The effect of sea lice on Atlantic Salmon and other salmonid species

Sea lice were historically observed in rather low numbers on wild salmonids, with few adverse effects on the host being reported. Since the late 1980s, however, there have been several reports of sea lice epizootics on salmonids in Norway, Scotland, Ireland, and more recently Canada. Infested post-smolts and adult fish often have been reported to be in poor physical condition, with some showing severely damaged caudal and dorsal fins and skin lesions. It has been suggested that the apparently increased infestation rate of sea lice on salmonids is correlated with the presence of salmon farms. This has been the focus of a long and controversial debate. Management improvements on fish farms have therefore aimed specifically at enhancing husbandry of cultured fish by reducing their infestations of sea lice. This approach has been taken with the additional objective of reducing their potential impact on wild salmonids. Here we give an overview of the differing experiences and responses of national bodies and the farming industry to the environmental challenges presented by sea lice in Norway, Canada, Ireland and Scotland. Whilst the emphasis is on the effect of sea lice on Atlantic salmon performance, some additional information on sea lice impacts on sea trout, Arctic charr and Pacific salmon is included.