Fish lice (Argulus spp) on wild Barramundi (Lates calcarifer), Finniss River, NT

Fish lice are external parasitic crustaceans that infest freshwater fish. They belong to the genus Argulus and are usually known as fish lice (louse) due to their flattened, oval-shaped bodies.They attach themselves to the skin, fins, and scales of fish using hooked appendages  or sucker-like appendages, and feed on the body fluids of their host.

They can cause irritation, inflammation, and secondary infections in fish, leading to reduced growth, decreased immunity, and in severe cases, death.

This video was filmed in the upper reaches of the Finnis River in the Northern Territory of Australia. The fish were often seem to be brushing up against vegetation and branches in what appears to be an attempt to dislodge the lice.

Fish lice are considered harmful parasites in aquaculture and  commercial fisheries and proper identification and control measures are necessary to mitigate their impact.

Video copyright Greg Wallis 2023