DNA barcoding reveals blend of silver catfish Rhamdia species from fish farms in Southern Brazil

Rhamdia quelen is the most produced native freshwater fish in fish farms in South Brazil. Until recently, Rhamdia branneri and Rhamdia voulezi were synonyms of R. quelen, and all the species are commercialized as silver catfish (locally called jundiá or bagre sapo) by the aquaculture industry. In fact, because these species are morphologically very similar, interspecific crosses easily might occur in fish farming. We employed standard DNA barcoding to identify jundiá molecular operational taxonomic units (MOTUs) in fish cultivated and commercialized in the industry and in possible escapees in the natural environment in southern Brazil. We analysed 48 individuals from six fish farms and 48 individuals from three rivers (Uruguay, Benedito Novo and Itapocu Rivers) using the mitochondrial cytochrome oxidase subunit I (COI). Four MOTUs were identified based on the estimated optimum threshold (OT = 0.77), and these MOTUs were concordant with Bayesian Inferece (BI) and Neighbour‐Joining (NJ) trees. Our results support the existence of at least three species in our dataset: R. branneri, R. voulezi, and R. quelen 1 and R. quelen 2. The interspecific genetic divergence ranged from 1.1% to 5.1% (mean = 3.5%), and the intraspecific distance ranged from 0% to 1.4% (mean = 0.24%). The presence of cultivated fish in the Uruguay and Benedito Novo Rivers provides evidence of genetic contamination in native populations. These results show the need to regulate aquaculture activities and to characterize the species and commercial lineages of silver catfish that are cultivated in South Brazil.