Susceptibility of farmed and two origins of wild Atlantic salmon (Salmo salar) to experimental infestations with sea lice (Lepeophtheirus salmonis)

Abstract Atlantic salmon ( Salmo salar ) from two genetically distinct wild populations in Newfoundland and Labrador (Conne River, Garnish River) and the farmed population utilized in the province, were exposed to sea lice ( Lepeophtheirus salmonis ) copepodids in a common garden experiment. Conne River salmon had greater lice density compared to farmed fish irrespective of surface area and fin condition (farmed fish demonstrated greater fin erosion and surface area than wild populations), suggesting that additional factors (e.g., genetic influences) impacted the likelihood of lice infestations. Differences in lice locations were identified among salmon populations, particularly: 1) more lice on gills of farmed fish compared to Conne River salmon possibly due to differences in gill vascularization and localized immune responses; 2) more lice on paired fins of wild populations (significant only in Garnish fish) compared to farmed fish linked to a greater fin surface area in wild salmon due to higher erosion in farmed smolts.