Koi carp diseases: how to treat them?

It is often one of these three causes. The first thing to do before treating is to make a proper diagnosis using a smear or by correctly identifying 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 reading the Koi Doctor's bible (see below).

Symptoms: what is your koi telling you?

A sick koi almost always betrays itself through its behavior before lesions become visible. This table helps guide your initial research. It does not replace a diagnosis: several diseases can show the same signs, and a smear remains the most reliable way to identify a parasite.

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

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Intense rubbing can indicate parasitic attacks. Are your koi carp's eyes swollen? In the final stage, the abdomen swells. Some koi carp can develop chronic dropsy. To treat dropsy, it is recommended to use salt baths (not directly in the pond), or, on veterinary prescription only, treatments based on antibiotics (including in the form of medicated food).

The most common koi carp diseases are:

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

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

• DACTYLOGYRUS: Destroys the cells of the gill epidermis. Fish gather near the aerators. Can cause high mortality. GYRODACTYLUS can also be found.

• CARP POX: This often involves the development of patches that look like wax. We recommend using a quality food such as 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 recommended to perform two treatments.

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

• CHILODONELLA: Pollution with organic matter promotes 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 and then hide motionless at the bottom of the pond. We recommend treating it with Kusuri Formaline, Alparex, or FMC.

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

• GYRODACTYLUS / LERNEX treatment: Gyrodactylus, skin worms, are metazoan parasites (which contain several cells) that attach to the fish's skin with their hooks.

• ANCHOR WORM / This is a skin parasite that looks like a small white stick. To treat anchor worm, you can use different solutions such as MEDOPOND, LERNEX PRO. However, be sure to follow the instructions for this type of product and test the water.

• ARGULUS (CARP LICE): This is a parasite often visible to the naked eye. This crustacean has a fairly flat circular shape with 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. Test the water: ammonia, nitrites, pH and KH. Degraded water weakens the fish and can make certain products more aggressive. Our guide how to perform a water test details the method.
2. Calculate the actual volume of the pond, filter included. A dosage calculated on an estimated volume "by eye" is the most common error.
3. Increase oxygenation: many treatments reduce available oxygen. An air pump running throughout the treatment is a good precaution.
4. Read the instructions: some products require turning off the UV-C, removing the activated carbon, or avoiding salt. Never mix two treatments without the advice of a specialist.
5. Isolate if possible the most affected fish in an aerated and filtered quarantine tank.

Quarantine and salt bath: the cautious method

The article reminds us above: salt is preferably given in a bath or quarantine tank, not directly in the pond. A separate tank protects the plants, allows you to monitor the fish closely, and avoids exposing the entire pond to a treatment.

• A clean tank, filled with pond water to avoid a 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.
• Every new fish also goes through quarantine for several weeks before joining the pond.

How to prevent koi carp diseases? Even under very good conditions, diseases may break out.

• A good water quality
• A well-sized filtration system
• Quality food
• Be careful 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 will just need to choose a suitable treatment. We invite you to seek the help of a professional and perform an examination under a microscope to be sure of treating the right parasite. Every treatment is sensitive for the fish and can weaken the most affected among them. It is also very important to plan the dosage well adapted to your water volume.

Frequently asked questions about koi carp diseases