INTEGRATIVE TAXONOMY OF A NEW SPECIES OF HOPLIAS GILL (CHARACIFORMES: ERYTHRINIDAE) FROM THE UPPER PARANÁ RIVER BASIN, BRAZIL

Hoplias Gill has long been considered taxonomically challenging among Neotropical freshwater fishes, particularly due to the presence of cryptic species within the H. malabaricus complex, which exhibits extensive morphological overlap among lineages of many Neotropical drainages. In this study, an integrative approach combining morphological and molecular data was employed to describe a new taxon from the upper Paraná River basin, Brazil. A total of 22 specimens were analyzed using morphometric and meristic assessments, along with mitochondrial COI gene sequencing. Species delimitation was performed through multiple methods, including genetic distance analysis on the BOLD Systems platform, Automatic Partitioning (ASAP), Generalized Mixed Yule Coalescent (GMYC), and Poisson Tree Processes (PTP). Phylogenetic trees were reconstructed using Bayesian inference. Hoplias sp. n. presents distinct diagnostic characters among congeners: 36–37 perforated lateral-line scales (vs. 37–43), 13–15 predorsal scales (vs. 15–19), 37–38 total vertebrae (vs. 39–45), and a rectilinear arrangement of scales at the base of the caudal fin. Molecularly, it forms a distinct clade with minimum K2P genetic distances of 3.7% from its closest relative (H. auri), exceeding the commonly accepted 2–3% threshold for species delimitation. All applied methods consistently recovered the new taxon as an independent evolutionary unit: ASAP (nine groups; p = 8.79×10⁻³), GMYC (nine entities; p = 0.0007), and PTP (support = 0.999). The convergence of morphological and molecular evidence strongly supports the recognition of Hoplias sp. n. as a valid new species for the upper Paraná River basin. These findings enhance our understanding of the genus diversity and underscore the power of integrative taxonomy in resolving cryptic species complexes among Neotropical fishes, thereby helping to reduce the Linnean shortfall.