Global Aquaculture Alliance —
Atlantic salmon (Salmo salar) is reportedly the most economically important species in aquaculture globally. However, increased production has resulted in a larger number and stronger impact of diseases, with parasitic salmon lice becoming one of the most important in recent years in all the major salmon-producing countries.
Two lice species are of primary concern for salmon farming: Lepeophtheirus salmonis in the Northern Hemisphere and Caligus rogercresseyi in the Southern Hemisphere. In our study, we focused on the former species, L. salmonis, which predominates in the North Atlantic and causes year-round infestations of Atlantic salmon reared in marine cages, with associated consequences for fish health in both farmed and wild salmonids as well as for aquaculture economics and sustainability.
Sea lice parasitize salmon during the marine phase of the life cycle, in both wild and farmed salmon, by attaching to their skin, often close to gills and fins; feeding on the mucus, epithelial tissues and blood; reproducing on the host; and releasing the eggs into the seawater. If left untreated, this can lead to impaired growth, osmoregulatory stress and open wounds, which can facilitate the entry of other pathogens. The impaired growth and secondary infections cause significant negative animal welfare and economic impact. Moreover, relative to other salmonids, Atlantic salmon have limited ability to resist infection by L. salmonis and are therefore highly susceptible to the parasite.