New data about distribution of <i>Barbus</i> sp. in the Isonzo Basin, a buffer area between Po plain and Balkan species

Accurate and up-to-date information on the geographical distribution of fish species is crucial for effective management and conservation policies, especially for organisms of community interest that require careful protection. However, defining distribution areas can be challenging, especially in regions where the ranges of closely related species overlap. Moreover, taxonomic advancements may identify new species, while transfaunation can alter existing distribution patterns. This study presents new data on Barbus sp. in the Region Friuli Venezia Giulia (north-east Italy), a key area where typical Po-Plain fish species coexist with those of Balkan origin. Our findings, based on meristic and genetic analyses, confirm that Barbus balcanicus is present exclusively in the Isonzo River Basin, providing new data on its distribution within the studied hydrological network. Barbus plebejus is the only other Barbus species hosted in the studied area, while Barbus caninus was never observed, despite historical reports. This result strongly suggests that past records of B. caninus in Friuli Venezia Giulia – in the Isonzo River Basin – were misidentifications, as B. balcanicus was only recognized as a distinct species in recent times. As observed in other fish species, our study highlights the Isonzo River Basin’s role as a key biogeographical buffer zone, where Italian and Balkan overlap. Accurate species identification and distribution data are essential for implementing effective conservation strategies, particularly in biodiversity hotspots such as this cross-border region between Italy and Slovenia, where coordinated international efforts are crucial for species protection.