What Causes Fin Rot In Bettas (Symptoms & Treatment Guide)

You love your betta fish and want to keep it healthy for as long as possible. Unfortunately, betta fin rot is a common problem that can make your pet fish feel uncomfortable and unhappy. You may not even notice the symptoms of fin rot at first, but treating it quickly is the best way to avoid severe fin rot developing. So what causes fin rot in betta fish?

Betta Fin Rot is caused by a bacterial infection, often triggered by poor water quality or a lot of stress. The result of fin rot is decaying fins and tissue that lead to your betta fish losing its beautiful colors. White milky fin edges are a good indication of a fin rot infection.

Common Names: Fin rot, fin melt, body rot, mouth rot, and gill rot.

Scientific name: The bacterial form is known as Pseudomonas fluorescent.

Betta Fin Rot Symptoms: Uneven, ragged, and stringy fin tips that are pale, yellowing, or dark brown in appearance. Maybe signs of mucus covering the infection area. Fungal Infection will look more white and fluffy, eating away at the fins more evenly.

Cause Of Betta Fin Rot: Lowered immunity and poor water conditions cause your betta fish to become more susceptible to a number of “gram-negative” bacteria such as Aeromonas, Pseudomonas fluorescens, or Vibrio. Fungal fin rot is often more likely to appear on injured tissue.

Fin Rot Treatment: Antibiotics for jagged fins (bacterial infection), or a suitable antifungal for fin rot that is more even. Aquarium salt can ease discomfort and promote recovery. There are many suitable commercial treatments available such as malachite green, phenoxyethanol, or methylene blue.

Outlook: Unless severe infection has taken hold, causing severe fin and body tissue damage, treatment is often successful and most fish make a full recovery.

Betta Fin Rot Symptoms And Treatments

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If you want to learn about betta fin rot in more detail, the rest of this article talks further about the causes of betta fish fin rot, how to spot the symptoms, and how you should treat the condition if it does show up!

If you are new to betta fish, I also have an article called Setting Up A Betta Tank (The Right Way!), which is well worth a read.

Also, make sure to check out our Betta Fish Care Guide And Species Overview.

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What Causes Fin Rot In Bettas
What Does Betta Fin Rot Look Like

If your betta fish has fin rot, it is very easy to miss the condition unless you know what you are looking for. The most obvious signs are:

  • Your betta’s fin tips will become pale, milky white, dark brown, or yellowish instead of their usual vibrant colors. After your betta has had fin rot, the tips can appear transparent as they begin to grow back.
  • Parts of the fin rotting away and falling off (this can happen within a few days!).
  • The fins become stringy or frayed with jagged fin edges.
  • You may also notice that your betta fish has a mucus-like film on its body, indicating fin rot.

When the fin rot infection is fungal, the fin edges will be less stringy and frayed, and instead will rot away more evenly, appearing more white and fluffy.

When suffering from severe fin rot, betta fish have quite a hard time and will probably stop eating and sleeping which will make them grumpy. A male betta’s fins are large and flowing, so when fin rot sets in, the fragile membrane can become heavily affected, often ending up with a large amount of fin loss.

Fin loss suffered by your betta fish will eventually grow back, however, the quicker you can spot the onset of fin rot symptoms, the quicker you can treat it. If caught really quickly, your betta may only have minor fin loss around the edges.

The video below will give you many examples of what betta fin rot looks like.

Betta Fin Rot Symptoms, Treatments, and Prevention

If you don’t treat your betta fish right away when it has fin rot, this condition will worsen. The decaying tissue starts to spread all across the fins and infect other areas of your betta fish’s body.

There are many different treatments available to treat fin rot in bettas. I will discuss some of these treatments a little later on.

What Causes Fin Rot In Bettas

Betta fin rot is a common bacterial disease. Dependent on where the infection is found, it may be referred to as tail rot, gill rot, mouth rot, or body rot.

There are many ways betta fish can contract fin rot, but it’s important to understand the most common causes, so you know how to prevent them!

The main cause of betta fish fin rot is poor water quality. If your tank isn’t properly cycled or maintained and ammonia, nitrate, and nitrite levels aren’t checked every week, your betta fish will be more susceptible to bacterial infections.

