Translocation and introduction of non-native organisms can have major impacts on local populations and ecosystems. Nevertheless, translocations are common practise in aquaculture. Each year, millions of wild caught wrasses are transported large distances to be used as cleaner fish for parasite control in marine salmon farms. Recently, it was documented that translocated cleaner fish are able to escape and reproduce with local wild populations. This is especially a challenge in Norway, which is the world's largest salmon producer. Here, a panel of 84 informative SNPs was developed in order to identify the extent and magnitude of non-local corkwing wrasse (Symphodus melops) escapes and admixed individuals in populations in western Norway. Applying this panel to almost 2000 individuals, escapees and hybrids were found to constitute up to 20 percent of the local population at the northern edge of the species' distribution. The introduction of southern genetic material at the northern edge of the species range has altered the local genetic composition, and could obstruct local adaptation and further range expansion. Surprisingly, in other parts of the species distribution where salmon farming is also common, few escapees and hybrids were found. Why hybridization seems to be common only in the north is discussed in the context of demographic and transportation history. However, the current lack of reporting makes it difficult to evaluate possible causes for why some aquaculture-dense areas have more escapees and hybrids than others. The results obtained in this study, and the high genomic divergence between the main export and import regions, puts the sustainability of mass-translocation of non-local wild wrasse in question, and suggest the revision of the current management regime.</p><p>Provided in this bioproject are the raw reads of the 2bRAD sequences used to select and develop the panel of SNPs.