Spatial variability in streamflow characteristics is responsible for a large range of habitat variations to which fish are adapted through life-cycle strategies and morphological adaptations. In this study, we compared the swimming performance and related morphology of two Iberian barbel populations from permanent and temporary rivers. The permanent river was characterised by its Atlantic influence with higher water availability and a more unstable and turbulent environment, contrasting with the lower discharge setting observed in the southern Mediterranean ecosystem during most of the hydrological year. Barbels from the permanent river exhibited a higher critical swimming speed (U crit ) associated with a more fusiform body shape, narrower head and caudal peduncle, lower body condition and longer and higher pectoral and dorsal fins, when compared with the population from the temporary watercourse. These results reflect a morphological response in a way to reduce hydrodynamic resistance and energy expenditure during locomotion that we hypothesise here to be related with the different hydrological regimes of the studied systems.

Decline in fish species populations due to river regulation by dams and weirs promoted the development of fishways, which are becoming one of the most common measures for the restoration of connectivity in rivers. Fishways efficiency can be species specific and thus monitoring and evaluation, and subsequent adjustments to design and hydraulic features, are required to inform potential users prior to installation. In this study we tested the applicability of electromyogram telemetry to study the swimming behavior of a cyprinid potamodromous species, the Iberian barbel Luciobarbus bocagei Steindachner, 1864, in an experimental pool-type fishway. In total, 24 barbels were used in the experiment, 12 of which were tagged with EMG radio transmitters equipped with electrodes that register muscle activity, while the other 12 untagged fish were used as control. For tagged fish, a relationship between swimming speed and EMG telemetry signals was developed in a swimming tunnel, which was later used to assess barbels swimming behavior within the experimental fishway. Tagged fish exhibited high passage success and anaerobic burst swimming was only required to move through the submerged orifices of the fishway. Barbels spent successively less time when transversing the pools in the upstream direction. Measured hydraulic variables that were related with barbels' swimming speed within the fishways were the water velocity, turbulent kinetic energy, turbulence intensity and, especially, the horizontal component of Reynolds shear stress, highlighting the importance of these parameters when designing pool-type fishways.

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The main purpose of this study was to gather swimming performance information for two endemic cyprinids of the Iberian Peninsula to contribute to the optimization of fish ways. Critical swimming speed (U crit ) was determined for the Tagus nase Pseudochondrostoma polylepis (Steindachner, 1864) and for the bordallo Squalius carolitertii (Doadrio, 1988) in a swimming tunnel. From a total of 80 P. polylepis tested, the mean (± SD) U crit observed was 0.78 ± 0.15 ms )1 (c. 3.74 ± 0.93 BL s )1 ); the 68 S. carolitertii tested presented an U crit of 0.54 ± 0.1 ms )1 (c. 4.43 ± 0.74 BL s )1 ). Significant interspecific differences were found between the U crit of the tested cyprinids. Intraspecific comparisons between the U crit and the variables of size, sex, condition factor and gonado-somatic index were also made. No sex-or gonad maturation-related differences between the U crit were identified, but the robust P. polylepis were found to be stronger swimmers. Water velocities in fish ways for P. polylepis and S. carolitertii should aim, on average, for lower than 0.7 and 0.5 ms )1 , respectively.

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