Fin Rot

Fin rot is a common disease that occurs in fish of all types kept in an aquarium or pond. Also called tail rot, this disease destroys the tissue is the fins of the fish. If left untreated, the fish may lose the infected fin, and the infection may spread to other areas of the body.

As an aquarium or pond owner, you need to pay attention to the health of your fish and catch fin rot before it can become a severe epidemic and cause immense harm to your fish. Knowing the symptoms, causes, and treatment can help you to battle this disease successfully. Learning how to prevent it can keep your fish safe and healthy.


The cause of fin rot is a bacterium. There are different types that can lead to the disease, but they are all gram-negative. The bacteria cause damage by eating the membranes in the fish’s fins.

The bacteria are often helped along by the environment. This disease commonly occurs in tanks that have bad quality water. Cloudy or polluted water makes a spectacular place for the bacteria to breed and grow.

Another issue is aggressive fish. When one fish attacks another and tears the fins, this opens a direct route for the bacteria to cause an infection.

In the cases of bad water quality and aggressiveness, one of the biggest reasons for both is an overcrowding issue. Too many fish in an aquarium or pond will cause excessive waste and make fish uncomfortable, which can lead to aggression.


It is not too difficult to notice this disease. You should be able to see it easily once it is flourishing. You will notice the fins on your fish look rugged or torn. The fins may also have a black edging around them, which is a result of stress and damage. They may also have a loss of coloring. Your fish may also act differently. They may be sluggish and not eat normally.

Treating and Preventing Fin Rot

The first step you need to take is doing a complete cleaning of your aquarium or pond. You want to get rid of any bacteria existing in the water or components of your system. This means do an in-depth cleaning of every single part and area. If you cannot clean something, throw it out and buy new. This is not the time to take risks. You do not want to reintroduce the bacteria to your fish.

When putting your aquarium or pond back together, make sure to check the pH level. You also want to make sure the water you use is clean and pure so as not to introduce more bacteria into the situation.

Once you have your water ready, you can add in medication for treating fish rot. You can buy medicine specifically for fin rot. Melafix or Pimafix are the most common medications to find, yet they don’t have the strongest potency. Look around for medications at your local fish store that are specific to curing the disease. Do not worry about treating fish that are not ill. Adding the medication will not only treat the infected fish but also it helps to prevent a flare up in the future. So, all your fish will benefit from treatment.

To prevent an outbreak in the future, you should make sure to address the underlying issues. If lousy water quality was the main issue, then you should be more vigilant about maintaining it. Change the water frequently and use the proper additives to ensure the water stays in good condition.

If you noticed part of the problem was due to aggressive fish, then remove the aggressors. However, do not assume that just because you do not see the fish fighting all the time, that it isn’t happening at all. Sometimes fish will show aggression at night or behind rocks and coral. It only has to happen once for an outbreak to occur. You may want to keep an eye on your fish for a while to see if you can spot aggressive behavior.

The Bottom Line

Fish rot can be a terrible disease for your fish. It can lead to serious injury and death if left untreated. Not to mention that it makes your fish feel terrible. At the first signs of the disease, you should take measures to treat the fish and get rid of the problem. Then, make sure that you take steps to prevent it from occurring again. This will ensure your fish can live healthy and happy lives.