Atlantic salmon is an important food species and increased production has been a main goal for Atlantic salmon aquaculture. Although conventional selection for rapid growth has successfully increased production rates, biotechnological approaches such as transgenesis have been employed to further enhance production in salmon and other species. The main focus of transgenic research for aquaculture has been to introduce genetic material coding for growth hormone (GH) genes, which have been found to increase growth rate, and in some cases fi nal size, several fold in various species (Nam et al. 2008), including salmon species (Du et al. 1992; Devlin et al. 1995). The closest such fi sh to commercialization is the “AquAdvantage” fi sh, an Atlantic salmon transgenic for a Chinook salmon GH gene fused to an ocean pout anti-freeze protein promoter (DFO 2013). While altered traits may be useful in aquaculture, there are concerns that phenotypic changes in fi sh due to the novel genetic material may have negative consequences on wild populations of the species and/or aquatic ecosystems (Devlin et al. 2006; Kapuscinski et al. 2007). Currently, there is limited data on the

1 Department of Ecology and Genetics/Animal Ecology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden.