Uso estuarial y composición de las especies de peces en el sub-estuario Solís Grande, Uruguay

A total of 1,298 fish representing estuarine, freshwater, marine migrants, anadromous and catadromous species were caught. Dominance of postlarvae and juveniles was observed. Mugil liza was the most abundant species. Jenynsia multidentata, Pogonias cromis and Cyprinus carpio were new records of species for the Solís Grande sub-estuary.Fueron capturados un total de 1.298 peces, representando especies estuariales, dulciacuícolas, marino migrantes, anádromas y catádromas. Fue observada una dominancia de post-larvas y juveniles. Mugil liza fue la especie más abundante. Jenynsia multidentata, Pogonias cromis y Cyprinus carpio fueron nuevos registros de especies en el subestuario Solís Grande

Diets and trophic structure of fish assemblages in a large and unexplored subtropical river: The Uruguay river

This article belongs to the Special Issue Trophic Interactions in Warm Freshwater EcosystemsThe Neotropics represent a hotspot for freshwater biodiversity with vast number of fish species of scarce ecological knowledge. This holds true for the Uruguay River, where fish assemblages and their diets remain unexplored. Fish assemblages were surveyed in 14 sites along the river main course, from headwaters to mouth (approximately 1800 km), with the aim to identify the trophic roles of fishes and to describe trophic structure of these assemblages, following standardized sampling campaigns and laboratory procedures. 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 the 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 while generating novel evidence on the functioning of ecosystems in this scarcely studied climatic region

Evaluating the role of predatory fish controlling the invasion of the Asian golden mussel Limnoperna fortunei in a subtropical river

The invasive Asian golden mussel Limnoperna fortunei is continuously expanding through South America, altering aquatic ecosystem structure and functioning. While several native fish species predate on this mussel, these interactions, and their consequences for the food web, have not been studied in depth. We combine a survey of the fish assemblage trophic structure using gut contents and stable isotope analysis with an in situ exclusion experiment in order to: (a) determine the main fish species predating on L. fortunei; (b) estimate the contribution of L. fortunei to the biomass of fish assemblage; and (c) evaluate the role of fish on the density and maximum shell length of L. fortunei in the lower Uruguay River (the Río de La Plata Basin). We found that about one third of fish species in the assemblage (28 out of 81 species) consumed L. fortunei, which was an important food item (>10% of the dietary volume and >30% of frequency of occurrence) for 11 fish species. Stable isotope mixing models consistently suggested that >14% of the total biomass of the fish assemblage was derived directly from carbon derived from L. fortunei tissues. In addition, the exclusion experiment demonstrated that fish predation reduces the mussel density by c. 70% and the mussel maximum shell length by c. 40%. Synthesis and applications. Our research suggests a top-down effect of fish on the invasive Asian golden mussel's abundance. This work highlights the need to preserve the native fish communities, particularly in South America, where many vulnerable migratory fish are of key relevance as Limnoperna fortunei consumers. In the light of these findings, actions such as implementing efficient fish passage technologies in the actual (and projected) dams of the Uruguay River basin and elsewhere become essential to avoid local extinctions of these natural invasion controls upstream of the dams