Argulus

Argulus is a genus of small crustacean ectoparasites known as fish lice. They belong to the class Branchiura, within the phylum Arthropoda. Argulus species are external parasites that infest a wide range of freshwater and some marine fishes worldwide. Notable species include Argulus foliaceus (the common fish louse) and Argulus japonicus (the Japanese fish louse).

Biology and life cycle: Argulus attaches to the skin, scales, fins, or gills of hosts using suction cups and by feeding with specialized mouthparts. They feed on blood and tissue, causing irritation and tissue damage. Eggs are laid in gelatinous masses that attach to submerged surfaces; the eggs hatch into free-swimming nauplius larvae, which then molt to copepodids and eventually attach to a host as adults. The life cycle allows relatively rapid population build-up under favorable conditions (warm water, high host density).

Impact and diagnosis: Infestations cause visible irritation, rubbing, flashing, and lethargy; heavy infestations can lead to secondary infections and reduced growth. Lice may be observed on the body, fins, or gills of fish. Diagnosis is typically based on visual inspection of the fish and, if needed, examination of gills.

Management: Quarantine of new fish, thorough cleaning of equipment and tanks, and treatment with approved parasiticides or medicated baths under veterinary guidance. Environmental management and reducing stocking density help prevent outbreaks.