Integrative morphometric and molecular analyses reveal possible genetic contamination of silver catfish populations of the genus Rhamdia in Neotropical River basins.

Rhamdia quelen, Rhamdia branneri and Rhamdia voulezi are morphologically similar species that, until recently, were considered synonymous. Although R. quelen has wide distribution in the Neotropical region, R. branneri and R. voulezi are sympatric and endemic species of the Iguaçu River basin. We used an integrative approach, including morphometric and molecular data (barcodes DNA, COI gene), to assist in the identification and delimitation of these species. We also intended to investigate genetic contamination of the Paraná III and lower Iguaçu River basins, as silver catfish production has increased in southern Brazil, and accidental or occasional escapes to nature may pose risks to the genetic integrity of native populations. COI sequences and morphometric data were efficient in the characterization and differentiation of Rhamdia species and may be helpful tools in correctly identifying R. quelen, R. branneri and R. voulezi. Both morphometric and molecular analyses indicated the segregation of specimens into three groups. Although this separation coincided with the taxonomy and the collection site in the morphometric analyses, the taxonomic identification of most samples did not coincide with the molecular identification. This fact may be due to (i) incorrect morphological identification and/or (ii) escapes of pure species and/or interspecific hybrids from fish farms. The detection of COI haplotypes of R. quelen in the lower Iguaçu River, as well as COI haplotypes of R. branneri and R. voulezi in the Paraná III basin, combined with the morphometric and morphological characteristics of the specimens, reinforces the occurrence of hybrid specimens in these river basins. These results reveal the importance of characterizing species and interspecific hybrids of Rhamdia and the urgency to regulate aquaculture activities.