Microsatellite flanking regions are often highly conserved in fish taxa, enabling their application in other species within or outside the source family. Moderately variable microsatellite markers may also be good candidates for species identification using multi-locus genotypes. We evaluated the degree of conservation of microsatellite flanking regions and the level of polymorphism in 4 commercially important eel species (Anguilla anguilla, A. rostrata, A. japonica and A. marmorata). Using multiplex polymerase chain reactions developed for the first 2 taxa, we assessed the discrimination power of an individual-based assignment method to differentiate all 4 species without initial species information. Detection and classification of each species was performed with high confidence (> 90%), as was assignment of randomly sampled individuals to pre-defined species (> 95%). Our results demonstrate the highly conserved nature of microsatellites and their level of polymorphism in Anguilla species. Although an inverse relationship was found between genetic diversity and differentiation estimates, likely due to homoplasy, assignment proved to be superior to multivariate and distance-based approaches for identifying the 4 species. The method enables the rapid screening of morphologically similar eel species using only 4 co-dominant nuclear loci and the detection of natural hybridisation or anthropogenic mixing between internationally highly traded species.
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