Visible Parasites Affecting Koi Health

Koi, like all other fish species, are susceptible to a number of parasites and their negative impact on the body. While some are unobservable to the eye, many parasites are easily discernible and can be identified for quick and effective treatment.

There are some parasites which attack the Koi and cause observable damage to the skin, scales, gills and fins of the species which if not treated in time, can even lead to severely dangerous health conditions.

Argulus Or The Fish Louse

It is a parasite which is around 1 cm wide, and they stick to the skin of the Koi with the use of suckers and use needle like mouth features to inject a toxin into the fish. The Argulus causes extreme irritation and discomfort to the Koi, causing them to jump and scratch, which usually results in a bacterial infection.

If the Argulus affect the gills of a Koi, they can cause severe damage and even death of the affected specimen.

White Spot Or The Ichthyopthirius Multifilis

The parasite causes visible white spots to develop on the gills, fins and skin of a Koi, which are actually protozoan cells which develop underneath the skin and consume the cells and body fluids of the affected fish.

Koi experience a need for scratching along with the visible white spots on the skin, and also exhibit a reduction in consumption rate and lethargy. If left untreated, it can prove to be fatal for the Koi.

Anchor Worm

It is a parasite which can reach to a size of around 10 to 12 mm. The anchor worm burrows into the Koi tissue underneath a scale, and the tail and body of the worm are the usual visible parts of the parasite. Bacterial and fungal infection can also be caused around the affected area adding to the discomfort of the Koi.


It is the condition which involves the swelling of the scales of the Koi. It gives the body of the fish an appearance of a pine cone, and if the swelling is observed in the specimen gradually, then parasites might be one of the most probable reasons for the abnormality in the physical condition of the Koi.

Gill Maggots

These parasites are the Ergasilus, and have a grayish black and white appearance and can reach up to several millimeters in length. They infest the gills of a Koi, and severe infestations can result in serious conditions like the erosion in gill filaments, which increases the probability of a secondary infection.

These visible parasites need to be treated at once to protect the Koi from severe complications and pond contamination.