Bacterial fin rot can be caused by many types of bacteria classed as “gram-negative”, such as Aeromonas, Pseudomonas fluorescens, or Vibrio, which eat the soft, delicate membranes around the fins.

A Fungal infection will often develop at the infection site, appear white and fluffy, and can be referred to as fungal fin rot. Fungal fin rot is most easily noticed when your betta fish fins are turning white at the edges.

If you have a sick betta fish, fin rot can set in much quicker because the immune system is already compromised. There are many parasites and bacteria often present in a betta tank just waiting to strike when a betta’s immunity is down, and this is the best time for fin rot is most likely to happen.


Mycobacteriosis is a more serious bacteria that can evade the most common fin rot treatments. If the treatments you have tried do not seem to clear the infection, your fish will probably have this type of bacteria.

If any of these bacterial infections are left untreated, the fish will usually die.

Several causes can lead to bacterial fin rot, such as:

  • Stress causes a betta’s immune system to be down. A lowered immune system can also be caused by other less obvious problems.
  • Poor water quality.
  • Injuries from betta fish fighting and fin nipping with other fish or other betta fish in the aquarium.
  • Parasites (eustrongyloides) can cause fungal infection (fungal fin rot).
  • Keeping the aquarium heater at the wrong temperature.

Is Betta Fin Rot Contagious

Bacterial fin rot on betta fish is very contagious. If your betta has bacterial fin rot, the whole tank will already be saturated with the harmful bacteria that cause it. Keeping fish apart will not stop the fin rot from spreading to other fish, instead, you will need to treat the entire tank.

Although fin rot is contagious, your betta will still need a lowered immunity for the bacteria to take hold. As I mentioned previously, the harmful bacteria that can cause fin rot on betta fish are common, and often go unnoticed with no ill effects.

Betta Fin Rot Symptoms

Apart from looking at your betta’s fins, there are several other symptoms you can look out for like:

  • Lethargy
  • Betta not eating (loss of appetite)
  • Dark brown or gray patches on the fins and body. These patches are usually found on the edges where they meet other fins. Fungal fin rot can appear lighter and more fluffy or cotton-like.
  • Rubbing the body up against objects in the tank, or even other fish to try and get relief.
  • Finding your betta hanging at the top of his aquarium without being able to swim downwards. This is because he feels like he has no energy left to move around!

Some of the symptoms above are also common in diseases like betta white spot, better known as ich/ick.

If you haven’t treated the fin rot early enough, rotting patches will eventually start to spread across other parts of the body.

Betta Fin Rot VS Fin Loss

It is sometimes hard to distinguish between fin rot and fin loss caused by other tank mates nipping at your betta’s fins.

Betta fish can be aggressive toward other fish, often meeting their match, and becoming injured themselves. A betta’s fins are also delicate and they can attract a lot of attention from other fish.

In my early years of fishkeeping, I added a betta fish to my own community tank. The betta seemed a little timid, and I guessed it was because of the new environment. The following day I looked In my fish tank, but couldn’t see my betta anymore.

After 20 minutes of looking, I noticed a strange, finless creature wobbling around the tank. IT WAS MY BETTA!! which soon died.

Not understanding why this had happened, I tried one more betta and discovered that both my Angelfish and my Gouramis were fin-nipping my betta until all of its gorgeous plumage was gone.

This is a drastic case of fin nipping, and it will often happen on a much smaller scale. As betta fish have such long wavy fins, they are an easy target for most fish to nip at, and this will cause many recurring infections.

The damage caused by fin nipping will often progress to fin rot as the damaged fins are more susceptible to bacteria and parasitic infection.

Fin Rot Or Nipping

It is usually quite easy to distinguish between fin rot and nipping.

The most common signs of nipping are:

  • The fin edges will appear clean-cut if caused by damage from other fish. Fin rot would appear as tattered and frayed fin edges.
  • Ripped fins or split fins can be caused by fighting, or damage can be caused by sharp objects in the tank during fighting.
  • If you have recently added a new fish to the aquarium, then it is highly likely that they are responsible for nipping at your betta’s fins.
  • A timid betta hiding out in the fish tank. might be having its fins nipped.
Fin Nipping In Betta Fish
Fin Nipping And Fighting In Betta Fish Is Very Common.

