Branchiura

Branchiura is a small group of crustaceans commonly known as fish lice. They are ectoparasites that attach to the external surfaces of fish, including the skin, fins, and gills. Branchiurans occur in both freshwater and marine environments worldwide and can affect wild fish populations as well as those kept in captivity.

Taxonomy and anatomy: Branchiura is traditionally treated as a subclass within Crustacea and includes two living families, Argulidae and Dolopsidae. Adults are dorsoventrally flattened with a broad thorax bearing swimming appendages; the head bears specialized piercing mouthparts for feeding on blood and tissues. They are parasitic and rely on the host for nutrition.

Life cycle and ecology: Branchiurans reproduce sexually. Females lay eggs in gelatinous masses attached to submerged objects or, in some species, near the host. The eggs hatch into free-swimming naupliar stages and subsequent infective larvae that seek out a fish host. When attached, they feed on blood and tissue, causing irritation and surface lesions. Heavy infestations can stress fish and compromise growth or health, and they may act as vectors for other pathogens.

Ecological and economic relevance: Branchiurans are particularly important in aquaculture and ornamental fish keeping because infestations can spread rapidly in dense populations and are difficult to eradicate once established.

Management: Control measures include preventing introduction of infected fish, maintaining good water quality and biosecurity, manual removal of parasites, and the use of approved chemical or physical treatments under veterinary or aquaculture guidance. Regular monitoring helps limit outbreaks.