Impact of origin (wild vs. farmed) and sea lice (Lepeophtheirus salmonis) infestation on expression of immune-relevant genes in Atlantic salmon (Salmo salar L.) skin

The parasitic copepod salmon louse (Lepeophtheirus salmonis) is cause of concern for Atlantic salmon (Salmo salar) aquaculture due to economic losses, ecological impacts and negative influence on public opinion. Sea lice could spread between farms and from farmed to wild salmon. It is fundamental to understand susceptibility to L. salmonis within wild and farmed populations, to manage possible wild-farmed interactions. Two distinct wild salmon populations from rivers adjacent to aquaculture operations (Garnish and Conne River, Newfoundland, Canada) and one farmed population were challenged with L. salmonis. Skin samples of non-infested, low-infested (≤ 7 lice) and high-infested salmon (≥17 lice) from each population were analyzed by qPCR for the expression of 20 immune-relevant genes. Wild and farmed infested salmon presented dose-responsive up-regulation of key immune-relevant genes (HAMP, CTL-A, LECT2). The wild populations showed a different basal skin transcript profile for CAMP2, IL8 (down-regulated), IgT, GAPDH, iNOS, and CD8a (up-regulated) compared to the farmed population. This may highlight a discrepancy in both innate and adaptive (local and systemic) immune system function between wild and farmed salmon.