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Longitudinal river fragmentation through physical barriers is a major issue for the conservation of aquatic species in regions with intense hydropower development, such as Chile. The construction of fishways is the main mitigation strategy for maintaining connectivity for fish but development of designs suitable for a broad range of species is challenging. Recent work has shown that two species native to Chile, Cheirodon galusdae and Basilichthys microlepidotus exhibited similar swimming performance in free flow in the laboratory, indicating that a single fishway design may be suitable for both species. However, in the complex, three-dimensional altered flows observed in fishways, swimming performance is likely to vary from the free flow case due to the adoption of distinctive swimming gaits, variation in swimming styles, and the potentially destabilizing effects of wake vortices. In order to improve criteria for hydraulic design of fishways for multiple species we study the behavior and tail beat kinematics of C. galusdae and B. microlepidotus (juveniles), in the wake of vertical and bottom-mounted cylinders in an open channel flow. Cheirodon galusdae swam using a burst-and-coast style. This species avoided the cylinder wakes, searching for more favorable flow conditions. Basilichthys microlepidotus adopted a Karman gait-like swimming strategy to swim in the cylinder wake. Tail beat frequency was constant in all experiments for both species, but in the presence of cylinders >2 cm in diameter, C. galusdae diminished the duration of the coast phase evidencing a higher propulsive effort. Tail beat amplitude of both species increased with the vortex length scale and decreased linearly with vortex shedding frequency. The fish Strouhal number correlated well with the relative vortex size and shedding frequency, compiling the swimming effort of species with very different behaviors, indicating that it is a suitable criterion for fishway design.

Connectivity plays a crucial role in maintaining the structural and functional attributes of river networks. Therefore, the loss of connectivity (fragmentation) alters the functioning and diversity patterns of the biota at local and regional scales. The global hydropower boom is one of the main drivers of river network fragmentation, with significant effects on the diversity of riverine biota. Analyses of beta diversity of fish assemblages in rivers with different degrees of fragmentation can give new insights into mechanisms that contribute to the responses of these assemblages to fragmentation. Here, fish beta diversity within six river networks of central Chile with different levels of fragmentation was studied to assess the responses of fish assemblages to fragmentation. A hypothesis of a significant effect of fragmentation on the beta diversity of native and non-native fish in riffles and pools was tested. This effect is expected to be modulated by both changes in environmental heterogeneity and direct obstruction of natural dispersal routes. Beta diversity based on variation of assemblage structure and environmental heterogeneity showed significant differences among river networks. Fish beta diversity showed a clear response to fragmentation in recently fragmented rivers. Specifically, the beta diversity of native fishes in pools and non-native fishes in riffles decreased with increase of the ratio between the longest non-fragmented sections of the river network to the total length of the network. These effects of fragmentation on fish assemblages were modulated by the biological features of each species, and open-water species were most severely affected. These results have significant implications for planning of the placement of new barriers in river networks subjected to hydropower boom. Planning of the placement of new barriers should consider the maintenance of long, connected sections within river networks in order to minimise the effects of fragmentation on fish biodiversity.

Percichthys trucha is a freshwater fish, endemic to southern South America and widely distributed in both, eastern and western sides of the Andes. P. trucha has been described as top native predator in lacustrine ecosystems, experimenting diet shifting during their life history development. Salmonid invasions have impacted their natural ecology through trophic niche interference and predation over alternative high quality prey. This study focuses on populations of P. trucha in western Patagonia, where its trophic ecology have been less understood. We hypothesised a diet shift between juveniles and adults from lower-trophic position prey towards higher-trophic position prey. Fish were collected from 7 lakes belonging to Puelo and Baker river basins, covering a high diversity of environmental conditions. Stomach content and δ15N stable isotope ratio of muscle tissues of 313 individuals were analysed. Results indicate significant differences in diet between juveniles and adults, shifting from planktonic/benthic preys towards benthic/piscivory, and concomitantly enrichment in heavier nitrogen isotope suggest trophic scaling. No trophic scaling was observed in populations inhabiting lakes with any other fish species present, essentially due to lack of Galaxias sp. as available prey and absence of cannibalism. Despite the fact that P. trucha and Galaxias sp. co-occur in studied river basins, no salmonid-free lakes harbouring this two native species were found, making it difficult to elucidate exact effects of salmonids on trophic scaling of P. trucha. Consumption of aquatic Odonata nymphs, however, arises as one of potential key mechanism for resilience of native food webs to salmonid invasion.

Biotic homogenization in freshwater ecosystems is a growing concern among conservation biologists. Recent phylogeographic data has shown low genetic structure between some basins from Central Chile, suggesting that either current dispersal through irrigation canals or incomplete lineage sorting due to recent divergence might explain the observed patterns. However, these hypotheses remain untested despite their potential implications for freshwater biodiversity and conservation. We used a statistical, model-based framework (approximate Bayesian computation) to investigate the relative support for each of these hypotheses in the freshwater catfish Diplomystes cf. camposensis, an endangered species from Central Chile. Our results show strong support for the model involving current migration between basins, and rejected the model of recent divergence without migration. These results strongly suggest that irrigation canals are facilitating the dispersal between basins, posing a serious threat to biodiversity in Central Chile, an area considered a biodiversity hotspot. Finally, these results highlight the utility of model-based approaches for determining demographic processes with potential conservation implications, even with the lack of extensive molecular data.