Evaluation of three atlantic salmon strains for resistance to copepodid sea lice attachment

Authors: Pietrak, Michael; Delomas, Thomas; Lifgren, Demitri; Polinski, Mark

Submitted to: Fishes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2025
Publication Date: 7/8/2025
Citation: Pietrak, M.R., Delomas, T.A., Lifgren, D.L., Polinski, M.P. 2025. Evaluation of three atlantic salmon strains for resistance to copepodid sea lice attachment. Fishes. 10,7,334. https://doi.org/10.3390/fishes10070334.
DOI: https://doi.org/10.3390/fishes10070334

Interpretive Summary: Sea lice are a pest of the salmon farming industry costing farmers approximately 9% of their farm gate value. per year. Methods to mitigate sea lice infestations are therefore desirable. In this study, we aimed to identify if different strains of Atlantic salmon with varying long-term lice exposure histories had different resistance to lice attachment. We additionally sought to characterize lice distributions on fin, head and skin, and identify if attachment location influenced lice behavior. Although lice counts were highest on St. John River strain salmon with open ocean-run evolutionary history compared to Grand Lakes Stream strain with 200-year restricted ocean-run access or Sebago Lake strain salmon with ~11,000 year landlocked history, this effect was correlated with body size – lice density was similar between strains. Variance in lice cellular signaling (a proxy for behavior) was minimally affected by attachment location even though lice strongly preferred fin relative to head or body. Attached lice did have different signaling profiles on Grand Lakes Steam salmon relative to Sebago Lake or Saint John River strains. This study cumulatively identified a minimal host evolutionary component for sea lice attachment resistance, although lice behavior post-attachment appeared somewhat affected by strain. Non-uniform settlement distributions and challenge-specific variability in lice attachment were observed across populations.

Technical Abstract: Sea lice have been a persistent pest of the salmon farming industry for more than 50 years. In this study, we aimed to identify if different strains of Atlantic salmon with discrete long-term lice exposure histories had variable resistance to copepodid attachment and/or different attachment-specific transcriptome patterns. We additionally sought to characterize lice distributions on fin, head and skin, and identify if attachment location influenced transcriptomic profiles of lice. Although lice counts were highest on St. John River (SJR; open ocean-run) relative to Grand Lakes Stream (GLS; 200-year restricted ocean-run) or Sebago Lake (CAS; ~11,000 year landlocked) Atlantic salmon, this effect was correlated with body size – lice density was similar between strains. Skin and fin had expectedly different transcriptomic profiles; however, notable differences were not observed between salmon strains. Variance in lice transcriptomes was minimally affected by attachment location even though lice strongly preferred fin relative to head or body. Attached lice did have different transcriptomic profiles on GLS relative to CAS or SJR. This study cumulatively identified a minimal host evolutionary component for sea lice attachment resistance, although lice behavior post-attachment appeared somewhat affected by strain. Non-uniform settlement distributions and challenge-specific variability in lice attachment were observed across populations.