Fish Lice or Argulus





I was called out to a pond where all the small fish were dying.

Because it was mainly the smaller fish, I suspected parasites, specifically Argulus(fish lice) or fluke.

However, I could not see any lice on the fish, so I did a scraping and found small fish lice with a microscope. I normally treat fish lice with Dipterex (10 g / 10 000 liters) because it is cheap and very effective against lice, so I did so, however, it did not clear the fish from the lice.

After investigating, I heard that the hobbyist treated his pond with Dipterex almost every two weeks, (weak solution of 10 grams per 15 000 liters) because he had various problems with lice and Anchor worm for more than a year.

This explained the fact that I could not see any lice with the naked eye and I immediately realized that the lice became immune to the Dipterex due to the constant treatment.

I treated with Dimilin (10 grams / 10 000 liters) and it immediately cleared the fish from lice. I will do a follow up treatment to sort out the juveniles hatched after my initial treatment.

It just shows you that we have to be cautious of using weak treatments or ongoing treatments, and we should stick to the prescribed dosages.

Do you need to repeat the treatment a few times before the parasites are completely cleared out?

Two treatments a week apart is normally sufficient.