Microsatellite-based genetic diversity and admixture history of rainbow trout (Oncorhynchus mykiss – Walbaum, 1792) stocks in Trentino (Italy)

Italy is the first producer of rainbow trout in Europe (EU member) and Trentino farmers represent roughly 8% of this production, but genetic information of the stocks employed is still lacking. This study aimed to estimate the genetic variability of the rainbow trout stocks farmed in Trentino and to reconstruct the related admixture history. Sixty hundred and thirty-two animals belonging to 23 different stocks were analysed using microsatellite loci. Seventeen stocks showed negative values of inbreeding coefficient within population (Fis ranging from -0.06 to -0.107). NJ tree of genetic distances among stocks showed distinct clusters reflecting, at least partially, the information coming from known history. Discriminant analysis of principal components evidenced only 2 main groups of trout whereas model-based cluster analyses could detect 7 genetically distinct groups, underlining an influence from an old commercial Danish stock. Rainbow trout in Trentino showed a recent history of admixture with a lower level of genetic differentiation among stocks when compared to wild populations (FST = 7.7%). The results confirmed the rather similar genetic origin of the analysed populations, highlighting the necessity to carefully manage the stocks to prevent phenomena of inbreeding and, more often, outbreeding depression.