As I mentioned earlier, damage caused by nipping can be the trigger for betta fin rot to set in, so it is important to quickly move the perpetrator to a separate tank or a separate container if you only have one tank.

If your betta fish’s fins begin to rot, it is quite easy to distinguish from nipping because the mushy dark appearance will usually stand out quite well in comparison to the usual bright colors.

Betta Mouth Rot

Betta mouth rot is a bacterial or fungal infection also referred to as mouth fungus, cottonmouth, or cotton wool disease because it appears like mold or a white wooly fungus. Betta mouth rot is caused by Flexibacter Columnaris or Flavobacterium Columnare bacteria.

Early Stage Betta Mouth Rot

In the early stages, your betta’s mouth rot may cause a loss of appetite due to the discomfort caused inside its mouth. At this stage, you may notice some small strings of a white, cotton-like substance protruding from your betta’s mouth.

As mouth rot progresses, you will certainly notice a white substance coming out of your betta’s mouth and mouth rot can quickly spread to the gills where it will affect breathing.

Treatment for betta mouth rot is the same as for fin rot which I will describe in more detail below. However, because it is a bacterial infection, a simple over-the-counter anti-bacterial medicine should be quite effective in most cases.

During a case of mouth rot, it would be worth changing your betta’s diet to something more manageable other than pellets. The best food for betta fish will be something soft and easy to eat. Your betta won’t want to chase live food around the tank when they have mouth rot, so frozen or freeze-dried foods like baby brine shrimp, or bloodworms will help.

How To Treat Fin Rot Betta

One key factor in how to treat betta fin rot successfully is to recognize it in the early stages. Betta fin rot can be caught at many stages, and you will often be treating fin rot differently at each stage. Early-stage fin rot will cause less initial damage and be easier to treat.

Always check water parameters and water temperature first.

Treating Mild Fin Rot On Betta Fish

Mild fin rot is when caught at its earliest stage. Only the fin edges are usually affected and may look a little soft and melted.

Mild fin rot treatment is usually more simple. Just add aquarium salt to the aquarium water. You can buy aquarium salts at most pet shops, and you just need to follow the guidelines on the label.

Medication may or may not be necessary. If you don’t feel the infection is clearing or don’t want to take the chance of it spreading, use one of the medications listed below for moderate fin rot.

If you are in the stages of mild fin rot, you should definitely check the water quality in your aquarium and ensure the proper temperature is set and maintained.

Poor water quality is a main contributing factor to fin rot and can be caused by uneaten food debris, poor filtration, and a general lack of cleaning.

All of these factors will eventually lead to a build-up of bad bacteria, which can cause fin rot.

It is important to carry out regular water changes and use a gravel vacuum to remove any debris from the substrate. Regular water changes will keep bacteria levels down, and the result should be healthy fish.

Treating Moderate Fin Rot In Betta Fish

Moderate fin rot will need immediate attention, especially if your betta has an aggressive personality.

If you have caught the fin rot at this stage and immediately move the infected fish to a quarantine tank, it will be easier for treatment.

As already mentioned above, aquarium salt can help heal mild or moderate betta fin rot, but it is not always easy to ensure all of the water in your fish tank is covered with aquarium salt.

By using betta fin rot medication, you can treat any type of betta fin rot easily and effectively without adding salt.

Three medications that are effective against betta fin rot are:

BettaFix For Fin Rot by Aquarium Pharmaceuticals

API Bettafix For Fin Rot

MelaFix For Fin Rot (Malachite Green) 16 Fluid Ounce Bottle

API Melafix For Fin Rot

Fritz Aquatics Mardel – Maracyn 2 Antibiotic Treatment

Mardel - Maracyn 2 Antibiotic Treatment For Fin Rot

These medications can cure mild to moderate betta fin rot in only one day, however, you need to change 50% of your fish tank water before adding this product, and it can be harmful to any live plants or invertebrates.

All of the medications I have mentioned are highly recommended. They will act fast and only need minimal changes to your tank conditions.

There are many more medicines available, and you should always check whether they are treating bacterial, fungal, or parasitic infections (or all 3).

Moderate betta fin rot treatment can also involve adding aquarium salt daily until the infection clears up. This will not cure the fin rot infection, but it will help to soothe the discomfort and reduce stress.

