Microsatellites as a good approach for detecting triploidy in brown trout hatchery stocks

Abstract

Mediterranean brown trout (Salmo trutta) populations have been extensively supplemented with genetically divergent hatchery stocks to enhance recreational fishing, and the displacements of native gene pools are well documented. Because of the great difficulty to breed local stocks of native Mediterranean brown trout in the farm, the introduction of Atlantic sterile individuals such as triploids has been proposed as an alternative to the traditional exogenous stocks. Several protocols of optimization and production of triploid fish have been described in S. trutta, nonetheless triploidy is not always induced in the totality of individuals. Therefore, a cost-effective and rapid method is necessary for triploidy verification. Several methods have been used to confirm triploidy, many of them costly in time and effort, and some providing approximate results. Here, we validated highly polymorphic DNA markers –microsatellites– as a rapid, useful and easy tool to detect triploidy. A total of 16 putative triploids, induced by a shock-heat treatment that suppressed the formation of the second polar body, were genotyped with nine microsatellites. All but two individuals showed a pattern of three peaks that corresponded to three alleles at least at one locus, and thus were confirmed as triploids. Genotypes of the two remaining individuals fit on a diploid genome. Our results provide useful insights into the development of alternative methods to assess triploidy in brown trout. Because a large number of microsatellites have been described for many species the use of these highly polymorphic markers to detect triploidy is a valuable tool to be applied in hatcheries.