Fin Rot in Goldfish (Causes, Symptoms, Treatment, & Prevention)

To see fin rot in goldfish is a sad thing. These fish are so beautiful and, well, worth their weight in gold. They are so beautiful to look at and bring us relaxation and joy as we watch them swim around their tanks or ponds.  

In this article, you’ll learn how to recognize fin rot and how to treat it so your goldfish remain as healthy as possible for years to come. So, keep reading!

Key Takeaways:

  • Fin rot in goldfish is a common disease marked by the fraying or rotting of a fish’s fin or tail.
  • Recognizing fin rot involves observing signs such as rotted or fallen-off fins, inflammation at the fin’s base, and white, brown, or black edges.
  • Stress is a significant factor causing fin rot, triggered by factors like overcrowded and unclean tanks, aggressive tank mates, or changes in the environment.
  • Fin rot is caused by bacteria, including Pseudomonas, Aeromonas, and Vibrio, often exacerbated by poor water quality.
  • Symptoms of fin rot include discolored fins, shorter fins, development of fungal infections, and white dots on the fins.

What Is Fin Rot in Goldfish?  

Fin rot in goldfish is a very common disease that marks the fraying or rotting of a fish’s fin or tail. To recognize this, look closely at the fins and tail.  

Do you notice any of the following? 

  • Part of the tail/fin has rotted away or fallen off 
  • Inflammation at base of the fin 
  • Tail edges or fin edges are white, brown or black 
  • Frayed edges are present around the fins/tail 

Your fish will also experience a loss of appetite, lessened activity, and sit around at the bottom of the tank. 

What Causes Fin Rot in Goldfish?  

Here, we will talk about why fin rot happens and where it comes from. It is one of the most common afflictions you will face as you own aquarium fish, but rest assured, it is very preventable.  

Fin rot may be caused by many bacterial species, but the reason your fish get it is due to an environmental reason- stress being the most factor in fish that are affected by such a disease.  

For example, stressors in fish include being moved around, a tank that is overcrowded and unclean, or tank mates that are aggressive in nature.  

SubtopicKey Information
Bacterial CausesPseudomonas, Aeromonas, and Vibrio bacteria.
Environmental FactorsStress from overcrowded tanks, unclean conditions, aggression.
Transmission of Fin RotInfected fish nipping healthy tankmates, spreading the disease.
Role of Water QualityPoor water quality as a significant contributor.

Caused by Bacteria

Fin rot is caused by the pseudomonas, Aeromonas, or vibrio bacterias. It is easy to prevent but difficult to fix once it has set in, especially as the disease advances. If you do not treat the fin rot, it will kill the fish affected by the disease and could very well infect the other fish living in the tank. 

The infected fishes nip at the tail and fins of the healthy tankmates, which ends up spreading the disease thanks to this physical contact.  

Let’s look a bit closer at these bacteria: 


It is a common bacteria you will find across the globe. It is present in plants, soil, and water.  


It is a gram-negative bacteria and leads to many diseases in goldfish and koi. It is also the reason behind goldfish ulcer disease and may occur in freshwater fish and marine fish. Hemorrhages are found on gills, muscles, fins, and tail, as well as internal organs. Quarantine is necessary to help your fish recover from this ailment. 


The illness that comes from this bacteria is known as Vibriosis. When it comes to aquarium fish, this can result in hemorrhages and skin ulcerations, ulcerations of the fins, skin, and tail, as well as the degeneration of the internal organs. 

More often than not, poor water quality will be the culprit behind your fish contracting fin rot. Other times, the cause will be because fish got stressed out due to moving or being handled. If water temps are too low or too high, it can cause the fish to feel stressed out. We will discuss these factors below:  

More on Poor Water Quality 

If you’re feeding your fish outdated food, overcrowding the tank, or failing to provide the fish with adequate filtration or clean the tank regularly, you are putting your fish at risk of getting sick. Spikes in ammonia or nitrite can happen, which are bad for the fish in your tank.  

Making sure you are regularly cleaning the tank and replacing the filters will be your best bet. You also have to make sure you are keeping the appropriate number of fish for your tank size.  

Lastly, make sure you are feeding only what your fish can eat within one minute, so no extra food is left behind. Old, rotting food leads to lessened water quality. 

(Find out why goldfish need a filter in their tank.)

A Note on Stress 

Just like all other animals, fish can get stressed out. It leads to a breakdown of the fish’s health. Knowing what these signs look like will help you fix the problem. 

  • Look for a fish that has a decreased appetite.  
  • Also, look for other diseases such as ich taking place on the fish- this can also stress him out.  
  • Look for odd swimming patterns in your fish. You know what your goldfish look like when they swim. If you notice your fish doing odd things like crashing into the side of the tank, locking fins to the side, rubbing at ornaments or gravel, or otherwise engaging in odd behaviors, test the water quality. Remove the affected fish and remove any tank mates that may be causing stress to the fish. 

Immunocompromisation In Goldfish 

When your goldfish gets stressed out, their immune system lowers. 

Having a lowered immune system makes it harder for the goldfish to fight off common bacterial infections.  

