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-Passage performance of brown trout (Salmo trutta), Iberian barbel (Luciobarbus bocagei), and northern straight-mouth nase (Pseudochondrostoma duriense) was investigated in a vertical slot fishway in the Porma River (Duero River basin, Spain) using PIT telemetry. We analysed the effects of different fishway discharges on motivation and passage success. Both cyprinid species ascended the fishway easily, performing better than the trout despite their theoretically weaker swimming performance. Fishway discharge affected fish motivation although it did not clearly influence passage success. Observed results can guide design and operation criteria of vertical slot fishways for native Iberian fish. Key-words:Iberian fish / vertical slot fishway / fish passage / motivation / transit time Résumé -Aptitude au passage de la truite, Salmo trutta, et de deux cyprinidés ibériques, le barbeau ibérique, Luciobarbus bocagei, et le nase à bouche droite, Pseudochondrostoma duriense dans une passe à poissons à fentes verticales. La performance de passage de la truite (Salmo trutta), du barbeau ibérique (Luciobarbus bocagei), et du nase à bouche droite (Pseudochondrostoma duriense) a été étudiée dans une passe à fentes verticales dans la rivière Porma (bassin de la rivière Douro, Espagne) en utilisant la technologie PIT. Nous avons analysé les effets de différents débits dans la passe à poissons sur la motivation et la réussite de passage. Les deux espèces de cyprinidés montaient la passe facilement, étaient plus performantes que les truites, malgré leur performance de nage théoriquement plus faible. Le débit dans la passe affectait la motivation des poissons bien qu'il n'ait pas influencé clairement le succès de passage. Les résultats observés peuvent guider dans les critères de conception de passes à fentes verticales pour les poissons indigènes.

Many fish passes have been built across the world in recent years. This study analyses the performance of a modified type of pool and weir fishway with two access branches, using passive integrated transponder telemetry. A circum-Mediterranean barbel, Luciobarbus bocagei (Steindachner, 1864), was chosen as the target species. Both hydraulic values (flow and volumetric energy dissipation) and biological parameters (attraction, entrance and passage success) were measured in the fishway, these being related to the environmental variables affecting upstream fish movement. Flow discharge, water temperature and atmospheric pressure were important for fish entering the fishway. There was no preference between path routes, even though the main discharge was concentrated in the turbine channel. This type of fishway design could be an alternative for the conservation of fish populations where multiple fish approach options are possible. K E Y W O R D Sbarbel, competing risk, fish ladder, passive integrated transponder telemetry, time-to-event, transit time

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Fish need to move upstream and downstream through rivers to complete their life cycles. Despite the fact that fishways are the most commonly applied solution to recover longitudinal connectivity, they are not considered viable for downstream migration. Therefore, alternative facilities are recommended to facilitate downstream migration. However, a few recent studies have disagreed with this general assumption, showing the potential for bidirectional movements. This study advances our understanding of the potential of fishways for downstream migration by studying their efficiency in a run-of-the-river hydropower plant in the Duero River (Spain). To achieve this, downstream movements of the Iberian barbel (n = 299) were monitored in a stepped fishway for two years with passive integrated transponder (PIT)-tag technology, considering the effect of fish origin and release zone. The results showed that 24.9% of barbels descended through the fishway, with the origin and release zone affecting the fishway location. In addition, downstream movements were observed throughout the whole year, except in winter. The study concludes that, under specific scenarios, fishways could act as safe alternative routes for downstream migration.