Erosion of the native genetic resources of brown trout in Spain

We analyzed the introduction of hatchery-reared trout in the Riutort Creek, a small stream in the eastern Spanish Pyrennees. We used gene correlation matrices between individuals to analyze the fish coancestry in the Riutort Creek samples and in the hatchery stock. Hatchery fish disturbed the single ancestry in the native population of the creek, and were clearly detected with principal coordinate analysis of the gene correlation matrix. The amou nt of introgression produced by successful introductions was estimated from the principal coordinate analysis projections of the matrix of F-ST values between the putative native Riutort Creek population, the hatchery stock a nd the introgressed population. In only two years the amount of introgressi on rose to 10%, indicating that 5% of the native ancestry is lost each year as a result of the stocking program. Based on these results, we review the present understandings on the genetic impact of hatchery fish on indigenou s Spanish brown trout populations. The stocking of these populations involv es a non-native broodstock widespread through the Spanish hatcheries, but s uccessful stockings appear to be limited to wild populations subjected to o ccasional releases in protected or unfished areas. Surprisingly, extensive stocking in fished areas result in a more limited genetic impact on the rec ipient native population.