Tracing Historical River Connectivity Through Freshwater Fish Assemblages: The Case of Göksu River and Lake Beyşehir

The present study documents the first records of Oxynoemacheilus angorae and Oxynoemacheilus eregliensis in the Göksu River within the Mediterranean basin, which points to historical connectivity between the Göksu River and Lake Beyşehir systems. Whereas O. angorae is mainly distributed in the Western Black Sea, Marmara and Lakes Region, O. eregliensis, previously restricted to the Beyşehir basin, Yeşildere region in Central Anatolia and the Manavgat drainage in southern Anatolia, was identified through morphological and molecular analyses (COI barcode), confirming their taxonomic status. A review of topographical data indicates that the headwaters of the Göksu River and the Lake Beyşehir basin are separated by only minor elevation differences, with no significant mountain or hill barriers, highlighting their close proximity. This observation provides evidence that some geological changes may have resulted in partial deflection of the water flow, allowing the dispersion of freshwater species across these systems, ultimately leading to their disjunct distribution. The occurrence of common fish species between them is also indicative of a link in the past and pinpoints the role of geomorphological processes on freshwater diversity.