Same Fishways, Different Rivers: Do Ecohydrological Origins Shape Passage Strategies in Allopatric Mediterranean Cyprinids?

River fragmentation caused by dam construction threatens global fish conservation. Mediterranean ecosystems are particularly affected, and the Iberian Peninsula, with its highly fragmented rivers, exemplifies this challenge. Endemic allopatric congeneric barbels ( Luciobarbus bocagei and L. sclateri ) are particularly vulnerable cyprinids because they rely on river connectivity for migration. Despite the deployment of fishways, their effectiveness in Mediterranean rivers with variable hydrology and high endemism remains unclear. This study compares the passage of L. bocagei (Duero basin) and L. sclateri (Segura basin) across two fishway types: Vertical Slot and Submerged Notch with Bottom Orifice. Passage trials were analysed using standardised metrics, motivation, ascent success, and transit time, under a time-to-event framework. Results suggest that species, size, ecohydrological context, and fishway interact to shape passage outcomes. L. sclateri exhibited higher motivation and faster passage attempts, likely reflecting adaptation to ephemeral flows. Ascent success was similar between species and fishway type. Larger individuals demonstrated greater motivation and shorter transit times, regardless of species or fishway. These findings highlight the importance of integrating ecohydrological context and behavioural variability into fishway assessment. Adaptive management accounting for species- and site-specific traits is essential to enhance connectivity and support endemic populations under growing anthropogenic and climatic pressures.