| Summary: | The genetic impact of farmed fish escaping aquaculture is a highly debated issue. However, non-target species, such as cleaner fish used to remove sea lice from farmed fish, are rarely considered. Here we report that wild corkwing wrasse (Symphodus melops), which are transported long distances to be used as cleaner fish in salmon farms, escape and hybridize with local populations. Recently, increasing numbers of corkwing wrasse have been reported in Flatanger in Norway, north of its described distribution range, an area heavily relying on import of cleaner fish from Skagerrak. Using genetic markers identified with 2bRAD sequencing, we show that, although the Flatanger population largely is a result of a northwards range expansion, there is also evidence of considerable gene flow from southern populations in Skagerrak and Kattegat. Out of 40 corkwing wrasses sampled in Flatanger, we discovered two individuals with clear southern genotypes, one first generation hybrid, and twelve potential second-generation hybrids. In summary, we provide evidence that corkwing wrasse escape from fish farms and hybridize with local populations at the leading edge of an ongoing range expansion. Although the magnitude and significance of escapees warrants further investigation, these results should be taken in consideration in the use of translocated cleaner fish. genepop_file_4357_SNPsText file (genepop input format) containing the genotypes used for population genomics analysis. The file contains the genotypes of 4357 polymorphic SNPs typed in 240 individuals with 2bRAD, 40 from each of the 6 population samples. The population codes are FKH=Flatanger, SMAU=Austevoll, SMID=Stavanger, SMTF=Kristiansand, SMST=Strömstad and SMKB=Kungsbacka.west_genepop4357ID.txtvcf_genotypes_4372_SNPsVCF file containing filtered polymorphic SNPs from 2bRAD sequencing. The file contains the genotypes of 4372 SNPs typed in 240 individuals, from 6 population samples. The population codes are FKH=Flatanger, SMAU=Austevoll, SMID=Stavanger, ...
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