Koi Flukes

Freshwater flukes occur in all parts of the world on numerous species of fishes. By their name, you might expect them to be visible to the naked eye, however, they are microscopic.

Flukes occur in two major classes, that is; Dactylogyrus, the famed Gill Fluke, and the second class is Gyrodactylus, the Skin fluke. There are certain morphological differences between these two classes. Under the microscope, you would notice that the Dactylogyrus fluke has several pairs of eye-spots, and they also lay eggs. In a specimen of Gyrodactylus, you would only see an embryo inside, with no eyespots in the adult.

In the summer, one adult Dactylogyrus fluke can produce 2,320 individuals in only thirty days.

One adult Gyrodactylus can produce 2,452 individuals within 30 days during the summer.

Most flukes agree that the best place to live is on the surface of a fishes' skin or gills, feeding on blood, and mucus found there. In my studies of these parasites, I have found considerable overlap of the different species on a single fish. Dactylogyrus seems to have no qualms about showing up in a skin scraping, and Gyrodactylus seems to have equal affinity for the gills.

Flukes are easy to diagnose microscopically. A skin scraping should be taken with a plastic cover slip from under the chin, between the gill covers. Another sample should be collected from the side of the body; scraping from there and out onto the tail and off the tip.

Their primary mode of killing would ostensibly be through the accumulation of large numbers. Especially in fish fry, the numbers of flukes encountered are accepted as the cause of mortality simply because they take such a toll on the victim when they occur in large numbers. Based on observations made in practice, however, I would like to introduce my opinion of how just a few flukes can kill a larger fish.

Control of flukes has become increasingly easy with contemporary medicine. Praziquantel works well.

Repeat dosing to control their life cycle is important. Since their life cycle can be completed in four days, it's important to treat several times for Flukes.

Supplemental Reading

A Pond Keepers Number One Parasite Enemy