Origin of Fish Biomass in a Diverse Subtropical River: An Allochthonic-Supported Biomass Increase Following Flood Pulses

Accumulation of human pharmaceuticals and activity of biotransformation enzymes in fish from two areas of the lower Rio de la Plata Basin

The accumulation of four human pharmaceuticals active compounds (HPhAC) in the muscle of four fish species of the Rio de la Plata Basin were assessed regarding the compound logP and pKa, and fish trophic levels. For Prochilodus lineatus, accumulation was compared to hepatic biotransformation enzymes and fish from two sampling areas with different urbanization degree. Species were the detritivore Prochilodus lineatus, the omnivores Megaleporinus obtusidens and Pimelodus maculatus, and the piscivorous Salminus brasiliensis. Sampling areas were the Inner Rio de la Plata Estuary (RLP), in front of the Buenos Aires Metropolitan Area, and at the Lower Uruguay River (URU), a relatively unpopulated area. Carbamazepine, atenolol, enalapril, and sildenafil concentrations in fish muscle were analyzed by HPLC-MS. EROD, BROD, and GST activities were measured in P. lineatus liver. Average (maximum) concentrations and detection frequency were: Atenolol 24.4 (69.4) μg kg^-1, 60%; carbamazepine 5.5 (45.8) μg kg^-1, 19%; enalapril 7.0 (56.9) μg kg^-1, 28%; sildenafil 17.1 (71.6) μg kg^-1, 56%. Enalapril and sildenafil detection in fish was first-time reported. Atenolol and carbamazepine concentrations were positively correlated. No correlation was observed between HPhAC accumulation and logP or pKa. A potential biomagnification trend was observed for atenolol, showing higher accumulation in S. brasiliensis. HPhACs accumulation was higher for P. lineatus collected at URU, but GST and BROD were significantly higher for individuals sampled at RLP and were positively correlated. A significant negative correlation was observed for enalapril and BROD. The study contributes to the knowledge of the accumulation of HPhACs in fish.

Diets and Trophic Structure of Fish Assemblages in a Large and Unexplored Subtropical River: The Uruguay River

The Neotropics represent a hotspot for freshwater biodiversity with vast number of fish species of scarce ecological knowledge. This hold true for the Uruguay River, where fish assemblages and their diets remain unexplored. Fish assemblages were surveyed in 14 sites along its main course, from headwaters to mouth (approximately 1800 km), with the aim to identify the trophic roles of fish and to describe trophic structure of these assemblages. Following standardized samplings, diet was determined to perform a trophic classification of species. One hundred species (2309 gut contents) were analysed and classified into four trophic groups subdivided into eight lower-level groups: Piscivore, piscivore-invertivore, detritivore, omnivore-detritivore, omnivore-invertivore, omnivore-planktivore and omnivore-herbivore. The trophic structure of the assemblages varied along the river, with the relative species richness of fish consuming terrestrial invertebrates increasing towards the middle river section, probably driven by the large floodplains in that areas, supporting global theories such as flood pulse concept. This study describes the feeding habits of fish along the Uruguay River, being the first dietary description for 29 species. This knowledge is essential for management and conservation, serving as baseline in the context of future environmental changes and generates novel evidence about the functioning of ecosystems in this scarcely studied climatic region.