Fish Lice, or Argulus – Branchiurian Parasites

Fish Lice, or Argulus

Different names for the same parasite. This is a crustacean / copepod parasite, meaning it’s a lot like a little crab. Little? Yeah, it’s about 1/4 inch or less, in diameter and they are EXTREMELY agile. I plan to upload a movie with these, so you can see it. (See below)

Argulus aka Fish Lice

Where present, this parasite is commonly seen in the Fall of the year. Folks call me and say “My fish has a freckle.”

Hmmmm A freckle? Well that happens sometimes, it’s called Shimi, and hard water causes it.

The next day, they call back. “Remember that freckle? Well it moved to someplace else on the fish! ”

So, moving freckles…..usually that’s Argulus!

Argulus fish lice copepod symptoms and treatment
Argulus fish lice copepod symptoms and treatment

Argulus is introduced on fish, or in water containing immature, freeswimming forms of the parasite. The parasites go through several sheds, or molts of their skin until they’re ‘adult’ versions that look like these images and you can see them with the un-aided eye.

Argulus has two “suction cups” on it, to help it hold onto the fish. Then when it’s in position, it drives a hollow feeding needle into the fish and drinks blood and plasma. It damages the skin and opens it up to infections. It’s very stressful.

It’s treated with serial applications of a VERY safe medicine called a “gyrase chitin synthesis inhibitor” which are harmless to beneficial bacteria in the system, and to the fish. There are several on the market as listed below.

Treatment one from Microbe-Lift (Click)

Treatment two from Hikari (Click)

Both of the above are very very similar. They’re very safe.

Anchor Worm and Fish Lice (Argulus) Video

Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.