strain of Columnaris that could not be killed by ParaGuard or KanaPlex. It could still be killed by sulfathiazole. There is a chance that different fish owners will have different experiences.

The good news is that neither the disease nor the medicine hurt the fish (there were over 50 of them). All of them grew up well. When they were about the size of my thumbnail, I gave more than 30 small Neon Rainbowfish to friends. The rest are living happily ever after in an aquarium near me.


Mouth fungus doesn’t usually show up in aquariums that are well-kept. Instead, it’s more common in aquariums that have serious management and/or stocking problems. So the best way to keep mouth fungus from happening is to make sure your aquarium is set up, stocked, and cared for properly. This means that the aquarium needs to be properly cycled before fish are added. It also means that the fish need to be carefully chosen so that they have the same needs in terms of water chemistry and temperature, and that their social behavior is also properly managed. Fish can easily hurt themselves by fighting, which can lead to mouth fungus. This is especially true for cichlid fish, which like to use their jaws to “wrestle.” Mouth fungus is easy to get in your aquarium if you keep livebearers in soft, acidic water or tropical fish like bettas in an aquarium that isn’t heated. Most of the time, goldfish get sick in aquariums that don’t have filters or that have too many fish in them.

Medications Food

It’s easy to make food that can heal. In the microwave, heat 1/4 cup of water, which is two ounces or 58 milliliters, which is not a lot. Then, stir the hot water while adding 1/4 ounce of plain gelatin (one envelope of Knox gelatin), pectin, or agar. Take two tablespoons of dry commercial fish food (pellets or flakes) and mix them with just a little of the hot water and gelatin mixture. Add hot water and gelatin until the mixture looks like paste. Just add more food if it gets too watery.

Then, add just a “smidgen” (about 1/16 of a teaspoon, or 1% to 2%) of the medicine to the mud. If you are taking more than one medicine, mix them together and only take a small amount of the mixture. If you’re using a packet of medicine, only take a “smidgen” of what’s in the packet. Mix and mash the mass well. On a piece of plastic wrap or a plate, spread it out into a pancake about 1/8 inch (3 mm) thick. Then put them in the fridge. Put it in a small plastic bag and freeze it if you want to keep it for more than two weeks.

All of the fish in the tank should be fed the antibiotic-laced food every day for at least ten days. Keep in mind that it doesn’t really matter how much medicine is in the food. Antibiotics are only dangerous in large amounts over a long period of time, so it’s pretty easy to take too many of them. Antibiotics in the food don’t hurt the filters, so you can leave them in place and use them.

If you can’t help but treat the water, take out the sponges and/or foam from the filters and put them in an open container for the time it takes to treat the water. Antibiotics sometimes kill the good bacteria and sometimes don’t. In any case, the antibiotics will be destroyed by the filter media. If the ammonia level goes above 1 ppm, you would change 50% of the water. 2/3 of the food should be taken away.

Keep in mind that if you don’t have any antibiotics, it’s easy to take a pill or capsule of an antibiotic meant for people and use it on fish. If it’s a pill, you can just crush it. Just remember that antibiotics for humans are about ten times stronger than antibiotics for aquariums, so a “smidgen” in the food is more than enough. This is a great choice for people in Europe or Canada, where antibiotics in fish are against the law.

If fish in an aquarium have a bacterial disease, the whole aquarium needs to be treated. This is an important matter. Don’t waste your time with herbs, tree-leaf oils, or other treatments that don’t work. Ben Ochart used Pimafix and Melafix to treat an infection caused by bacteria. Nothing was done to stop the disease. Before he used antibiotics to stop the infection, he lost a lot of big, beautiful fish.


Is Mouth Fungus in Fish Contagious?

Fungus is not contagious, so sick fish can be treated in a quarantine tank away from other animals.

What Causes Fungus in Fish?

Fungal infections are often caused by water that is not clean enough. We see a lot of this disease in betta fish because they are usually kept in small containers without a heater or filter.

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