Koi Fish Diseases

koi fish diseases
koi fish diseases south africa

Koi Fish Diseases

Koi fish, also known as Nishikigoi, is a type of domesticated carp that are often kept in ponds and water gardens. While they are hardy and resilient, they can be prone to certain koi fish diseases. It’s important for koi owners to be aware of these diseases and how to prevent and treat them.

Many pond owners believe that koi fish diseases are mainly introduced and passed on by sick fish. Fortunately, this is very rarely the case and it’s mostly up to you whether your fish keep well and fit. More than 90 % of the diseases are caused by inappropriate living conditions, such as water values and inadequate nutrition!

List of Koi Fish Diseases




Fish Lice (parasites)

Trichodina (parasites)

Ulcers (bacteria)

Chilodonella (parasites)

Costia (parasites)


Sick Koi Fish Signs


Changes in temperature or light exposure, cramped swimming room, not having the right number of fish, and more can stress your koi, weakening their immune system and making them more susceptible to disease.

One of the most obvious signs of koi fish diseases is changes in color or marking. If your koi’s colors become dull or faded, this could indicate a possible health issue.

Behavioral changes can also indicate a possible health issue with your koi fish. If you notice that your fish is swimming erratically or listlessly, this could be an indication that something is wrong with them. It is also important to note any changes in appetite as well and if your koi are hiding.

Keep an eye out for physical deformities such as discolored eyes, open sores on the body, protruding scales, and gills that appear swollen or red.


Clean And Healthy Environment


In order to prevent koi fish diseases, it’s important to maintain a clean and healthy environment for them. This includes regular testing and adjusting the water quality, providing proper filtration and aeration, and performing regular water changes. It’s also important to quarantine any new fish before introducing them to the pond, to ensure that they are not carrying any diseases.

Your Koi rely on you to provide a healthy environment in their pond and to ensure that their lives are stress-free. Diseases in koi usually result from the following issues:


          • High Ammonia Levels In The Water
          • Low Oxygen Levels
          • Handling The Fish
          • Poor Water Quality
          • Overcrowding In The Pond
          • Parasites
          • Incorrect Water Temperature
          • Toxic Chemicals
          • Sharp Edges In And Around The Pond
          • Inadequate Or Incorrect Nutrition


Koi fish can be prone to certain diseases, and it’s important for koi owners to be aware of these diseases and how to prevent and treat them. Keep the water conditions optimal by maintaining a clean and healthy environment, performing regular water changes, and quarantining new fish before introducing them to the pond. These steps can help to keep your koi fish healthy and prevent disease infestations.




Another important step is to quarantine any new fish before introducing them to the pond. This will help to prevent the spread of koi fish diseases and parasites and will allow you to observe any potential symptoms of illness in the new fish before they are introduced to the rest of the population.