The salmon louse is an ectoparasite that forages on host mucus, skin, and blood, causing lesions and wounds that result in behavioural and transcriptomic responses; stress; osmotic imbalances; and secondary infections. The adverse effects of the parasite varies depending on infestation intensity as well as on the developmental stage of the lice, with a sharp increase in virulence when the lice moults from immobile chalimus II to mobile preadults (Grimnes and Jakobsen, 1996).There is intense focus on salmon lice, owing both to its severe impact, if left unchecked, upon the welfare of farmed salmon and to the concern that transmission from farmed salmon adversely impacts wild salmon. The salmon louse is considered among the most critical challenges to wild salmonids and salmon aquaculture in the North Atlantic, although controversies remain.