Preliminary evidence of the demographic history of <i>Xystreurys rasilis</i> (Pleuronectiformes: Paralichthyidae) in the southwestern Atlantic as inferred from mtDNA

Xystreuris rasilis (Jordan 1891) is a flounder species from the southwestern Atlantic, perticularly abundant in high-salinity waters of the Buenos Aires Coastal Ecosystem and San Matías Gulf. It primarily feeds on benthic invertebrates and utilizes local frontal systems as breeding and nursery grounds. Analysis of a 406 bp fragment of the mitochondrial control region revealed high haplotype (h = 0.994) and nucleotide (n = 0.022) diversities. Genetic divergence between Necochea and San Antonio Oeste was low and not significant, with 18 unique haplotypes and no evident phylogeographic structure. Demographic analyses indicated long-term population stability, with the most recent common ancestor estimated at approximately 148,000 years ago. Results do not provide evidence for the existence of two discrete genetic units. Nevertheless, it is possible that the species experienced historical isolation followed by secondary contact between different lineages of the flounder X. rasilis.