lakselus

Lakselus, commonly translated as salmon lice, are ectoparasitic copepods that infect salmonids, especially Atlantic salmon (Salmo salar) and rainbow trout. They occur in coastal and offshore aquaculture regions and in the wild along temperate coastlines. In Norwegian usage, lakselus refers to Lepeophtheirus salmonis and related sea lice species that feed on the skin of their hosts.

The life cycle is direct and has several stages. Free-swimming nauplius and copepodid larvae seek a host, then attach as chalimus or preadult lice before maturing into adults. Each gravid female lays egg strings that hatch into larvae, allowing transmission between hosts and locations. Environmental conditions such as temperature and salinity influence development and spread.

Infestation damages the host by feeding on skin, mucus, and tissue, causing lesions and osmoregulatory stress. This can reduce growth, increase energy expenditure, and raise mortality in crowded farms. Sea lice can also facilitate secondary infections and disease, and they pose concerns for wild salmon populations through spillover between farmed and native stocks.

Management rests on integrated control: regular monitoring, treatment thresholds, and a mix of approaches. Biocontrol uses cleaner fish such as lumpfish and wrasse to remove lice. Physical methods include freshwater or hydrogen peroxide baths, and chemical or pharmaceutical treatments are applied judiciously to limit resistance and environmental impact.

Governments and industry regulate lakselus through fish-health rules, reporting, and surveillance programs. Research continues into breeding for resistance, vaccines, and improved delousing technologies to reduce reliance on chemicals and limit ecological effects.