Treating Severe Fin Rot In Betta Fish

Fin rot treatment is easier if caught early. Severe fin rot treatment is more time-consuming, will take longer to act, and is often far less effective. Advanced fin rot can cause a fast decline in the health of your betta fish, and it may die.

Ideally, move your betta to a quarantine tank as soon as possible. The quarantine tank will stop other fish from contracting fin rot so easily.

Change your aquarium water every day and add betta fin rot medication twice daily for up to five days.

You should notice a difference after only one day of treatment. Still, you must complete the full dosage until all signs of infection have gone away completely before stopping the medication.

The use of betta fin rot medicine means you don’t need to change your aquarium water so drastically.

If the betta is still eating, it will tolerate a small amount of medication in its tank. If your betta stops eating, this would be a problem and potentially be a sign that your betta is dying.

In this case, remove all medications from the tank immediately and do a 50-60% water change to lower the medication levels.

It is important not to over-medicate your betta and always follow the manufacturer’s dosage advice exactly.

Although betta fin rot treatment should be easy, you need to ensure that any medications used will not harm other fish or plants in your aquarium, as this could lead to secondary infections, which are harder to treat.

Can Fin Rot Heal On Its Own

It is possible that fin rot can heal on its own. A betta will usually become more susceptible to the infection if the immune system is down. Should the betta’s immune system improve, it may fight the infection without medication.

Personally, I wouldn’t rely on this happening and would always want to treat an infection as early as possible as bacteria and parasites can spread quickly through the aquarium water.

If you have a community tank, other fish risk contracting fin rot.

How Long Does Fin Rot Take To Heal

How long fin rot takes to heal is difficult to answer. The infection itself can be treated and cleared relatively quickly, although the physical scars need to heal.

Betta fish will experience fin regrowth over time (usually several months), and the fish’s body will heal quite quickly. Providing there is no major fin damage, you will need to wait patiently and nurse your betta fish back to health.

How To Tell If Fin Rot Is Getting Better

You can tell if fin rot is getting better by your betta fish’s general mood, and the fins should appear less mushy.

It does take time to notice any real physical signs, as there needs to be some fin regrowth first, so it is easier sometimes to make sure the condition is not getting any worse.

As long as the fin damage has stopped, you can be assured that the fin rot has been cured.

As fins begin to grow back they will have a transparent appearance and they will be very fragile at this stage of re-growth.

Betta Fish Fin Re-Growth
Betta Fish Fin Re-Growth Can Be Seen As A fragile Transparent Edge.

How To Prevent Betta Fin Rot

The best way to treat betta fish fin rot is through prevention, so let’s find out how to prevent betta fin rot and ensure you take all the necessary steps.

To prevent fin rot, it is advisable not to overcrowd your aquarium and keep the water clean at all times, checking water parameters regularly. I have a great post on How Often To Change Betta Water – What you need to know.

This will also reduce stress levels in your betta fish which could cause their immune system to be compromised as they fight off infections or parasites.

Also, you need to ensure you are not overfeeding your betta. Feed only what they can eat in two minutes and remove any uneaten food after this time as it will pollute the water and increase nitrate levels which could lead to fin rot developing.

Betta fish living in a clean tank with plenty of space will boost their immune system. They will not feel overcrowded and will be much less likely to contract fin rot.

The steps to prevent betta fin rot are pretty simple, but too many fish owners will ignore the basics and end up having to treat fin rot instead, with potentially devastating consequences.

Wrap Up

Betta fin rot is a preventable disease that’s caused by too much stress on the fish. If your betta has an open sore or wound, it will be prone to infection and could get worse if not treated right away.

If you notice any of these symptoms in your pet, make sure to take them to the vet for treatment as soon as possible. It’s best to avoid this problem altogether with simple steps like keeping your tank clean, so bacteria don’t grow there and being mindful about how you feed them food – they’ll be less stressed when eating well!

Frequently Asked Questions

Wikipedia – Fin Rot
University Of Florida –Use Of Antibiotics In Fish
The Aquarium Wiki – Fin Rot

Jon O'Connell

I have kept both marine and freshwater fish and set up almost 100 aquariums. Although I am no longer doing it professionally, I hope I can help others to enjoy keeping happy, healthy fish by sharing my many years of experience.

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