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10 Reasons Your Koi Fish Is Losing Its Scales And How To Stop It!

Koi are a beautiful fish that are often seen in Japanese gardens and koi ponds. They are a member of the carp family and can live for many years, reaching up to three feet in length. Koi are usually black, white, or yellow, but can come in a variety of colors and patterns.

With the popularity of keeping koi ponds and the price tag for koi fish increasing, all koi keepers want to ensure that their fish are in the best of health!

Unfortunately, we have seen a number of people reaching out and asking questions about their koi losing scales in the last couple of months so we have decided to publish this article.

We hope that this list of the more common reasons that your koi fish can lose its scales will be able to help as many of our readers as possible better understand what they should be keeping an eye out for in their koi pond.

Some of these conditions can be reversed without causing issue to the fish but other problems may require some serious treatment to fix.

The Koi Living In Poor Water Parameters!

The most common cause of koi fish losing their scales is due to the koi living in poor water conditions. This can include a koi pond that doesn’t have enough filtration, the koi not having enough surface area to breathe, or the water being too dirty.

When koi are living in water that isn’t clean, they will often start to lose their scales as their immune system becomes compromised.

The first place you will notice this is often around the head and mouth area as these are the places that koi use to breathe. If you see your koi rubbing its head on rocks or other surfaces in the pond, this is a sign that the water quality isn’t good enough and you need to take action!

The koi will also stop eating as they are trying to avoid taking in any more toxins through their food. If your koi stops eating, this is a sign that something is wrong and you need to check the water quality immediately.

You can test the water quality yourself with a simple test kit or by sending a sample of your pond water to a koi dealer or veterinarian.

Common water parameter issues include:

  • Ammonia levels that are too high.
  • Nitrite levels that are too high.
  • Nitrate levels that are too high.
  • pH that is out of balance.

Any of these issues can cause your koi to lose its scales so it’s important to test the water and make sure that the levels are all within expected levels.

Koi Living On A Low-Quality Diet!

Another common reason that your koi may end up having problems with its scales peeling is due to a low quality diet. Koi are omnivorous fish, which means that they need both plant and animal matter in their diet to stay healthy.

A koi diet should be made up of a high-quality koi food that contains all of the nutrients that koi need to stay healthy.

In addition to a high-quality koi food, koi should also be given occasional treats of live or frozen foods to help them get the protein that they need.

A koi diet that is lacking in nutrients will often lead to koi losing their scales as their bodies are trying to conserve energy. This can also lead to koi becoming more susceptible to disease and other health problems.

Other symptoms of a koi fish being on a low quality diet include:

  • Fading colors.
  • Loss of appetite.
  • Lethargy.

If you suspect that your koi’s diet is the reason that it is losing its scales, you should switch to a high-quality koi food and make sure that they are getting enough protein in their diet. You can give koi live or frozen foods

An Infection On The Koi!

Infections on koi can be common and some types of infections can result in the fish having problems with its scales. The most common type of infection that koi get are fungal infections, which often appear as white spots on the koi’s body.

Other types of infections that koi can get include bacterial infections, viral infections, and parasites. These types of infections can often result in koi losing their scales as the fish’s body is trying to fight off the infection.

If you think that your koi may have an infection, you should take it to a koi dealer or veterinarian for treatment. Some infections can be treated with medication while others may require surgery to fix the problem.

A Koi With A Hormonal Imbalance!

Koi fish can sometimes have problems with their scales due to a hormonal imbalance. This is most common in koi that have not been properly sexed and are kept in mixed-sex groups.

When koi are kept in mixed-sex groups, the males will often produce too much of the hormone testosterone. This can result in the fish having problems with its scales as the hormone affects the fish’s ability to shed its old scales.

If you think that your koi may have a hormonal imbalance, you should take it to a koi dealer or veterinarian for treatment. Hormonal imbalances can often be treated with medication surprisingly easily in most cases.

Do Your Koi Have Dropsy?

Dropsy is usually rare in koi fish but if they do get dropsy, they are almost guaranteed to have problems with their scales. Dropsy is a condition where the koi’s body swells up due to an accumulation of fluid.

This can often cause the koi’s scales to pop off as the fish’s body swells. In some cases, the koi may even have its internal organs pushed out through its mouth or vent due to the swelling.

