Argulus (Fish Lice)

Argulus, commonly called fish lice, is a genus of branchiuran crustacean parasites that attach to the skin, fins, and gills of freshwater and some marine fish. About 5 to 10 mm across and clearly visible to the naked eye, they move across the host, pierce the epidermis with a proboscis, and feed on blood and tissue fluids. Heavy infestations are expressed through focal ulcers, hemorrhages, excess mucus, secondary fungal and bacterial infections, chronic stress, poor growth, and in severe cases mortality of fry and juveniles. Argulus also acts as a mechanical vector for viral and bacterial pathogens and for trypanosomes. Its life cycle includes off-host egg-laying on hard substrates, so hatchery troughs, pond walls, and equipment harbor egg clutches that resist drying for extended periods. For producers, fish lice are a recurring problem in freshwater ponds, tanks, and ornamental systems, especially where wild fish or birds have access. Control combines manual removal where feasible, pond drying and liming to kill eggs, and treatments such as organophosphates, diflubenzuron, or salt where permitted. Screening intakes and excluding wild fish break the reinfection cycle, since Argulus species have low host specificity.