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Fin Rot is one of the most common and contagious diseases that can attack the fish in your aquarium. It is more common in slow-moving fish because their fins and tails are nibbled at by the fast-moving smaller fish species. Once these fins have been damaged, they are attacked by the bacteria inside the water that causes the infection. This infection leads to Fin Rot. You can treat your fish that have been infected with Fin Rot, but it has dire impacts on the health, quality of life, and lifespan of the fish inside your aquariums.

FIN ROT Dizzy Respect, CC BY-SA 4.0, via Wikimedia Commons

Fin Rot causes the fins and sometimes tails of the fish to rot, it rarely kills your fish if it is observed, and caught in the early stages. In advance stages of Fin Rot, however, it will be very difficult to cure the fish and they will die. Apart from this, Fin Rot is a highly contagious disease that can quickly spread from one fish to the entire aquarium. Hence, you need to quarantine the fish that has been infected and clean the water. Some preventive measures can be taken to prevent the spread of this disease and easily cure your fish. Below is a complete guide about curing the Fin Rot in aquarium fish.

What is Fin Rot?

Fin Rot is a fish disease that can cause the fins and sometimes tails of fish to rot. This happens because of the infection that is caused by several types of bacteria in the water. Another cause of this disease is stress. When your fish are under constant stress and are being attacked by aggressive fish in the aquariums, it can cause their fins to break. After that, multiple types of bacteria can attack the broken or injured fins. This causes the infection that starts to rot the fins of aquarium fish.

Another common cause of the Fin Rot in large and slow-moving aquarium fish is nibbling. When large fish are paired with smaller fish species, the smaller fast-moving fish nibble on the fins of large and slow-moving fish such as Goldfish. This nibbling causes the injury to find your fish, and those injured parts are infected by the bacteria. After that, the infection keeps spreading if not stopped and causes your fish to die. Also, these bacterias quickly replicate once they attack a fish. It allows them to latch onto other fish in the tank and infect the whole population of your tank. Once that happens, you will have to take all of your fish out of the aquarium, and treat them.

This can be a lethal disease if you are not cautious. You should keep looking for the signs of infection and Fin Rot. If you see any signs of Fin Rotting, you should separate that individual, change the water and maintain the parameters of your tank. This is one of the easy solutions that allow you to save your population in the early stages of the Fin Rot. But if the infection spreads and your whole tank is infected, you will have to use medications and go through a complete hygiene process.

Fin Rot is commonly seen in fish species with large fins and tails, but it is also seen in many other fish species. Below is a list of the types of fish in which this disease is common.

Species Commonly Affected By Fin Rot:

  • Betta Fish: Fin Rot is a very common problem in most of the betta fish species and varieties. Betta fish have large and beautiful fins and tails. These are mostly slow-moving species of fish. Fin Rot in this species happens when the fins are injured or infected by the environment, i.e. bacteria in the water. This causes the fins of the betta fish to rot and degrade. It not only destroys the beauty of their fins and tails but also causes the fish to die in some cases. But, it is a preventable and curable disease in betta fish. You can stop the rotting but these fins may not recover 100%.
  • Goldfish: Fin Rot is also common among the goldfish varieties. This is also because their fins are very long. These long fins and tails can be bitten by the members of their tank or get injured because of fights or accidents. It causes infection and swelling at first and after that, these fins start to rot. This is also a preventable and treatable situation if caught in the early stages. You should treat your goldfish for Fin Rot using medicines and take preventive measures to stop it from attacking your fish once again.
  • Guppies: Guppies are also a group of fish in which the Fin Rot disease is common. This species also has large fins that can get bitten, or injured for various reasons. These injured parts attract the bacteria and this causes the infection and rotting of the fins and tails. You can prevent this from happening by maintaining the parameters in perfect ranges. It is also a curable disease but requires time and treatment using medicines.
  • Rainbowfish: Rainbowfish is also a popular aquarium fish that is prone to Fin Rot. In this fish species, Fin Rotting can happen after injuries or after being bitten during fights. Once the bacterias start attacking the fins and tails of the fish, you will notice that the tail and fin have started to degrade. The situation will become worse as time passes. So, you need to make sure that you catch this disease on time and cure it.

