Why Do Koi Fish Lose Their Scales? (Reasons & Solutions)

Koi fish are a popular species of ornamental fish that are often kept in outdoor ponds or indoor aquariums.

They are well known for their bright colors and patterns, and are known for their beauty and longevity.

However, koi fish can sometimes experience problems with their scales, which can cause them to lose their scales and become more susceptible to infection and disease.

Losing scales can be a sign of stress, illness, or parasites, and it is important to identify the cause in order to provide proper treatment.

In this article, we will discuss the causes and consequences of koi fish losing scale, as well as what can be done to prevent and treat this issue.

Koi fish lose their scales

Fish Scales & Its Functions

Fish skin plays an important role in the fish’s defense mechanism, providing a barrier against parasites and other external threats.

Some of the ways fish skin acts as a defense mechanism include:

Scales: Fish scales provide a tough, bony armor that can protect the fish from predators and parasites. The scales are also coated in a slime layer that can make it difficult for parasites to attach to the fish’s skin.

Mucus: Fish skin also produces a thick layer of mucus that can protect the fish from parasites and bacteria. The mucus can also create a barrier that makes it difficult for predators to grip the fish.

Pigmentation: Some fish also have pigmentation in their skin that can help to camouflage them and make them difficult to see.

Body temperature: They play a significant role in keeping the fish’s body temperature and buoyancy under control.

Spines and venom: Certain species of fish have spines or venomous glands on their skin that can be used as a defense mechanism against predators.

Immune system: Fish also have an immune system that can help to fight off infections and parasites.

Behavioral defense: Fish also have behavioral defense mechanisms, such as the ability to swim quickly or hide in rocks or plants, to avoid predation.

Age: Additionally, scales can indicate the fish’s age.

It’s important to note that fish’s defense mechanisms are not always 100% effective, and some fish can still fall prey to parasites or predators despite their protective skin.

Why Do Koi Fish Lose Their Scales?

There are several possible reasons why a koi fish might lose its scales. Some of the most general causes are discuss below:

Physical Injury

Physical injury can cause koi fish to lose their scales. Possibly if a koi fish bumps into a sharp object or is attacked by a predator, it can damage its scales and cause them to fall off.

In severe cases, the koi fish may lose a large number of scales, which can make it more vulnerable to infection and disease.

Beside It is necessary to keep the tank or pond free of sharp objects and to provide adequate protection for the koi fish, such as a screened-in pond or a predator-proof fence, to prevent physical injuries.


Infections, particularly bacterial or fungal infections, can cause koi fish to lose their scales.

These infections can be caused by dirty water, poor water quality, or stress, which can weaken the fish’s immune system and make it more susceptible to infection.

If a koi fish has a bacterial or fungal infection, it may develop red or white patches on its skin or fins, and its scales may become loose and fall off.


Koi fish can be infested with parasites, such as ich, which is also known as white spot disease. Ich is a common parasitic infection in koi fish and can cause them to lose their scales.

Ich is caused by a protozoan parasite that infects the skin and gills of the koi fish. It is characterized by the presence of small white spots on the skin and fins of the fish.

If left untreated, ich can cause severe damage to the koi fish’s skin and gills and can lead to death.

Nutritional Deficiency

Koi fish, like all animals, require a balanced and varied diet to stay healthy and maintain proper growth.

A lack of certain nutrients in their diet can lead to various health issues, including scale loss.

Scale loss can be a sign of a more serious underlying issue, such as a deficiency or an infectious disease, so it’s important to address the cause as soon as possible.


Koi fish are sensitive to stress and can be affected by changes in their environment or living conditions.

Stress can have a number of negative effects on fish, including an increased risk of infection and diseases, and it can also cause physical changes in the fish, such as scale loss.

Signs & Symptoms of Koi Scale Disease

The signs & symptoms of koi scale disease are,

  • Loss of color in the affected scales, which can appear light or white
  • Loss of scales, revealing underlying skin or tissue
  • Small holes or pits on the head and/or lateral line
  • Gasping for air at the water’s surface
  • Swelling or inflammation of the head and/or lateral line
  • Loss of appetite
  • Lethargy or listlessness

Early diagnosis and treatment can help to minimize the impact of the disease on your fish.

How to Prevent Your Koi Fish from Losing Scales

In order to prevent your koi fish from losing scale you have to take some precautions that must be helped.

There are a few key steps has been discuss regarding this issue:

Provide a balanced and varied diet

Providing your koi fish with a balanced and varied diet is an important step in preventing nutritional deficiencies and ensuring their overall health.

A high-quality diet should include a variety of commercial koi foods that are formulated to meet the nutritional needs of these fish.

In addition to commercial foods, you can also offer your koi fish a variety of fresh, non-toxic plants and small invertebrates as supplements to their diet.

It’s necessary to avoid overfeeding your koi fish, as this can lead to obesity and other health issues.

It’s also necessary to avoid giving your koi fish foods that are not suitable for them, as this can cause digestive problems and other complications.

Minimize Stress

Providing a spacious and properly-maintained living environment is important for reducing stress in koi fish.

This includes having sufficient space and hiding places for all the fish, as well as avoiding overcrowding and sudden changes in the environment.

By creating a stable and comfortable living environment for your koi, you can help them stay healthy and happy.

Regularly monitor water quality

Regularly monitoring and maintaining the water quality is an important aspect of koi care.

Proper filtration and aeration help to keep the water clean and oxygenated, which is essential for the health and well-being of koi fish.