As a result, a common bacteria that otherwise wouldn’t have affected the animal now becomes a huge threat.  

The bottom line? Keep the tank as stress-free as possible by keeping it clean and neat- and avoid overcrowding. 

fin rot in goldfish

What Are the Symptoms of Fin Rot?  

Understanding the symptoms of fin rot will put you at an advantage when it comes time to care for your fish. Look for these symptoms as you monitor your tank each day. It will help you catch fin rot early. 

Fins Are Discolored

You may notice fins turning colors; the most common ones sighted by fish keepers include fins that are black, brown, or white in color. It begins with the fins appearing to have milky edges.  

The change is quite subtle, so many fish keepers don’t even notice it at first. But as time goes on, the fins die and fall off, which leaves behind a tattered, ragged edge. 

Fins Become Shorter 

Some types of goldfish, such as the oranda or veiltail, are known for their long and flowing fins. If you see your goldfish’s fins getting shorter or simply not looking as beautiful as they usually do, it’s time to test the quality of the water or evaluate the tank size.  

Fins fall off because dead flesh is falling off of the afflicted fins. The area may also appear to be red and inflamed, and bloody spots may begin to show as the tissue is being eaten away. 

Fungal Infections Develop 

Secondary fungal infections may develop thanks to the fins becoming raw at the edges. One of the most common infections includes the columnaris or cotton wool bacteria, which is often present during the same time that fin rot affects the fish. 

(This could also be caused by ich or columnaris as well.)

Fins Develop White Dots 

These are a byproduct of the fins rotting away. Fin rot is most noticeable when you see an uneven, fuzzy white lining located on the fins’ and tails’ edges. Fins and tails may end up appearing milky or opaque. You might even see streaks of blood.  

Behaviors in Goldfish 

Goldfish behave in strange ways when they are affected by fin rot. The fish can actually feel their fins and tail dissolving away.  

The fish may look for relief by rubbing up against the tank itself and the decorations inside of the aquarium. If the fin rot is exacerbated as a result of nipping, the fish will be stressed out due to this bullying. 

(Other common diseases in goldfish include dropsy, swim bladder disease, constipation, and popeye.)

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How Do You Treat Fin Rot in Goldfish?  

Here are the steps for treating fin rot in goldfish!

Step 1: Know the Signs 

First of all, understand that fin rot is very common in goldfish, bettas, and other aquarium fish. The symptoms will vary from fish to fish, thanks to how long the animal has been affected. Here are the stages of fin rot to watch out for. 

  1. Stage 1: Fins and tail are showing some discoloration. Edges are especially affected. You may notice colors of white, red or black; this depends upon the original color of the affected fish.  
  2. Stage 2: Fin edges are frayed and uneven. Infected parts of the fin are beginning to fall off and die.  
  3. Stage 3: The tail or fin in its entirety has rotted away. The infection is attacking the rest of the fish’s body, and this could lead to the death of the fish. 

Step 2: Treat the Disease 

  1. Find out what environmental factors are causing the fish to get sick. If you do not remove the root cause of the fin rot, it is likely to come back. Begin by checking the quality of the water using a water test kit. Make sure the decor, other fish, and filter system are NOT the reason behind the fish feeling stressed out.  
  1. Separate the Sick Fish. Remove decorations, other tank mates, or clean/replace the filter system. Put the fish affected by fin rot into a quarantine tank. It is the first and most helpful step in treating a fish with fin rot. Once the fish is in the quarantine tank/hospital tank/sickbay, you will want to prepare a salt bath.
  2. Use two teaspoons of non-iodized salt per gallon of your hospital tank. You may also use methylene blue to (5% in solution) on the fins to help the healing process along.
  3. Another method is to bathe your fish in Tetracycline (250mg per gallon of hospital tank size) each day for one week, allowing the fish to swim in the solution for the duration of the day. You can then allow them to recover in a mild overnight salt bath.  
  1. Clean the main tank. Before you administer medication to the fish in your main tank, you want to do a water change, because most fish medications advise against doing them while fish are being treated. Clean the aquarium using a gravel vacuum, algae cleaner, and clean the outside of the tank, too. 
  1. Use medication on the main tank. You should speak to a vet to get the medicine that is best for your goldfish, but we use erythromycin as the remedy for our goldfish’s fin rot. If you notice a secondary fungal infection in your goldfish, methylene blue is another antifungal treatment that is appropriate for goldfish.
  1. Keep the Fish Comfortable. Make sure the tank is super clean and give the fish all he needs to recover. Make sure your air stone is working in top condition as some medications can make the water harder for breathing.  

Step 3: Recognize if the Fin Rot is Cured

Medication can take a few days to beat the disease. Look for the following signs that your fish is finally cured of its fin rot.  

  • The fin rot did not get any worse or progress 
  • There are no new symptoms of fin rot 
  • The appetite of the fish and his energy are coming back to normal levels 
  • The regrowth of fins has begun (they may be a new color, and this is OK) 

If you notice these things happening, congratulations- the fin rot should be gone. But you’re not out of the woods yet. Make sure you clean the aquarium at regularly scheduled intervals. Make sure you keep only enough fish as deemed safe by your tank size. Be sure you do not overfeed the fish.  