Apart from these fish species and groups, this disease is commonly seen in various other types of aquarium fish as well. As mentioned above, it is treatable and preventable but you need to be careful and maintain proper hygiene, and parameters. 

What are the causes of Fin Rot?

This disease is mostly caused by a group of bacteria that attacks the broken or injured fins of the fish. But it can also be caused by the several other issues that are discussed below in detail. The types of bacteria that cause this disease include Pseudomonas fluorescens, Aeromonas, and Vibrio. These bacteria and several types of fungi that are present in water attack the fins of your fish in aquariums. The growth of these bacteria and injuries to the fins are the main problem or causes of concern. Because they only grow or attack the fish if they are present in the water. Below is the list of common causes of Fin Rot in aquarium fish.

  • Bacterial and Fungal Infections: There are several types of Fin Rot causing bacterias and fungi that can attack your fish in aquariums. Most of these bacteria are transferred to healthy and clean tanks when you start using one tank supplies into other tanks without properly disinfecting, washing, or cleaning them. It is almost impossible to know if these bacterias and fungi are present in your tank or not. But you can prevent them from growing in your aquarium by maintaining proper hygiene. Keeping your tank clean will prevent their growth and replication and will allow you to keep your fish in the tank without worrying about Fin Rot.
  • Nibbling, and Injuries: Bacterias and Fungi need an entry point to attack the fins. This entry point is provided to them when the fins of the fish are nibbled or injured because of some reason. These injured fins are prone to infections caused by the presence of bacteria in your tank. So, you need to make sure that you prevent injuries in your tank. Also, you should not pair slow-moving fish with fast-moving and hyperactive fish because the fast fish nibble on the fins of small fish and cause injury. Making them more prone to infection and Fin Rot.
  • Poor Quality of Water: Poor quality of water is one of the main reasons behind the spread of this disease in aquarium fish. A lot of fish keepers fail to maintain the proper quality of water in their tanks. This allows the growth of Fin Rot causing bacteria and fungi in your tanks. If you maintain the proper quality of water, you will not have to worry about the Fin Rot in your aquarium fish.
  • Stress, Fighting in Tank: Stress is another cause of the fin and tail rot in many fish. Stress is usually caused by a hostile environment and tank conditions. For example, if the water quality in your tank is not good, or if there are predators or very aggressive fish species present in your tank. It would cause stress on peaceful fish species. Also, pairing peaceful species with aggressive fish would make the peaceful fish more prone to being attacked. These attacks cause physical injuries and emotional stress in the fish that can lead to extensive fin and tail rot in many fish species.
  • Irregular Water Temperature: Irregular water temperature is a perfect condition for the growth of most of the bacteria and fungi in your tank. Also, it causes stress on your fish as the change in water temperature directly impacts the health of your fish. So, if you fail to maintain a constant temperature in your tank within the recommended range, the chances of occurrence of Fin Rot in your tank will increase. For that reason, you need to know the recommended water temperature range and make sure to maintain the temperature of your tank within that recommended range.
  • Overcrowding In Aquarium: Overcrowding in aquariums is also one of the main problems that cause the fin and tail rot of aquarium fish. If you have a small tank, you should only put a small number of fish. It is better to follow the fish per gallon ratio to know the number of fish that you can keep in an aquarium and do not exceed that limit. Overcrowding of the tank causes territorial issues and fights. Which is an ideal situation for the stress and Fin Rot to occur.
  • The improper pH level of Water: pH level of the water helps you maintain the overall chemistry of the water in your tank. The improper maintenance of the pH can cause several issues. For example, if the water is too acidic, the scales of fish will burn because of that and that will cause the Fin Rot to occur. Similarly, if the alkalinity of your tank is high, the fish would also be more prone to bacterial or fungal Fin Rot. You need to maintain the pH of the water in your aquarium within the given range to prevent this from happening.

What are the symptoms of Fin Rot?

