Hidden Parasites And Koi Health

In order to protect your pet Koi from any possible attack of parasites, it is important to be observant and recognize the symptoms highlighting the precarious health conditions of a specimen. While some parasites are visible with the naked eye, there are a number of others, which are microscopic or so minute that it requires constant observance and a watchful eye to identify the symptoms in an affected Koi, and provide it with the required treatment.

Some of the most common protozoal parasites need to be identified underneath a microscope, and exhibit certain physical symptoms and behavioral modifications in Koi.


It is a protozoal parasite which affects the skin and gills of the Koi. It causes the skin to adopt a whitish opaque appearance, while the affected specimen demonstrates symptoms which include lethargy, flashing and rubbing.

Trichodina causes tissue damage as it moves through the mucus.


It is a very tiny flagellate which affects the skin and gills of a Koi. This parasite can cause a very rapid infestation and the affected specimen showcases a range of symptoms, which includes clamped fins, opaque white skin, rubbing, lethargy and flashing.

Costia is often observed on Koi as a form of a secondary parasite.  


Flexibacter columnaris is a bacterium which causes the cotton wool disease. The disease causes white tufts to develop around the mouth region of the fish, which spreads to the fins and body of the specimen leading to a thin appearance as well as ulcers.

The bacterium enters a fish through the gills and small wounds, and is a risk because of causing a highly contagious disease.   


It is a protozoan which can reach a size of 40 to 60 microns, and is severely dangerous for the species. Chilodonella causes the skin to take on an opaque appearance which is mostly observable in the area between the head and the dorsal fin region.

In severe cases, the skin tends to look swollen, while the parasite can attack and completely destroy the gills of a specimen as well, which results in the death of the affected Koi.  


These parasites are live bearers as well as egg layers, and attack the skin and gills of fish. They have a usual size range of around 0.05 to 3.0 mm in length. Flukes are not observable through the naked eye, and they attach themselves to the skin and gills of their victims through the use of hooks.

Koi, which are attacked by flukes, exhibit symptoms which include jumping, flashing and rubbing against various objects to rid themselves of the irritation caused by their presence.

It is very important for a Koi pet owner to observe the apparent symptoms of their fish, as microscopic parasites are impossible to identify without the suitable equipment, and failure to provide prompt treatment can increase the fatality rate of your pet life.