"what's on my fish" ?

Gill Fluke (Dactylogyrus),

Gill flukes. are visually similar to skin flukes with both species attaching themselves to the body of the fish to feed on upper layers of skin and gill tissue.

Koi can become infected with both types of flukes at the same time, but it is more common for just a single type to start causing problems unless water conditions are particularly bad.

Since flukes are microscopic, the only way to determine if your koi are infected is to take a skin/gill scrape and check under a microscope, or to try to identify common behavioural and appearance changes caused by the parasites.

Like many other types of parasites, flukes are specific to different types of fish, and koi will have their own particular fluke that specializes in carp.

Flukes can attach themselves to other fish for a short time, but they would eventually need to find the correct host to survive and breed. Luckily, flukes are more of a nuisance to koi in the early stages and should not cause any long-term problems with health if treated quickly.

Flukes by themselves will irritate the fish, and will gradually stress the koi leading to them eating less and acting strangely.

As the number of flukes grows, koi will become weaker and the flukes will start spreading to other fish, so it’s always good to treat any possible fluke outbreak early to stop the problem from escalating

Gill flukes are the type of fluke you more commonly hear about, as they’re easier to identify in both visual appearance and symptoms.

They’re larger than skin flukes, measuring up to 3mm in length, but you will still need a microscope to properly identify them as they’re transparent and still too small for the naked eye.

Gill flukes have a slender cylinder body shape, with dark spots on the head of the body which skin flukes do not have.

They also have a set of hooks known as an “opisthaptor”, which is a specialized organ for attaching itself to the tissue of fish.

Both flukes have these hooks which are similar in shape, so the easiest way to identify the difference under a microscope is the dark spots present on the gill fluke.

Also, unlike skin flukes, as their name suggests, gill flukes attach themselves primarily to the gill tissue of fish rather than the body.

Within the gill, they feed off mucus excretions and tissue and can cause open wounds, ulcers, and even infection from bacteria and fungus if they’re left untreated.

Common Gill Fluke symptoms include:

Rubbing against pond liner/objects

Constant “chewing” behaviour

Irritated gills or ulcers forming (wounds)

Dulling in colour


Koi not taking food