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Sea lice are from fish-farms

Research published in Nature suggests that lice found in wild salmon populations originated in the farmed salmon environment. The parasitic salmon louse and its resistance to delousing agents represents one of the greatest challenges to the salmon farming industry. Researchers in Norway identified a gene in the salmon louse that was resistant to the organophosphates farmers use to kill lice and that was selected for in lice found on salmon in an aquaculture environment.

The resistant allele of this gene was found in lice on wild sea trout and salmon, and in greater frequencies in wild fish that were closest to salmon farms. Wild fish would not be expected to carry this allele of the gene. This suggests that there is an extensive exchange of lice between wild and farmed hosts, and indicates that in farming-dense regions of Norway, aquaculture represents a major driver of salmon louse population structure.

It was also noted that in most regions, the frequency of the resistant allele was higher in lice collected from wild sea trout than wild Atlantic salmon, but in all regions was similar.

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