The symptoms of Fin Rot will help you know if your fish has Fin Rot or not. These symptoms depend on the stage of the disease. For example, in the early stages, the symptoms are mild and you can hardly tell if your fish is infected or not. But as the disease progresses, the symptoms become more obvious. In this disease, time is everything. If you can detect the problem early and can prevent it from spreading, you can save your entire tank. Below are some details about the symptoms of Fin Rot.

●     Physical Symptoms:

At first, you can detect the disease from the physical symptoms. These symptoms include fin damage or thinning of the fins of your aquarium fish. You will notice that the fins have started to become colorless, and dull. You will also notice physical injuries if those are the reasons for Fin Rot in your fish. You will notice that your aquarium fish fins have started to become frayed. This is the start of this disease and if you have caught the signs of Fin Rot at this stage it will be easy for you to treat it.

If you were unable to notice the frayed fins, the next physical symptoms will be more obvious. You will notice that the fins have started to degrade and fall apart. At this stage, you will also notice that the base of the fins of your aquarium fish has become swollen. This can be because of infection or injury or both. At this stage, treatment becomes hard and you may have to quarantine your fish before treating it to prevent an outbreak in your tank.

Make sure to thoroughly check each individual of your tank so that you can successfully identify all of the infected fish and healthy fish. The third indicator of the Fin Rot in aquarium fish is the change of color of the entire fin. It only happens to the fins that have been infected and that are about to fall. It is the last stage of this disease where the chances of fins falling apart are much greater. Also, at this stage, the disease would spread to your entire tank, and treatment of the Fin Rot would not produce any positive results.

You should keep looking for these physical indicators or symptoms of the Fin Rot in your aquarium fish. To do this, you may need to observe your fish closely. In large fish species, it is easy to spot this problem early on. But in smaller species, it becomes difficult to identify the disease using physical symptoms, unless you take the fish out of the tank and inspect its fins. A lot of expert fish keepers advise physical inspection of your fish over time. This is done to catch the disease in the early stages and treat it.

Apart from these physical symptoms, you will also notice some behavioral changes in your fish because of the Fin Rot. These behavioral symptoms can also help you identify if the fish has been infected or not. You will notice that your fish is swimming in distress mode, it will change its swimming pattern, and in some cases, you may also see the extreme signs of stress in your aquarium fish. If any of these behavioral changes are found in your fish, you should take them out and inspect them carefully to look for the physical symptoms.

How To Treat Fin Rot?

As mentioned above, Fin Rot is a serious health concern for many aquarium fish species. You need to treat your fish to make sure that they become healthy once again. Otherwise, the chances are that your aquarium fish will die. To treat the Fin Rot in different fish species, you need to follow a plan.

Stepwise Treatment Plan:

Below is a stepwise treatment plan for the Fin Rot that you should follow to make sure that you cure infected and diseased fish and prevent the disease from ever coming back.

1.   Cleaning Your Tank:

The first step is cleaning your entire tank. As you know, this disease spreads because of the unhygienic living conditions, and incorrect parameters, you need to start with the cleaning. Take out all the water in your tank, put your fish in another tank for a while. Make sure that the other tank has everything right. After that, clean everything that was inside the tank, wash it, disinfect it, put it out in the sunlight for a day or two. After that, you can refill the tank using filtered water. This time, make sure that the parameters such as temperature, pH, and hardness are within the given ranges. This will help you treat your fish if the disease is in its initial stages. You may not even have to use any medicine at this stage.

2.   Quarantine Infected Fish:

But if the disease has progressed and bacteria have infected the fins, it will be better for you to evacuate and quarantine the infected fish. Create a hospital tank for your infected fish species, and put them in that tank to treat them. This will help you prevent an outbreak of Fin Rot in your original tank. Once the fish have been treated in the hospital tank or quarantine, you can put them back in the original tank.

3.   Treating Fin Rot Using Antifungal Medicine:

In some cases, fungal medicine works. But this is only necessary for Fin Rot when Fin Rot in your aquarium fish is occurring because of the fungal problems in your tank. Fungal spores are everywhere they travel through the air, found in water and all they need to grow and infect is a host. They latch on to the scales and fins of the fish and infect the fish. This causes swelling and falling of the fins and tails in many fish species. In that case, you will have to use antifungal medicine for the treatment of Fin Rot.

