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Fin Rot in Aquarium Fish: Causes & Treatments (With Pictures)

Sarah Psaradelis

By Sarah Psaradelis

fin rot

We all want to see our beloved fish happy and healthy in their aquarium. If you peer into the aquarium to admire your fish, only to find out your fish has ragged fins, you may be dealing with a case of fin rot.

Many different diseases can still affect healthy fish even if they are kept in ideal conditions. One of the main concerns in both tropical and cold-water freshwater fish is fin rot. It is heartbreaking to see your fish battle this infection, and it not only affects their appearance but their quality of life too.

Diagnosing and treating fin rot in the early stages will prevent it from developing into a severe case. Fin rot is not often fatal if it is treated early, but it can become deadly very quickly. This article will tell you everything you need to know about this common infection.

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Quick Fin Rot Fact Sheet

Severity: Mild to moderate
Common names: Fin melt, fin rot, & tail rot
Caused by: A secondary infection to open fin wounds, improper water conditions, & fin nipping
Most susceptible fish: Mostly goldfish and betta fish
Bacterium strain: Pseudomonas flourescens or (P. flourescens)
Affects: All freshwater fish
Treatment: A good-quality medication and water changes

What Is Fin Rot & How Is It Caused?

To put it simply, fin rot is an infection mainly caused by bacteria in the water that eats away at the fins of most freshwater fish. It may appear as if the fish is eating chunks from its fins. This can make them appear raggedy and shredded. It is not a disease itself, but rather classified as a symptom of another disease and should be referred to as an infection.

The bacteria or fungus begin to rot away large chunks of the fins starting from the end and it makes its way to the base of the fish if left untreated. This then causes the fish to lose its ability to swim properly, which affects eating, oxygen intake and prevents them from doing simple tasks.

betta fish in aquarium
Image Credit; ivabalk, Pixabay


Fin rot is mainly caused by poor water conditions or secondary infection (bacteria or fungus) because of fin nipping, either by the fish itself or another fish in the tank. When combined, the case can become severe. If your fish has been nipping its tank mates’ fins or even it is own and the water contains the bacteria Pseudomonas flourescens, this bacterium enters the wounds of the fish and causes rapid physical deterioration from the secondary infection. It is more common in small aquariums that have inadequate filtration and too many fish. This increases the tank’s bio-load and causes an overall unhealthy environment for them.

External factors like first-degree fungal and bacterial infections are a common cause of mild to moderate cases of fin rot. Water quality plays a major role in the development of the infection.

Which Species of Fish Are More Likely to Develop Fin Rot?

sick betta fish
Image Credit: Wirestock Creators, Shutterstock

Fin rot is most common in goldfish and betta fish; however, many species of fish can be affected by this disease.

Bettas are the number one species of aquarium fish that is likely to develop fin rot in their lifetime. This is because bettas nip and chew at their fins out of stress, boredom, or annoyance.

You see, male bettas have long, flowing fins that make them poor swimmers. When they feel like their tail length is an annoyance factor to their poor swimming ability, they begin to chew and shred their tail. The open wounds on the tail make it easy for the bacteria to enter and cause an infection. Bettas can also get their fins torn by a sharp decoration.

Goldfish can develop this infection from poor water conditions which harbor a variety of pathogens that can lead to infections. Goldfish produce a large amount of waste which makes the water quality deteriorate rapidly. These bacteria or fungi then eat away at the fins, resulting in fin rot.

Fin rot can affect most species of tropical fish, commonly Plecostomus, gourami, cichlids, tetras, mollies, and live-bearing fish.

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Types of Fin Rot


Pseudomonas flourescens bacteria is the number one cause of bacterial fin rot in aquarium fish. It is commonly found in aquariums lacking general maintenance and hygiene. In terms of water changes, filter cleaning, or even overstocked aquariums where the fish’s waste builds up too quickly.


This is less common but can be identified by a white edge on the shredded parts of the fins. However, it should not be confused with healing which appears as a thin white membrane on the ends of the fins.

Secondary infections

An open wound on a newly torn or nipped fin allows pathogens to enter the wound. These bacteria can be naturally found in aquarium water, but only affect the fish if they have an external injury. Secondary infections can only occur from a previous disease or wound.


Symptoms of Fin Rot in Fish

  • Loss of appetite
  • Ragged fins
  • White film on the end of fins
  • Weight loss
  • Visible spine
  • Dull coloration
  • Chunks missing from the fins
  • Lethargy
  • Clamped fins
  • Difficulty swimming

How Long Does Fin Rot Take to Heal?

Fin rot takes about 2 to 6 weeks to fully heal depending on the severity of the infection. Fin rot can only heal if proper treatments are administrated, along with clean aquarium water and lots of time to heal without stressors being present in their environment.

Sometimes the fin rot may be too severe, and the only option is to humanely euthanize the fish to end their suffering. If your fish has extremely damaged fins with little to none left to keep them afloat in the water, your fish may lay on its side or float around the tank. This is a good indication that the infection is too far along for a successful recovery.

If you suspect your fish is sick and want to ensure you provide the right treatment, we recommend that you check out our best-selling and comprehensive book The Truth About Goldfish on Amazon today.

The Truth About Goldfish New Edition

It has entire chapters dedicated to in-depth diagnoses, treatment options, a treatment index, and a list of everything in our fishkeeping medicine cabinet, natural and commercial (and more!)

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The 5 Steps to Treat Fin Rot

1. Move Fish

Move the infected fish to a hospital or recovery tank. It does not have to be very big. This makes it easier to treat the fish without worrying about the medication affecting the main tank’s fish or live plants. Some medications can even destroy a cycled tank by killing off the good bacteria. So, you want to find an unused 5- or 10-gallon for this step.

2. Place Air Stone

Place an air stone into the hospital tank so that your fish does not have to worry about swimming up for oxygen. This only adds unnecessary effort that your sick fish is already struggling with. If it is a tropical fish, a heater should be placed inside as well.

A blue aquarium air stone held in the palm of someones hand
Image Credit: Tanakon Phoophaphiw, Shutterstock

3. Treat with Medication

Treat with a medication that applies to the type of fin rot your fish has. (See recommended products below)

4. Follow Through

Finish the recommended dosage on the medications label and use this medication for 1 to 2 weeks.

5. Water Change

Do a large water change in the main tank before placing the sick fish back inside. This prevents the healing fins to become infected again.

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How to Treat Fin Rot in Goldfish

Treating fin rot in goldfish is slightly different than it would be to treat other fish species affected by fin rot. Since goldfish mainly get fin rot from poor water conditions from the high amount of waste produced, keeping the water clean is the most important step. You should do a 50%-70% water change and add in 1 tsp of salt per every 5 gallons of water. You can also do medications dips, where you place the goldfish in a bucket of concentrated fin rot medication for 10 to 30 minutes, and then place them back in the main tank to fully heal. Do this for a week until you notice that the fins are healing.

Image Credit: zh y, Pixabay

Best Medications to Treat Fin Rot

These medications can be used in the main tank while your fish is still healing from fin rot:

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Fortunately, fin rot is treatable for every species of fish. It is a mild to moderate infection in aquarium fish, and it is very common. If you notice that your fish is showing signs of fin rot, it is important to treat this infection right away. The sooner you treat your infected fish, the higher the mortality rate will be.

We hope that this article has helped inform you on everything you need to know about fin rot, and how you can diagnose and treat your fish for a successful recovery.

Featured Image Credit: Wirestock Creators, Shutterstock

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