BackgroundBarbels are ray finned cyprinid fishes of the Old-World with partially unresolved, intricate taxonomy. Within the Barbus sensu lato paraphyletic assemblage, Barbus sensu stricto is a monophyletic tetraploid lineage of Europe, northern Africa and Middle East, including two monophyletic sibling genera: Barbus and Luciobarbus. Italy, Slovenia and northern Croatia are natively inhabited by several entities of the genus Barbus, whose relationships and taxonomic ranks are still unclear. Aim of the present work is to focus on phylogeography of Italian and Slovenian barbels, with an appraisal of their current taxonomy.ResultsOne hundred fifty specimens were collected in 78 sampling sites from 33 main watersheds, widely distributed along Italian and Slovenian ichthyogeographic districts. We amplified two mitochondrial markers, cytochrome b (cytb) and control region (D-loop), to infer a robust phylogeny for our sample and investigate on species delimitation.Our results strongly indicate all Italian and Adriatic Slovenian fluvio-lacustrine barbels to be comprised into at least three distinct species. We provide a proposal of taxonomic revision and a list of synonymies for two of them and a new description under the International Code of Zoological Nomenclature rules for the third one.ConclusionsIf nuclear data will confirm our findings, at least three specific entities should be acknowledged across our sampling area. Namely, the three species are (i) Barbus plebejus, in the Padano-Venetian district; (ii) Barbus tyberinus, in the Tuscany-Latium district; (iii) Barbus oscensis Rossi & Plazzi sp. nov., in the Tyrrhenian and southernmost-Adriatic parts of Apulia-Campania district. Finally, we briefly discuss the implications of such a taxonomic scenario on conservation policies.