Delimiting Andean catfish species of the families Astroblepidae and Loricariidae (Ostariophysi, Siluriformes) in the Peruvian Andes using DNA barcodes.

The Amazon Basin, the largest on Earth, hosts an exceptionally rich fish fauna shaped by its ancient evolutionary history, vast environmental heterogeneity, and steep altitudinal gradient. Despite this diversity, major taxonomic gaps persist, including the Linnean shortfall-the large number of undescribed species-and the Wallacean shortfall, reflecting limited knowledge of species distributions. During the past two decades, DNA barcoding using the mitochondrial COI gene has helped uncover substantial cryptic diversity in Amazonian fishes, particularly along the Andean slope, where Siluriformes exhibit striking levels of undocumented diversity. In this study, we investigated catfish communities from the families Astroblepidae and Loricariidae in the headwaters of the Madre de Dios and Huallaga rivers in Peru, spanning elevations from 500 to 2,500 m. Using DNA barcoding and multiple species-delimitation methods, we identified 27 MOTUs, most of which could not be assigned to recognized species. Our aim was to examine diversity patterns, species co-occurrence, and phylogenetic community structure along the Andean slope. This framework allows us to evaluate how ecological processes-such as competition, niche partitioning, and ecological specialization-shape community assembly. Combined with evidence of close phylogenetic relationships among MOTUs, our results highlight the likely importance of in situ diversification in driving species turnover and structuring catfish biodiversity across Andean elevational gradients.