What is fin rot?

Fin rot is the term used to describe tissue deterioration on the fins of fish. It can cause large parts of the fins to detach, making it what is commonly known as ‘rotting away’.

If these symptoms are not recognised and treated quickly, fin rot will continue to spread throughout the body causing more fins to deteriorate until eventually death  occurs.  

It is important to act quickly if your fish are displaying any of these symptoms, but it is key that you identify the root of the problem correctly first before choosing the appropriate treatment for fin rot disease. There are two different types of fin rot; bacterial and parasitic . Let’s look at them in turn:

Bacterial Fin Rot

Bacterial fin rot is the most common form of fin rot disease. Usually, it is caused when a fish has been injured and inse cts enter the body through the wound. However if a fish’s natural defences are lowered for any reason, or they have a compromised immune system for whatever reason, an infection can become established in the fins and spread. This can be caused by a number of factors, such as poor water conditions or an underlying disease.

The symptoms of fin rot are usually easy to spot. The fins will become red at the base, before turning white in colour towards the tip. White cotton like ‘fungus’ may grow on the surface of the body of the fish, and this will spread if not treated. The fins will become ragged over time, often becoming so bad that large parts of the fin rot away altogether. Fish may display lethargy and stop eating, showing no interest in their surroundings.

Bacterial fin rot is most commonly caused by poor water quality or an underlying disease given time to spread.

If you notice any of these symptoms, it is extremely important that you take the time to identify the underlying cause before treating fin rot disease or moving onto treatment for parasitic fin rot . The best way to do this is to quarantine your fish and carry out a series of water tests (ammonia, nitrite and nitrate) in order to determine how much damage the bacteria has already done and if any internal damage has been caused. The best way to deal with fin rot is by treating the cause, not the symptoms.

If water conditions are not the reason for this disease, it is advisable that you visit a vet who can diagnosis your fish via an examination. Antibiotics can then be used to treat bacterial fin rot disease if the damage has been caused by bacteria.

Parasitic fin rot

The second form of fin rot, parasitic fin rot is much less common than bacterial fin rot. In fact, it occurs in only 2% of cases at most. This type of disease is caused when a parasite infects the fish , either via their skin or gills.

a) Skin flukes: These are flat worms that attach themselves to the fish’s skin, and cause damage as they suck out nutrients from their host.

b) Gill flukes: These are small flat worms that attach themselves to the gills of the fish and feed on blood. They can also damage tissue found on the gills if left untreated.

c) Leeches: These blood-sucking worms attach themselves to the fish via suction cups, and feed on their blood. They can also cause scars and lesions on the skin of the fish if left untreated.

Leeches are parasitic in nature and will attach to the host’s body

Fish infected with either gill or skin flukes may display loss of balance, sitting at the bottom of the tank or swimming near the surface. They may also be extremely lethargic, stop eating, and have damaged fins. Parasitic fin rot is most likely to occur when water conditions are poor, so it’s essential that you keep your aquarium clean and well maintained in order to prevent this disease from occurring.

How Do I Know If My Fish Has Fin Rot?

Fin rot can be hard to diagnose as the symptoms are very similar to those of other diseases, such as fin and tail biting. However, there are a number of simple tests you can perform to determine if your fish has this disease.

One way is to monitor your fish’s behaviour: healthy bettas do not go around nibbling on each other’s fins, so if you notice this behaviour it suggests fin rot may be responsible. Another simple test is to check the fins of your fish: healthy betta fins are transparent and their blood vessels should clearly visible within them. If they appear red, or there is white ‘fungus’ on the surface of them then it could be a sign of fin rot or another disease.

It’s also worth looking at the entire body of your fish: if it appears ragged and torn, with parts of its fins missing then this is a sure-fire way to tell whether you’re dealing with fin rot, or just bite marks from aggressive tank mates. Fish that have been severely bitten usually have deep, jagged tears in their fins. However, with fin rot these tears are smooth and even, appearing as though they have been cut with a blade or knife.

If you think your fish has fin rot it’s important to act quickly, as the disease can spread rapidly if left untreated.

How Do You Treat Fin Rot in Fish?

The best way to deal with fin rot is by making sure that you treat the cause, not the symptoms. This means water conditions should be thoroughly tested and adjusted if there are any issues. It’s also worth changing 10% of your tank’s water every week, as this helps keep water quality high.

Bettas need at least 2.5 gallons of water to live in comfortably, and under no circumstances should you overcrowd them. Not only does this make the fish more stressed, but it also increases their chance of contracting fin rot.