Dropsy is a serious condition and koi that have it need to be treated immediately. If you think that your koi may have dropsy, you should take it to a koi dealer or veterinarian for treatment as soon as possible but unfortunately, bad cases of dropsy can kill your fish with days.

The Cuticle Of The Koi Is Damaged!

The cuticle of a koi fish is a clear, protective layer that covers the koi’s scales. This layer is what helps to keep the koi’s scales attached to its body and when it is damaged, the koi’s scales can start to fall off surprisingly quickly.

The cuticle can be damaged in a number of ways but the most common cause is usually due to the koi rubbing up against something in its environment. This can often happen when koi are kept in ponds with rocks or other hard objects.

If you think that the cuticle of your koi’s scales is damaged, you should take it to a koi dealer or veterinarian for treatment. In some cases, the cuticle can be repaired relatively easily and your koi will be back to normal in no time.

Stress And Anxiety In The Koi!

Just like humans, koi fish can also suffer from stress and anxiety. This can often be caused by a number of different factors such as:

  • Poor water quality.
  • A lack of food.
  • A bully koi in the pond.
  • Not enough hiding places.

If your koi is stressed or anxious, it can result in the koi losing its scales. This is because the koi’s body is trying to rid itself of the stress and anxiety, and one of the ways it does this is by shedding its old scales.

The issue is, when your koi fish is stressed or anxious, it may not replace these old scales that it sheds. This can result in your koi’s body becoming increasingly naked over time and eventually, the koi may die if the problem is not fixed.

If you think that your koi is stressed or anxious, you should take a look at its environment and see if there are any changes you can make to help reduce the stress and anxiety levels

Trauma To The Body Of The Koi!

Koi fish are surprisingly fragile creatures and even a small amount of trauma to their bodies can often result in the koi losing its scales. Some common causes of trauma to koi include:

  • Being attacked by a predator.
  • Being hit by a rock or other hard object.
  • Running into something in the pond.

If you think that your koi has suffered some trauma, you should take it to a koi dealer or veterinarian for treatment. In most cases, the koi will need some time to recover from the trauma but if it is treated quickly, the koi should make a full recovery without any problems.

Some of the factors that we have covered above can make a koi fish more susceptible to trauma such as the fish being on a poor diet. The lack of essential nutrients in the diet of the fish can make the koi’s body weaker and more prone to injury.

A koi fish that is kept in a dirty pond is also more likely to suffer from trauma as the koi can be more easily attacked by predators or can run into things in the pond more often.

Predators Attacking Your Koi Fish!

Although this can come under the trauma section above, we actually wanted to give predators attacking your koi fish its own section. Too few people actually realize just how many predators will try to attack your koi, especially younger, smaller koi in a well kept koi pond due to how clear the water is.

Some of the most common predators that will try to attack your koi include:

Birds – Herons are probably the most common predator of koi but eagles, ravens, and even seagulls have been known to go after koi fish.

Mammals – Raccoons, opossums, mice, rats, and even cats have been known to attack koi fish.

Reptiles – Snakes, turtles, and even lizards have been known to attack koi fish.

As you can see, there are quite a few predators that will try to attack your koi fish and if you have a koi pond, you should do everything you can to protect your koi from these predators.

One of the best ways to protect your koi from predators is to make sure that the koi pond is well covered. This will stop most birds from being able to get to your koi and will also make it more difficult for mammals and reptiles to get to your koi.

You should also make sure that you remove any potential hiding places for predators such as overgrown plants or rocks near the edge of the pond.

Predators will often use these hiding places to launch an attack on your koi so by removing them, you will make it much harder for the predators to get to your koi.

Another great way to protect your koi from predators is to use koi netting. This is a special type of netting that is designed to protect koi fish from predators and it can be an invaluable tool in protecting your koi fish.

Plants and rocks can provide koi with the perfect hiding place from predators but they can also provide koi with the perfect place to hide from you so there is a trade off.

Old Age Setting In!

As with all animals, older koi fish can end up having a wide range of problems with some of them resulting in scale loss in the fish.

This is one of the less common reasons that your koi fish will end up losing their scales though so it is usually not a problem for the majority of people.


That brings our article going over why your koi fish can lose their scales to an end. If you have noticed that your koi fish is losing its scales, then it is important to try and figure out the cause so that you can treat the problem quickly. We hope that you have found this article helpful and that you now have a better understanding of why koi fish lose their scales.