Multi-species assessment of fish passage success and behaviour in a Larinier super-active baffle fishway

River fragmentation caused by low-head barriers represents a threat to longitudinal connectivity in freshwater ecosystems. Technical fishways are implemented to mitigate these impacts, yet their effectiveness for small-bodied non-salmonid species remains understudied under demanding hydraulic conditions. In this study, we evaluated fish passage performance in a Larinier super-active baffle fishway operating at a 15% slope, corresponding to the upper limit of recommended design criteria. Using PIT telemetry, we quantified upstream passage success, passage rate, and transit time for five non-salmonid species inhabiting the upper Tanaro River (NW Italy). Passage success was species-specific, ranging from 56.8% in Italian chub (Squalius squalus)to 47.0% in barbel (Barbus spp.), while Italian riffle dace (Telestes muticellus), European bullhead (Cottus gobio), and minnow (Phoxinus sp.) exhibited no upstream passage. Within species, body size emerged as a key driver of passage success, with a positive effect of larger body size on upstream passage rate. Transit time differed between species, with Italian chub traversing the fishway rapidly and barbel exhibiting prolonged and variable ascent times, reflecting contrasting behavioral strategies. Our results indicate that 15% slope Larinier fishways impose hydraulic selectivity and may disproportionately limit passage for small-bodied species, highlighting the need for species-specific considerations when designing fishways.