enfermedades koi

My koi is sick. ¿Is that true?

What should I do if my koi does not eat ?

What should I do if my koi rubs ?

What should I do if my koi breathes heavily ?

What should I do if ….  ???


Do exactly the same what a doctor would do with you or with your child: Analyze the problem.

For a healthy koi applies exactly the same as for a healthy human being: a healthy life in a healthy environment with a healthy diet:

  • healthy living (e.g. no stress due to an overpopulated pond)
  • healthy environment (in a pond with optimum water parameters)
  • healthy diet (with quality food adapted to their size and seasons)

So “easy” …

Like humans, the koi is surrounded by aggressors (parasites, bacteria, viruses etc.). With the three points mentioned above, these attackers are not dangerous and will not harm your koi. BUT … when health components come to an imbalance, the fish may become ill.

enfermedades koi

My koi is sick …

Remember: “A stitch in time safes nine”.  Therefore, observing your koi is essential as long as it is done in a moderate way. With moderate I want to say, that it should not be exaggerated (checking the koi 10 times a day and panicking with any “abnormal” behaviour) nor perfunctory (e.g. feeding but without observing). As always, the solution is in the balance.

If one or more of the following symptoms occur during several days (3 or more) or several koi at once, then you should react:

  • rubbing (against walls, against aeration, against stones …)
  • jumping (a koi is not a dolphin! If a koi is jumping to the surface, is not a sign of joy)
  • constantly swimming against the inlet of water / air
  • separating from others
  • refusing food

From the time we are confident that “something is wrong”, we have to find out why.

NEVER administer any drug or product to your koi if you are unsure of the reason for the malaise.

enfermedades koi

Koi Hacienda: inflated koi

Here we indicate the most important questions to find the cause of the problem:

  • Does the filter work properly?
  • Do the UV lamps work well? (they have a limited lifespan !!!)
  • Is there enough oxygen? (in summer they need more)
  • How are the values of the water? (see specific section at the Koi Hacienda Academy)
  • Did you use any product (eg against algae)?
  • Did you introduce some new water plant?
  • Did you introduce some new koi?

If these questions do not have led to the origin of the problem, then we have to examine more closely …  under the microscope. Not exactly a device that everyone has at home. However it is necessary to thoroughly analyze the problem. Perhaps you know a doctor or pharmacist who could borrow it (take a sample and go there, would not be advisable, because the lifespan of parasites out of the water and away from the fish is very low).

How to take a sample of mucus?

  • Catch the koi
  • Take the koi with wet hands or surgical gloves (fine latex)
  • Take a slide
  • Pass the slide gently over the koi, starting behind the gills going towards the tail
  • Check that you have obtained enough mucus, if not, repeat the action elsewhere on the body of the koi
  • Cover the mucus on the slide with a cover glass
  • Use the extension 200 of the microscope (some parasites are very small eg costia)
  • If you find more than 7 parasites, you must act (1-3 parasites = harmless, 4-7 parasites = continue observing)

We will continue writing about koi diseases and how to remedy them.


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