Fishways are key mitigation measures for restoring longitudinal connectivity at man-made obstacles in rivers, yet their ecological effectiveness is rarely assessed through continuous, non-invasive monitoring. Here we present the preliminary results from a video-based monitoring system installed on a fishway on the Po River (La Loggia dam, NW Italy), designed to automatically record videos of each passage event (passage date/time, direction, fish length, and species through automated video analysis) 24/7 over long-term periods. From winter 2025 to summer 2026, 13 fish species were detected, including eight non-native ones (six of which only recorded moving downstream). Preliminary data suggest temporal patterns in passage activity, with native rheophilic species beginning their activity earlier in the season. Barbel (Barbus spp.) and Italian chub (Squalius squalus) were the most frequently detected species, showing increased activity during early spring, with bidirectional movement (both upstream and downstream). Upstream passages of endangered species, including the Italian roach (Rutilus pigus) and hybrid population of marble trout (Salmo marmoratus) were recorded alongside invasive and ecologically problematic allochthonous species, underscoring the complexity of managing freshwater fish populations. Among the allochthonous species, wels catfish (Silurus glanis) and common carp (Cyprinus carpio) showed upstream passage activity starting in May.

Beyond evaluating fishways performance, these results highlight the broader potential of continuous video monitoring as a tool for providing reliable data on the fish population composition, and on each species passage timing and behavioural and social dynamics that are rarely captured by traditional sampling methods, while also minimizing the negative impacts associated with other monitoring approaches. Knowledge of species-specific behaviour and timing could, in the future, support the design of selective passage systems aimed at reducing the potential detrimental effects of invasive allochthonous species exploiting fishway infrastructure.