Florencia Paola Coronel ¹ Gisela Loretán ² Sebastián Sanchez ³ Natalia Silva ³ Gualberto Pacheco-Sierra ⁴ Florencia Brancolini ⁵ Danilo Aichino ⁶ Facundo Vargas ⁷ Pablo Scarabotti ⁸ Carla Simone Pavanelli ⁹ Eva Carolina Rueda ^1*

• ¹ Laboratorio de Genética - Facultad de Humanidades y Ciencias, Universidad Nacional del Litoral, Santa Fe, Argentina
• ² National Institute of Limnology (INALI), Santa Fe, Santa Fe, Argentina
• ³ Universidad Nacional del Nordeste, Corrientes, Argentina
• ⁴ Mazatlan Academic Unit, Institute of Marine Sciences and Limnology, National Autonomous University of Mexico, Mazatlan, Mexico
• ⁵ National University of General San Martín, San Martín, Buenos Aires, Argentina
• ⁶ National University of Misiones, Posadas, Misiones, Argentina
• ⁷ Gobierno de Chaco, Resistencia, Argentina
• ⁸ Instituto Nacional de Limnología (CONICET-UNL), Santa Fe, Argentina
• ⁹ State University of Maringá, Maringá, Paraná, Brazil

Megaleporinus obtusidens (Valenciennes, 1837), also known as "boga", is a freshwater teleost fish species with an extensive distribution across South America and a significant commercial value in Argentina and Brazil. Fishers, especially in the lower Paraná River, often categorize the boga fish they catch as M. obtusidens. The taxonomic classification of the boga fish has been examined using a variety of approaches, including cytogenetics, molecular data, and morphological analysis. However, the determination of species within the genus Megaleporinus is still subject to intense debate among researchers, resulting in discrepancies in the literature. The aim of this study was to assess the diversity of specimens captured in the La Plata River Basin, which are initially classified as Megaleporinus obtusidens by fishers, using DNA barcoding. This tool provides reliable species identification and, in some cases, helps to discover hidden diversity. We applied the mitochondrial COI marker to explore species assignment and genetic diversity in Megaleporinus, one of the most commercially exploited genera, in the southern area of the La Plata Basin. Our findings indicate that some of the boga samples previously identified as M. obtusidens are M. piavussu. Additionally, our findings highlight significant differences in the geographic distribution, diversity and genetic structure between the species. These results underscore the need for studying the ecology of each species separately, with the aim to define proper resource management and therefore contribute to the conservation of ichthyofauna.