Admixture analysis and stocking impact assessment in brown trout (Salmo trutta), estimated with incomplete baseline data

Studies of genetic interactions between wild and domesticated fish are ofte n hampered by unavailability of samples from wild populations prior to popu lation admixture. We assessed the utility of a new Bayesian method, which c an estimate individual admixture coefficients even with data missing from t he populations contributing to admixture. We applied the method to analyse the genetic contribution of domesticated brown trout (Salmo trutta) in samp les of anadromous trout from two stocked populations with no genetic data a vailable before stocking. Further, we estimated population level admixture proportions by the mean of individual admixture coefficients. This method p roved more informative than a multidimensional scaling analysis of individu al-based genetic distances and assignment tests. The results showed almost complete absence of stocked, domesticated trout in samples of trout from th e rivers. Consequently, stocking had little effect on improving fisheries. In one population, the genetic contribution by domesticated trout was small , whereas in the other population, some genetic impact was suggested. Admix ture in this sample of anadromous trout despite absence of stocked domestic ated trout could be because of introgression by domesticated trout adopting a resident life history.