By providing a clean and healthy environment, you can help prevent infections and other health issues that may lead to scale loss or other problems.

Consult with a veterinarian or fish care expert

If you have any concerns about the health of your koi fish, it’s a good idea to consult with a veterinarian or a fish care expert for guidance.

They can help you identify any potential issues and provide recommendations for how to prevent scale loss and other health problems.

Treatment for Losing Scales in Koi Fish

Treatment for scale loss will depend on the underlying cause.

Put infected fish in separate tank: If you notice that one or more fish in your tank are losing scales, it’s important to remove these fish from the tank and place them into another tank or container.

This will help to prevent the spread of any infections or parasites to the other fish, and also give the affected fish a chance to recover.

Parasites: If parasites are suspected, it is best to use a treatment specifically designed for the type of parasite present. It’s important to monitor the pH and temperature of the water, as these can affect the efficacy of the treatment.

Bacterial or fungal infections: If a bacterial or fungal infection is suspected, it is best to use an antibiotic or antifungal medication.

Environmental factors: Improving water quality and ensuring that the water temperature is within the optimal range for koi fish can help to prevent scale loss.

It’s also a good idea to monitor the water quality and examine the affected fish for signs of illness or injury.

Stress: Minimizing stress by providing a good quality of water and a suitable environment, as well as avoiding overcrowding, can help to prevent scale loss.


Why are my pond fish losing scales?

Fish that tend to swim erratically may damage themselves against hard sides and sharp edges, which can lead to scale loss.

To prevent scale loss due to damage from tank decorations, it’s necessary to choose decorations carefully and avoid using items that may be sharp or rough.

Do Koi Fish Scales Grow Back?

Yes, koi fish scales can grow back if they are lost or damaged. Scales are made of a hard protein called beta-keratin, which is similar to the material that makes up human nails. If a koi fish loses a scale, the surrounding cells will divide and differentiate to form new scales.

However, if the fish’s body is seriously injured or damaged, the scales may not be able to grow back properly.

Additionally, Koi can develop some diseases, mostly due to poor water quality, that can impede their scale growth.

Can fish replace lost scales?

Fish can replace lost scales, but the process can take some time and depends on the overall health of the fish and the reason for the scale loss.

If you notice that your fish is losing scales, it’s important to take action as soon as possible to address the underlying cause and promote healing. This could include making changes to the water quality or tank conditions, treating the fish with medication, or providing the fish with the right diet.

What causes raised scales on koi?

If a koi has advanced dropsy, it will be very noticeable due to the swelling and bloating of the body. The fluid buildup inside the koi’s body can cause the scales to lift away from the body, creating gaps between the scales.

Dropsy is a serious and potentially life-threatening condition that can be caused by a variety of factors, including infections, parasites, or organ failure. If you notice that your koi is experiencing swelling and bloating, it’s important to seek medical treatment as soon as possible.

Treatment for dropsy may include administering medication, performing water changes, and making adjustments to the living environment to improve water quality and reduce stress. In severe cases, it may also be necessary to provide supportive care, such as fluid therapy, to help the koi recover.

How is fish scale made?

Scales originate in the dermal layer of the fish’s skin. The dermal layer is tissue some cells beneath the outermost layer of skin (the epidermis) and is made up of blood vessels, nerves, and other structures.

In fish, the dermal layers also contain cells known as dermal papillae, whose development produces scales. Those cells use a protein called collagen which forms the hard, bony structure of the scales.

As the fish grows, new scales are added to the skin, while older scales are shed. This process of scale formation and shedding is known as scale remodeling.

What is fish scale good for?

Fish scales are used in jewelry and fashion accessories, such as earrings, bracelets, and necklaces.

Fish scales are also used in the production of cosmetics and skincare products, fish scale collagen is used as an ingredient in some anti-aging creams and other beauty products.

Are fish scales good eating?

Fish scales are generally not considered a food item and are usually not ingested. Fish scales are usually and customs removed from fish prior to cooking. While it’s not really dangerous to eat fish scales, many are not very appetizing and are often very difficult to swallow.

Fish meat and organs are generally regarded as more desirable to eat since they’re considered tastier and more digestible.

Are fish scales waste?

Fish scales can be considered waste in the context of the food industry because they are typically discarded during the cleaning and preparation of fish for cooking.

However, as I mentioned earlier, fish scales have a variety of uses in other industries such as cosmetics, jewelry making and traditional medicine, which can make them a valuable byproduct.

Some companies also process fish scales to extract collagen, which can be used in a wide range of products, including skincare and food.

In addition, there are initiatives to use fish scales as a resource rather than waste. For example, in some Asian countries, fish scales are being collected and processed to extract valuable compounds such as collagen, chitosan, and minerals that can be used in various industrial applications.

It’s important to note that fish scales are biodegradable, so when they’re not used for other purposes, they can be disposed of in an environmentally-friendly manner, without harm the environment.


  • Haryo, A., and R. Nurhidayati. ‘Pathology Change of Dropsy Syndrome in Koi Fish (Cyprinus Carpio) at IBAT Punten Batu’. Journal of Physics. Conference Series, vol. 1430, no. 1, IOP Publishing, Jan. 2020, p. 012011.
  • “Management for freshwater fish culture.” Food and Agriculture Organization of the United Nations.
  • Saint, Nicholas. “Diseases of Koi (Cyprinus carpio) – IAAAM1998.” VIN