If you’re treated your betta for bacterial fin rot disease with medication make sure that the water chemistry is exactly right before adding the fish back into the tank. This is because medication may affect the levels of pH, hardness and ammonia in the water, so it’s essential it’s been carefully tested beforehand.

In terms of treating parasitic fin rot disease , all you can really do is monitor your fish and treat for any secondary infections that may occur as a result (such as fungal). If the fins seem healthy and the cause of infection has been removed then it’s likely that they will grow back.

Mild Fin Rot Treatment:

* Maintain good water quality, with a stable pH level of 6.5-7.5

* Allow the affected area to heal naturally

* If there are any secondary infections present, they may need to be treated with medicine that’s safe for betta fish

**NOTE: DO NOT apply any creams or ointments to the affected area

Anything that causes your betta to be stressed can increase the chances of it contracting fin rot, so the best way to prevent this from happening is by keeping them in a stress-free environment. This means maintaining good water quality and providing plenty of plants and hiding places so they have somewhere to retreat to if they feel threatened or scared.

It’s also important to remember that Bettas are labyrinth fish, so they need access to the surface of the water in order to breathe properly. For this reason it’s imperative their tank is tall enough: if there isn’t a gap between the top of the water and the lid then your betta could end up suffocating.

Moderate Fin Rot Treatment:

* Perform a partial water change, and remove the affected part of the fish’s fins

* Add aquarium salt to your tank (ensure it is suitable for bettas)

* Treat with an anti-bacterial medication that’s safe for Bettas

**NOTE: Only treat your betta if you know what caused it to develop fin rot

In some cases, it’s possible to save a betta that has contracted bacterial fin rot. This means you need to remove the affected part of their fins straight away, and keep them in a clean tank with suitable conditions until they have healed.

It’s important to remember that bettas can’t stay on the surface of the water for too long, so if their fins haven’t healed within a month they may need to be euthanized.

Severe Fin Rot Treatment:

* Perform a partial water change and remove the affected part of the fish’s fins

* Treat with an anti-bacterial medication that’s safe for Bettas

* Add aquarium salt to your tank (ensure it is suitable for bettas)

* Transfer your fish to a larger tank with more hiding places and plants

If you notice that the fin rot in your fish has become severe, it’s important to act quickly. This means removing the infected part of the fins and treating with anti-bacterial medication that’s safe for bettas. You should also add salt, and move your fish into a larger tank with more hiding places and plants.

If the fin rot is left untreated, it will spread throughout the entire body of the fish and they will eventually die.

How Do You Know If Fin Rot Is Cured?

* If the affected fins look healthy and begin to regrow

* The fish can be returned to its original tank once everything seems to have healed

* The other fish in the aquarium should also be treated for any secondary infections using safe medications

If you manage to treat your betta’s bacterial fin rot, it will take anywhere from two weeks to two months for the fins to grow back. You can tell it’s working by monitoring their progress, and assessing whether they look healthy or not.

If they start to look healthy again you can slowly return them to their original tank once you are sure that all traces of fin rot have disappeared. Make sure that their water is clean, warm and suitable for them, and keep an eye on your other fish too as they may end up contracting secondary infections.

As long as you are aware of the causes, symptoms and different ways to treat fin rot it shouldn’t be too difficult to take care of your betta fish. Provided you follow all the instructions given above, you should have no trouble keeping your fish happy, healthy and full of life.

Preventing Betta Fish Fin Rot

* Diet: a varied diet will ensure that your betta is receiving all the nutrients it needs to stay healthy, so try giving them live food as well as plant matter

* Temperature: Bettas prefer water between 77 and 86 degrees Fahrenheit (25-30 Celsius) so be sure their tank isn’t too cold or hot. You should also try to ensure that the water is filtered and well-oxygenated

* Water: Bettas are tropical fish so their tank needs a heater in order to keep the water at around 25 degrees Celsius. You should also keep in mind that bettas come from stagnant waters in the wild, so try not to add too many filters and aerators to their tank

If you’re thinking about adding a betta fish to your aquarium, it’s important that you know how to take care of them properly. The most important thing is providing the right environment so they can live happy and healthy lives. Betta fish are quite hardy so as long as you keep their water clean and warm, give them a good variety of food and give them the correct medication if they happen to contract an illness, you should have no trouble keeping your little friend as healthy as can be.


Betta fish are beautiful little creatures that can make wonderful pets, provided you know how to care for them. However, if they do fall ill you need to act quickly or else their illness could become severe and eventually kill them. Knowledge is power so make sure you know the causes of fin rot, what the symptoms are and how to treat it before it’s too late. Following all the instructions and precautions given here should ensure that your betta stays healthy and happy well into the future.

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