The Phe362Tyr mutation conveying resistance to organophosphates occurs in high frequencies in salmon lice collected from wild salmon and trout
Fjørtoft, Helene Børretzen; Besnier, Francois; Stene, Anne; Nilsen, Frank; Bjørn, Pål Arne; Tveten, Ann-Kristin; Finstad, Bengt; Aspehaug, Vidar; Glover, Kevin
Journal article, Peer reviewed
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Date
2017Metadata
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Abstract
The parasitic salmon louse, and its resistance to chemical delousing agents, represents one of the
largest challenges to the salmon aquaculture industry. We genotyped lice sampled from wild salmon
and sea trout throughout Norway with the recently identified Phe362Tyr mutation that conveys
resistance to organophosphates. These results were compared to data from lice sampled on farmed
salmon in the same regions. The resistant (R) allele was observed in salmon lice from wild salmon and
sea trout throughout Norway, although its frequency was highest in farming-intense regions. In most
regions, the frequency of the R allele was higher in lice collected from wild sea trout than wild Atlantic
salmon, and in all regions, the frequency of the R allele was similar in lice collected from wild sea trout
and farmed Atlantic salmon. The R allele is only selected for in fish-farms where organophosphates are
used for delousing. Therefore, our results suggest extensive exchange of lice between farmed and wild
hosts, and indicate that in farming-dense regions in Norway, aquaculture represents a major driver of
salmon louse population structure. Finally, these data suggest that the wild hosts within the regions
studied will not delay the spread of resistance when organophosphates are used.