Koi carp diseases: how to treat them?

The koi carp is a fish that can fall ill during its life. It is important that you react quickly by detecting the type of disease and using an appropriate treatment. Some diseases can spread rapidly to other fish in your pond.

These diseases can occur from one day to the next, following several factors:

• Overpopulation
• Stress to your fish
• Adding new fish
• Wounds that have become infected

In short, there are several factors that can explain the development of certain diseases in koi carp. It can involve several things:

• A parasitic attack
• A virological attack
• A bacterial problem

It is often one of these three causes. The first thing to do before treating is to make a proper diagnosis by means of a smear or a correct detection of the disease. There are not hundreds of veterinarians specializing in koi carp in France & Belgium. To properly manage your koi carp and their well-being, we recommend you read the Koi Doctor's bible (see below).

Symptoms: what is your koi telling you?

A sick koi almost always gives itself away through its behavior before lesions are visible. This table helps you guide your initial research. It does not replace a diagnosis: several diseases can produce the same signs, and a smear remains the surest way to identify a parasite.

How do you detect that your koi carp is sick? It is generally quite quick to notice. Indeed, your koi's behavior will be different in case of problems; it may not swim as it usually does and may lose its appetite. They may exhibit strange behaviors, such as rubbing against the edges or the bottom of your pond.

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Excessive rubbing may indicate parasitic attacks. Are your koi carp's eyes swelling? In the final stage, the abdomen swells. Some koi carp can develop chronic dropsy. To treat dropsy, it is advisable to use salt baths (not directly in the pond), or, by veterinary prescription only, antibiotic-based treatments (including in the form of medicated feed).

The most common koi carp diseases are:

• Dropsy
• White spot (Ichthyophthirius multifiliis)
• Carp pox
• Dactylogyrus
• Trichodina
• Chilodonella
• Costia
• Gyrodactylus
• Skin bleeding (viremia)

We generally distinguish two types of parasites: those found on the skin and the parasites present in the gills.

• DACTYLOGYRUS: Destroys gill epidermal cells. Fish group near aeration points. Can lead to high mortality. GYRODACTYLUS can also be found.

• CARP POX: This often involves the development of spots that look like wax. We advise using high-quality food like SAKI HIKARI to support the fish.

• TRICHODINA: This is a parasite that is often found and easy to observe under a microscope. These parasites feed on skin debris and create wounds that irritate the koi carp. How to treat a Trichodina parasitic attack? The most commonly used treatment is FMC or Chloramine T. It is advisable to carry out two treatments.

• WHITE SPOT: These white spots are actually parasites (Ichthyophthirius multifiliis). It often develops due to stress, moving, or a significant temperature change. One of the best solutions is an FMC treatment. Discover our treatments against white spot by clicking here.

• CHILODONELLA: Pollution by organic matter encourages the multiplication of Chilodonella. It is an oval parasite that infests the gills and mucous membranes of fish. This disease is fatal. Often, the fish will tend to stay at the surface for a long time before hiding motionless at the bottom of the pond. We recommend treating it with Kusuri Formalin, Alparex, or FMC.

• COSTIA: These are single-celled organisms that can be present on the fish's skin. This parasite produces skin sores and infections. It is known as the "weakness parasite" and attacks koi carp whose immune system is weakened. You can use a salt bath in a quarantine tank.

• GYRODACTYLUS / Treatment with LERNEX: Gyrodactylus, or skin flukes, are metazoan parasites (which consist of multiple cells) that attach themselves to the skin of fish thanks to their hooks.

• ANCHOR WORM / This is a skin parasite that looks like a small white rod. To treat anchor worm, you can use various solutions such as MEDOPOND or LERNEX PRO. Be careful, however, to strictly follow the instructions for this type of product and to analyze the water.

• ARGULUS (FISH LOUSE): This is a parasite often visible to the naked eye. This crustacean has a fairly flat circular shape bearing four pairs of legs on its sides. You can use LERNEX or FLUKE-M. Ask a specialist for advice on treating this type of parasite.

• BACTERIAL ATTACK / Some fish can catch a bacterial attack; one of the most natural solutions is to limit bacterial pressure by performing water changes. You can also use treatments in quarantine tanks with the use of salt.

Before any treatment: the 5 checks

A poorly prepared treatment can do more damage than the disease itself. Before pouring anything into the pond, take a few minutes for these checks:

1. Analyze the water: ammonia, nitrites, pH, and KH. Degraded water weakens fish and can make some products more aggressive. Our guide how to perform a water analysis details the method.
2. Calculate the actual volume of the pond, including the filter. A dosage calculated on a volume estimated "by eye" is the most common mistake.
3. Reinforce oxygenation: many treatments reduce available oxygen. An air pump running for the entire duration of the treatment is a good precaution.
4. Read the instructions: some products require switching off the UV-C, removing activated carbon, or avoiding salt. Never mix two treatments without a specialist's advice.
5. Isolate if possible the most affected fish in an aerated and filtered quarantine tank.

Quarantine and salt bath: the prudent method

As the article mentioned above: salt is preferably given in a bath or quarantine tank, not directly in the pond. A separate tank protects the plants, allows for close monitoring of the fish, and avoids exposing the whole pond to a treatment.

• A clean tank, filled with pond water to avoid temperature or pH shock.
• Continuous aeration and small filtration.
• Non-iodized salt, intended for ponds, dosed according to the product sheet.
• Daily monitoring: in case of distress (fish lying on its side, gasping for breath), put it back in non-salted water.
• Any new fish also spends several weeks in quarantine before joining the pond.

How to prevent koi carp diseases? Even under very good conditions, it is possible for diseases to develop.

• Good water quality
• A well-sized filtration system
• Quality food
• Beware of overpopulation

How to treat koi carp? Here is a list of products that allow you to treat koi carp diseases. On the left in the filters, you can easily select your water volume and the type of disease.

Then, you just need to choose an appropriate treatment. We invite you to seek the help of a professional and perform a microscope examination to be sure to treat the right parasite. Any treatment is sensitive for the fish and can weaken the most affected ones. It is also very important to provide the dosage perfectly adapted to your water volume.

Frequently asked questions about koi carp diseases