You should also make sure stress in the aquarium is reduced- keep temps to the proper level for goldfish depending on their species (too hot or too cold can stress them out).  

Make sure the water current is gentle. Get rid of any tank mates that may be causing grief to others. And monitor your fish daily using water checks and visual inspections to ensure everything is in order.  

fin rot in goldfish

How Do You Prevent Fin Rot?  

The good news is that preventing fin rot is not hard to do. You can enjoy a healthy tank of lovely goldfish with just some basic preventative maintenance. 

Visually Inspect Fish Each Day 

Take a good look at your fish every single day. What do you see? Write down their names and record what you see each day when taking a look. It will help you avoid minimizing the problem and will help you begin to notice patterns or changes in your fish, for better or for worse. 

Keep the Tank Clean 

Schedule a weekly cleaning of your tank. Just do it! It is the easiest way to prevent your fish from getting sick. You should also clean one aquarium decoration per week (cleaning them all at once could remove helpful bacteria from your tank).  

Set a reminder on your phone to do it each week at a set time, and it will become part of your routine in no time at all. 

Test the Water 

Invest in a good testing kit and test the waters each day. Record your findings in a notebook or Excel spreadsheet. It will help you notice and keep track of patterns over time and make it easy for you to fix a problem before it gets worse. 

Feed Appropriately 

Make sure the food you feed is within its date and that you only feed what your fish can eat in a minute. Leaving too much food to rot in the tank contributes to poor water quality. If you do feed too much, scoop it out as best you can.  

Break Up Conflict 

Is a fish attacking another fish? Time to get him out. You can put him in a different tank or give him to a good home. No matter how you do it, a fish that attacks another is going to cause stress, which will lower the immune system of the bullied fish and leave them open to diseases like fin rot. 

Check out this video about Goldfish fin rot!

Is Fin Rot Contagious?  

Yes, fin rot is contagious in goldfish. Here are the steps you can take to help prevent the spread of fin rot in your goldfish.  

  • Use a gravel filter to siphon the bottom of the tank; this will help get rid of any debris/waste in the tank. 
  • Now perform a water change of 25% on your fish tank.  
  • Now check and carefully monitor your water conditions. Use a good aquarium test kit to keep track of temperature, pH, Chlorine, nitrate, nitrite, and ammonia. You can take a sample of your water to a local fish shop for help or use that test kit we mentioned earlier. 
  • Place the affected fish into a quarantine tank for treatment. This tank should be bare-bones, a simple 10-gallon tank with filtration, and heating, if appropriate, will do just fine. Place the tank on a dark-colored table or surface as the dark color may soothe the fish. It also helps the fish avoid being nipped or bullied by other fish. 
  • Now treat the main fish tank using an appropriate antibiotic. You should talk to a vet to get the best antibiotic for your scenario, but we use erythromycin as the remedy for our goldfish’s fin rot and methylene blue if we notice a secondary fungal infection taking place.  
  • As you treat the main tank, make sure to remove the carbon from the filter. 
  • Now keep a close eye on your fish every day to ensure that the treatment is successful. Watch the fish in both your main tank and quarantine tank. If treatment goes as planned, you will notice the fins and tail growing back as the weeks go on. 

Is Fin Rot Fatal?  

Do not get into a panic if you notice your fish has fin rot. This disease is not deadly, but you have to act quickly in order to get it taken care of.  

It is a common disease among aquarium fish of all kinds; bettas, goldfish, and even tropical fish/saltwater fish can be affected. It is caused by bacteria that naturally occur in your fish tank. 

These bacteria in and of themselves are not inherently harmful, but they do become a problem if the fish’s immune system is compromised.  

The disease itself is very preventable, too. The two most significant factors in keeping fin rot out of your tank are responsibility and care on the part of the fish keeper.  

It means making sure you buy a tank that is appropriately sized for the amount and size of the fish you would like. Suppose you want to keep three Oranda goldfish. For three of these fish, a 40-gallon tank is ideal. It gives each fish ten gallons plus a little more to move around.  

You will also want to make sure the tank is outfitted correctly. You can keep fish feeling stress-free by offering plenty of hidey holes for the fish to relax in.  

Buy aquarium decorations that are safe but offer your fish a chance to rest and get away from tankmates and humans constantly in front of the tank. Like humans, fish sometimes just need their alone time.  

We’ve said it before, but we will say it again: Clean, clean, clean. Having a regular cleaning schedule plus an arsenal of cleaning products such as a ready supply of filters, gravel vacuum, and algae cleaning tools will be necessary to ensure the tank stays in great shape and gives your fish a healthy living space. 


The most important thing for you to remember is that fin rot is not uncommon. Thankfully there are tons of helpful resources such as this one to help you through this trying time.  

We encourage you to check out other awesome ways to keep your fish healthy by reading the other helpful articles on our website.  

Even if you’re not facing a problem now, you will have the knowledge at your fingertips to handle it should the need arise. Good luck and happy fishkeeping! 


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