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Argulus (a.k.a. Fish Lice)

Infected fish will have flattened, disc-shaped crustaceans measuring between 0.4 and 1.2 cm in diameter. These parasites may be visible anywhere on the body of the fish, including the eyes, gills and fins.


The parasitic crustacean Argulus (a.k.a. Fish Lice). Argulus adhere to the flesh by means of sucker-type discs. Once attached, the parasite pierces the flesh using stinger mouthparts and will suck the blood of the fish. Argulus inject a toxin that will kill smaller fish and leaves reddened, inflamed lesions on larger fish. This lesion often becomes infected. The intense irritation brought on by the Argulus parasite causes fish to rub or scrape against objects in the aquarium. Your fish may even try to jump out of the aquarium. Once the parasite has finished feeding it will swim freely in search of a new host and can survive for up to 3 weeks without a host.


Visible Lice should first be killed by dabbing them with Potassium Permanganate or an anti-parasitic medication. Then, they should be carefully removed from the fish using tweezers. It is paramount that you kill the parasite before attempting to remove it from the fish. It will make it easier to remove and less stressful to the fish. It is a good idea to then dab Methylene Blue on the lesions to prevent secondary infections. It is recommended that you feed your fish medicated food to prevent a bacterial infection from occurring. The whole aquarium will need to be treated to kill any unseen, free-swimming juvenile parasites. Fluke Tabs, Clout, Paragon, and Trifon work great.

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