Passage performance of two cyprinids with different ecological traits in a fishway with distinct vertical slot configurations

Adequately designed vertical slot fishways (VSF) mitigate the impact of anthropogenic obstructions on fish migrations. Until now, most studies on VSF were conducted focusing on high priority species, particularly salmonids, while other species, such as cyprinids, have received less attention. In Mediterranean rivers, where water availability is a problem, effective low discharge fishways are desirable. Attempting to contribute towards filling this gap, the present study focuses on the behaviour and passage performance of two Iberian cyprinids with different ecological traits, the Iberian barbel (Luciobarbus bocagei, Steindachner, 1864) and the Southern Iberian chub (Squalius pyrenaicus, Günther, 1868). Fish passage performance was investigated in a full-scale experimental VSF under two different slot configurations (C1 and C2), which require different discharges for equal mean water depths in the pools (Q = 110 L s−1, for C1, and Q = 81 L s−1, for C2). Results show that the chub, a small-bodied fish that utilises the upper portion of the water column, performed a higher number of upstream movements in C2, while for the barbel, a large-bodied potamodromous bottom-oriented fish, the performance was similar in both configurations. With similar overall passage success, slot configuration C2 requires a lower discharge to operate, making it the more cost-effective geometry, especially in regions affected by water scarcity.