Argulus(Fish Lice) Description, Symptoms, Life Cycle and Treatment

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Argulus(Fish Lice) Description

Argulus are a crustacean parasite in the subphylum Crustacea. This puts them in the same group with much larger crustaceans such as prawns and shrimp. Argulus is a member of the Branchiura class, which are all crustacean parasites. Argulus are one of the largest external parasites in home aquariums and ponds. Because of their size and visibility to the naked eye, they are also known as fish lice. The fish lice range in size from 5mm to 10mm in length. Even though they are quite large it can be difficult to see them sometimes because they like to hide in more sheltered areas on the fish host. The fish lice are round or oval in shape and almost flat. Kind of like a flattened horseshoe crab. The fish lice can move quite quickly and can swim between hosts.

Argulus Symptoms(Fish Lice Symptoms)

Symptoms include patches of irritated skin, gills and fins with small red holes. Because the argulus has hook like limbs and a sucking feeding apparatus, they can cause open wounds that can lead to secondary infection. This feeding apparatus releases enzymes to digest the host and this can also contribute to illness for the host fish. Of course another symptom of an argulus infection is actually seeing the parasites on your fish.


Argulus(Fish Lice) Life Cycle

Argulus have a direct life cycle using only the fish as hosts. They prey upon freshwater fish and marine fish. Argulus can spend a large amount of time swimming around and mating occurs when the male and female Argulus are swimming. The eggs clusters are dropped on any convenient submerged item. After hatching the Argulus makes several metamorphic changes as it goes towards adulthood. The entire cycle takes between 30-100 days depending on the temperature. After hatching they must find a host within a around four days or they will not survive.

Agulus(Fish Lice) Treatment

The most successful and effective treatments against lice are organophosphates. Using three treatments over the estimated life cycle of the parasite almost always eradicates lice. At typical summer pond temperatures of 68 degrees F or higher, treatments at 10-day intervals will kill existing adults and juveniles as well as emerging juveniles. Clout is one of the commonly available treatments and is quite effective.


There are no other treatments currently available that are likely to be totally effective. There is some suggestion that using a chitin inhibitor such as dimilin may stop the juveniles developing as they moult their exoskeleton but there has been no real testing done on this proposal.

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