4.   Treating Fin Rot Using Antibiotics:

You can also use antibiotics to treat your aquarium fish of Fin Rot. Antibiotics are commonly used in fish aquariums to treat health issues caused by bacteria. The antibiotics kill the bacteria that were infecting your fish and it will help you cure the rotting fins quickly. Also, it will help you prevent another outbreak of the Fin Rot in your tank if you can disinfect the entire tank using antibiotics. But you should not use them by yourself, ask a veterinarian to help you in this matter.

5.   Treating Fin Rot Using Aquarium Salt:

A lot of expert fishkeepers also use aquarium salt as a treatment for Fin Rot. Aquarium salts kill bacteria, maintain salinity, pH, and hardness. This allows you to create perfect living conditions for your fish, meanwhile, these conditions discourage the growth of bacterial and fungal diseases including Fin Rot.

How To Prevent Fin Rot In Your Aquarium?

Once you have treated your fish with medicine or using any of the steps that are given above, you will need to make sure that the Fin Rot never comes back to your aquarium again. You can do this by taking preventive steps. Below are some of the preventive steps that can help you prevent Fin Rot in your aquarium fish.

  • Change Water and Filter:

You should start with changing the entire water in your tank and start using a new and better filter. The presence of diseases in your tank is an indicator that your filter is not working properly. So, you should use a better filter for your aquarium. Also, changing the water of your tank will eliminate the bacteria that were present in the previous water. Make sure to use clean water for your aquarium that has been tested for use.

  • Correct the pH in Your Tank:

The next step is to know the correct pH of your tank and change it according to the needs of your fish. If the fish likes to live in an acidic environment, maintain an acidic pH level, but if your fish needs alkaline habitat, maintain the pH levels in the alkaline range. Most fish species like to live in neutral environments. It is important to know the optimal pH levels for your fish and maintain them in the tank throughout the lifespan of the fish.

  • Maintain Water Temperature:

Temperature is also one of the very important factors that you need to maintain properly. Some fish species like to live at room temperatures, while some live below or above room temperature. Make sure that you know the exact range of temperature in which your fish can live and try to maintain it throughout the years.

  • Isolate Fin Nibbling Fish:

The fin nibbling fish species can be a real problem, you must isolate them or keep them in a separate tank. Try to learn about selecting suitable tank mates for your fish. This would allow you to know if a fish can be kept together with other fish or not. Putting a fin nibbling fish with a slow-moving fish can lead to fin injuries, and Fin Rot and that is why they should be kept in a separate tank.

These are a few measures that you need to take to make sure that Fin Rot never returns to your tank. Despite taking these preventive measures, there is still a chance that Fin Rot might occur in your tank. So, keep checking the physical and behavioral symptoms in your fish. This would allow you to quickly identify the disease and treat it accordingly.


Fin Rot is one of the most commonly occurring diseases in aquarium fish. If you are not careful, there is a chance that your fish will get this disease. For that reason, it is better to take preventive measures, maintain the pH, hygiene, temperature, and hardness of the water. Also, it is important to use clean and filtered water for your aquariums. Also, if the Fin Rot attacks your aquarium fish, you can treat it using specific treatment methods that include cleaning the tank, quarantining the fish, treating using antifungal, antibacterial medicines, and aquarium salt. You can use any or all of these measures to treat your fish. It is better to ask for help from a fish expert or an aquarium veterinarian.


Question: Is Fin Rot contagious?

Answer: Yes, Fin Rot is a contagious disease. This is spread by bacteria that are present in unhygienic tanks and that can quickly spread from one fish to the entire tank.

Question: Can Fin Rot kill your fish?

Answer: Yes, in severe cases of Fin Rot, the infection can lead to the death of your aquarium fish. That is why it is important to identify this disease and treat your fish.

Question: What is the best Fin Rot treatment?

Answer: According to expert fish keepers, preventive measures are the best treatment, but if the disease attacks your fish, you should use antibacterial, antifungal medicines, and aquarium salt. All of these treatments work as long as you maintain the tank parameters and hygiene.

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