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Studies of genetic interactions between wild and domesticated fish are often hampered by unavailability of samples from wild populations prior to population admixture. We assessed the utility of a new Bayesian method, which can estimate individual admixture coefficients evenwith data missing from the populations contributing to admixture. Weapplied the method to analyse the genetic contribution of domesticated brown trout (Salmo trutta) in samples of anadromous trout from twostocked populations with no genetic data available before stocking. Further, we estimated population level admixture proportions by the mean of individual admixture coefficients. This method proved more informative than a multidimensional scaling analysis of individual-basedgenetic distances and assignment tests. The results showed almost complete absence of stocked, domesticated trout in samples of trout from the rivers. Consequently, stocking had little effect on improving fisheries. In one population, the genetic contribution by domesticatedtrout was small, whereas in the other population, some genetic impact was suggested. Admixture in this sample of anadromous trout despiteabsence of stocked domesticated trout could be because of introgression by domesticated trout adopting a resident life history. [ABSTRACT FROM AUTHOR]