Genetic and Microchemical Analysis of Population Structure in a Migratory Neotropical Fish

Anthropogenic environmental changes, including overfishing, hydrologic alteration, and habitat degradation, pose substantial threats to riverine fish populations and their migration routes.  Neotropical rivers contain a diverse assemblage of economically important migratory fishes, but relatively little is known about their population biology compared to North American species.  We examined dispersal and gene flow among six populations of Prochilodus mariae, a migratory fish species found in Venezuelan rivers with congeners distributed throughout South America.  Prochilodus species are very abundant, comprise key regional fisheries, and are important drivers of ecosystem processes.  By coupling biogeochemical otolith and microsatellite genetic techniques, we were able to evaluate both ontogenetic migration patterns of individual fish and population genetic structure on a regional level.

Chemical signatures of otolith cores indicate that there is site structure in four of the six populations: 75-85% of individuals from each of those rivers share a chemically distinct natal site.  We genotyped the same individuals using 11 polymorphic microsatellite loci to determine whether the site structure observed using chemical markers was sufficient to create genetic differences among populations.  We detected no population genetic structure, indicating that there is sufficient gene flow among the sampled populations for them to consist of only one genetic group.  Our results have important implications for the conservation and management of Prochilodus fisheries.  Management efforts based only on genetic data might focus on a region as a single unit, but the site structure observed in our chemical data indicates that single-river populations should be considered individually.  In accordance with studies in other systems, genetic and biogeochemical markers provide complementary information about Prochilodus population structure to ensure that fisheries management is conducted on an appropriate spatial scale.