In the present study, the population genetic structure of the Pacific thread herring (Opisthonema libertate) was analyzed through mitochondrial DNA (mtDNA) control region sequences. Organisms were collected from June 2015 to July 2015 from four commercial landing sites (Bahia Magdalena, Guaymas and Mazatlan, Mexico, and Puntarenas, Costa Rica) and one artisanal sampling site (Puerto La Libertad, El Salvador). A total of 125 sequences were analyzed. High levels of haplotype (h = 0.990) and nucleotide (π = 0.030) diversity were found. Pairwise Φst comparisons indicated differences attributed mainly to the organisms from El Salvador. However, Bayesian inferences did not support the existence of different populations. The haplotype distribution between locations did not show a clear phylogeographic pattern. Mismatched distribution showed a unimodal pattern for the five sampled areas, indicative of sudden demographic expansion. These results were supported by Bayesian skyline plot. Our results do not support the hypothesis that the Pacific thread herring presents a population genetic structure. Future genetic comparisons should include a larger number of samples as well as more polymorphic molecular markers to further support our results.
Keywords: Genetic structure; demographic expansion; genetic diversity; mitochondrial DNA.