Genetic diversity of domestic brown trout stocks in Europe

Brown trout (Salmo trutta) is composed of numerous geographical forms in the wild and a multitude of stocks reared in hatcheries. Practices impacting this species are domestication and fish farming. Thousands of hatcheries are producing domestic trout which are frequently released in the wild without real knowledge of the origin and genetic composition of the strains and of the receiving populations. The present study contains an analysis of the genetic structure (using twelve microsatellites) of 26 hatchery strains from Europe (Sweden, Poland, Czech Republic, Slovakia, Hungary, France, Italy and Spain) and one from North America (Minnesota). Several new observations improved our knowledge on this domestic part of S. trutta. First, a cross-border commercial strain of the North Atlantic lineage occupies most of European hatcheries and the American one, as a probable consequence of intensive exchanges of broodstock materials over time. In addition to the common Europe-wide commercial Atlantic strain, local strains stemming from domesticated regional wild fish also occur. Second, the level of genetic polymorphism of most hatchery strains is high to very high, likely reflecting genetic admixture counteracting expected losses of diversity through random genetic drift and domestication. This study emphasizes the value of identifying the genetic composition of hatchery stocks used for releases. It further stresses the need for caution when stocking a common stock across the whole geographical range of a species, with risks for reducing the intraspecific genetic diversity and local adaptation.

Automated summary

This study analyzed the genetic structure of 27 brown trout hatchery strains from Europe and North America, revealing the dominance of the North Atlantic lineage in European and American hatcheries, with the presence of local strains from domesticated regional wild fish. Most hatchery strains showed high to very high genetic polymorphism, likely due to genetic admixture counteracting losses of diversity from genetic drift and domestication. This study highlights the importance of identifying the genetic composition of hatchery stocks and the need for caution when stocking a common stock across a species' geographical range to avoid reducing genetic diversity and local adaptation.