Fish Lice

Fish Lice on Koi

Parasites are not uncommon to koi. In fact, fish parasites exist in virtually every body of water where fish are present. One such koi parasite is the Argulus, or Fish Lice. Just like the Anchor Worm, Fish Lice are a crustacean. In a koi pond lice are visible only if they are adults, the juvenile are microscopic but will become visible at approximately 6 weeks of age.

The adult Fish Lice parasite is flat and oval shaped with four pair of legs used for swimming. It looks like a glob of clear jelly infused with pepper. The eyes are recognizable on the face as two prominent black specks. It has suction type discs used to adhere to the host. Fish lice on koi are quite mobile; you can actually see them move along the fish’s skin. They can even swim from one fish to another if they so choose. A fish lice parasite can actually live for several weeks without attaching to a host fish! Adults may grow to ½ inch in size. The female leaves the host fish to lay her eggs onto plants and anything else in your pond. She releases up to 500 fertilized eggs at a time. These fish lice eggs will hatch in two to eight weeks, depending on water temperature.

Fish lice have tiny mouthparts that are stingers. These stingers are used to pierce the flesh and dine on the koi’s blood and mucus. The louses constant movement coupled with constant stinging cause your koi’s skin to become red and irritated. As the lice move around on the fish it leaves open holes in the koi’s slime coat which allow bacteria to infiltrate the skin and cause havoc, generally resulting in sores or ulcers.

What are symptoms of koi lice?

If your fish are rubbing or scraping the pond sides and twisting as if to shake something off its back you probably have a koi lice pond infestation. If you think you see freckles that move on your koi fish lice are probably infecting your pets.