Abstract
The impact of escapees from aquaculture is of general concern for the sustainability of natural resources. Turbot Scophthalmus maximus is a marine flatfish of great commercial value whose land-based aquaculture started approx. 40 yr ago; hence, a low impact of escapees is expected on wild populations. However, enhancement of wild stocks using farmed turbot has been carried out along the Northeast Atlantic coasts in the last decades. Recently, a broad panel of single nucleotide polymorphism (SNP) markers (755 SNPs; 1 SNP Mb -1 ) has been used to evaluate the genetic structure of turbot throughout its distribution range, constituting the baseline to evaluate the impact of farmed fish in the wild. Two distinct origins were identified for farmed turbot (F _ORI1 and F _ORI2 ; F ST = 0.049), which differentiated from wild populations after 5 generations of selection (average F ST = 0.059), and consistent evidence of adaptation to domestication was de - tected. A notable proportion of fish of farmed ancestry was detected in the wild (15.5%), mainly in the North Sea, where restocking activities have taken place, determining genetic introgression in wild populations. Conversely, effects of land-based aquaculture appear negligible. A simulation exercise supported panels of 40 and 80 SNPs to identify fishes of F _ORI1 and F _ORI2 ancestry in the wild, respectively. Application to empirical data showed an assignment success (wild/farmed ancestry) of approx. 95% in comparison with the full SNP dataset. The SNP tools will be useful to monitor turbot of farmed ancestry in the wild, which might represent a risk, considering the lower fitness of farmed individuals.
Highlights
Seafood has become one of the most important sources of protein for human consumption (Danancher & Garcia-Vazquez 2011)
Wild samples showed higher diversity than farmed ones, the difference was more pronounced for the mean number
Evaluating the presence of farmed individuals and their impact on wild populations is a primary issue for developing a sustainable aquaculture industry and for providing guidelines for fisheries management
Summary
Seafood has become one of the most important sources of protein for human consumption (Danancher & Garcia-Vazquez 2011). Despite the advantage of providing an alternative source of animal protein, negative environmental outcomes, such as land use for feed production (Froehlich et al 2018) and the escape of domesticated fish. Genetic variability is distributed within and among populations in response to demographic and historical factors and to environmental adaptation throughout the natural range (Nielsen et al 2009). Impact has been evaluated especially for the most important domesticated salmonid species (Arias et al 1995, Toledo-Guedes et al 2014, Taranger et al 2015, Araguas et al 2017, Glover et al 2017). Impact evaluation of all farmed species is crucial for the management of aquaculture considering the ongoing expansion and the difficulty of predicting the ecological and genetic outcomes of escapees
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