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The Amazon Basin is an unquestionable biodiversity hotspot, containing the highest freshwater biodiversity on earth and facing off a recent increase in anthropogenic threats. The current knowledge on the spatial distribution of the freshwater fish species is greatly deficient in this basin, preventing a comprehensive understanding of this hyper-diverse ecosystem as a whole. Filling this gap was the priority of a transnational collaborative project, i.e. the AmazonFish project - . Relying on the outputs of this project, we provide the most complete fish species distribution records covering the whole Amazon drainage. The database, including 2,406 validated freshwater native fish species, 232,936 georeferenced records, results from an extensive survey of species distribution including 590 different sources (e.g. published articles, grey literature, online biodiversity databases and scientific collections from museums and universities worldwide) and field expeditions conducted during the project. This database, delivered at both georeferenced localities (21,500 localities) and sub-drainages grains (144 units), represents a highly valuable source of information for further studies on freshwater fish biodiversity, biogeography and conservation.

In the Amazon, migratory catfishes of the genus Brachyplatystoma are apex predators that are important for fisheries and conservation. The life cycle of Brachyplatystoma platynemum Boulenger, 1898 is poorly known, although it has been hypothesized to be very similar to that of Brachyplatystoma rousseauxii Castelnau, 1855, which uses the entire length of the Amazon basin to complete its life cycle (from the Andes to the estuary). This study provides the first data on the migratory patterns of B.platynemum at the individual level using otolith microchemistry. In total, 94 individuals were sampled close to major breeding areas in the Amazon basin (78 fish from the middle and upper Madeira River and 14 fish from the upper Amazon), and their lifetime movements were assessed by measuring variations in Sr-87/Sr-86 along transverse sections of their otoliths (ear stones), using laser ablation multi-collector mass spectrometry (LA-MC-ICP-MS). The migrations of B.platynemum are not as extensive as those of B.rousseauxii, and do not involve natal homing. Furthermore, the estuary is not a nursery area, at least for fish hatched in the Madeira. Nevertheless, B.platynemum migrates several thousand kilometres within the Amazon basin, with transboundary displacements between at least Bolivia, Brazil, and Peru. Current and planned hydroelectric development in the Amazon basin will severely disrupt both migration and access to breeding grounds, ultimately affecting the recruitment and population dynamics of these apex predators. The conservation of B.platynemum is crucial for the stability of the Amazonian aquatic food webs. This requires building effective fish passage on the two existing Madeira dams and considering alternative options to the large-scale hydropower development in the Amazon basin.

The Madeira River, which drains one of the major tributary river basins of the upper Amazon, contributes to small-scale fisheries in Peru, Bolivia, and Brazil. This paper provides a base-line of fisheries resources and their status in six sub-basins of the Madeira River: upper Madre de Dios River basin (Peru), Beni and Mamore River basins (Bolivia), Itenez or Guapore River basin (Bolivia and Brazil), middle Madeira, and (two sections of the) lower Madeira River (Brazil). Data were collected between 2009 and 2011, before the completion of two hydroelectric dams in the Brazilian portion of the basin. Biophysical, social, and biological indicators were used to characterize the fisheries. The results show an overall small-scale multispecies fisheries pattern but with notorious differences between the Madeira sub-basins. The Beni and Mamore sub-basin shows the largest flooded area, with associated higher total fisheries yields. Trophic level of the catch, diversity, and mean weight of fish caught were shown to be very sensitive to exploitation level, river water type (white or clear water), flooded area, and the introduction of Arapaima gigas in Bolivia. The Bolivian fisheries are characterized by less exploited stocks, whereas stocks in Peru and Brazil show signs of intensive exploitation, resulting in fisheries of smaller bodied, lower trophic-level species. Landing data in the upper basin show a predominant reliance on migrating fish resources, which might be vulnerable to the construction of dams. These data serve as a baseline to evaluate anthropogenic impacts on the Madeira River basin fisheries in the future.

The goliath catfish Brachyplatystoma rousseauxii has crucial economical and ecological functions in the Amazon basin. Although its life history characteristics have been studied in the Amazon, there is little information in the Madeira River basin, which holds genetically distinct populations and where dams were recently built. Using fish collected in Bolivia, Brazil and Peru, this study provides a validation of growth rings deposition and details the growth patterns of B. rousseauxii in the Madeira before the dams' construction. Age structure and growth parameters were determined from 497 otolith readings. The species exhibits two growth rings per year and sampled fish were between 0 and 16 years old. In the Brazilian portion of the basin, mainly young individuals below 5 years old were found, whereas older fish (> 5 years) were caught only in the Bolivian and Peruvian stretches, indicating that after migrating upstream to reproduce, adults remain in the headwaters of the Madeira River. Comparing with previous publications, B. rousseauxii had a slower growth and 20 cm lower maximum standard length in the Madeira River than in the Amazon River. This study provides a baseline for future evaluation of changes in population dynamics of the species following dams closure.