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 -https://www.amazon-fish.com/. 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.Scientific Data | (2020) 7:96 | https://doi.collections from Peru 25,26 and by initiating sampling campaigns in detected gaps in Colombia, Peru and Brazil. All these spatial gaps in the database will also be prioritized in future updates through literature and web-based sources checking. Researchers holding fish distribution data from any of the current gaps or under-sampled areas (Fig. 2) and that wish to share these data are welcome to join the project. This information will be included with the complete source, after validation, in the next update of the database.

Amazonian waters are classified into three biogeochemical categories by dissolved nutrient content, sediment type, transparency, and acidity—all important predictors of autochthonous and allochthonous primary production (PP): (1) nutrient-poor, low-sediment, high-transparency, humic-stained, acidic blackwaters; (2) nutrient-poor, low-sediment, high-transparency, neutral clearwaters; (3) nutrient-rich, low-transparency, alluvial sediment-laden, neutral whitewaters. The classification, first proposed by Alfred Russel Wallace in 1853, is well supported but its effects on fish are poorly understood. To investigate how Amazonian fish community composition and species richness are influenced by water type, we conducted quantitative year-round sampling of floodplain lake and river-margin habitats at a locality where all three water types co-occur. We sampled 22,398 fish from 310 species. Community composition was influenced more by water type than habitat. Whitewater communities were distinct from those of blackwaters and clearwaters, with community structure correlated strongly to conductivity and turbidity. Mean per-sampling event species richness and biomass were significantly higher in nutrient-rich whitewater floodplain lakes than in oligotrophic blackwater and clearwater river-floodplain systems and light-limited whitewater rivers. Our study provides novel insights into the influences of biogeochemical water type and ecosystem productivity on Earth’s most diverse aquatic vertebrate fauna and highlights the importance of including multiple water types in conservation planning.

Is there only one electric eel species? For two and a half centuries since its description by Linnaeus, Electrophorus electricus has captivated humankind by its capacity to generate strong electric discharges. Despite the importance of Electrophorus in multiple fields of science, the possibility of additional species-level diversity in the genus, which could also reveal a hidden variety of substances and bioelectrogenic functions, has hitherto not been explored. Here, based on overwhelming patterns of genetic, morphological, and ecological data, we reject the hypothesis of a single species broadly distributed throughout Greater Amazonia. Our analyses readily identify three major lineages that diverged during the Miocene and Pliocene—two of which warrant recognition as new species. For one of the new species, we recorded a discharge of 860 V, well above 650 V previously cited for Electrophorus, making it the strongest living bioelectricity generator.

Floodplains are nutrient-rich systems subject to periodic flooding (Junk, Bayley, & Sparks,) that play important ecological roles for countless species. Amazonian River floodplains are among the most biodiverse and productive ecosystems in the world (Junk, Soares, & Bayley, 2007). In these ecosystems, the seasonal flood pulse is a major driver of patterns of migration, distribution and abundance of

The fishes presented herein were collected in small streams, in channel of lagoons and in the main channel of the Guariba River, as well as in one tributary of the right bank of the Roosevelt River, both clear-water tributaries of Aripuanã River, Madeira River basin. Field work was carried out in November 2008, during the low water season. Sampling resulted in 3924 specimens belonging to 160 species distributed in 34 families, and seven orders. Eight species are recognized as new, two of which were recently described. This study represents the first fish survey for the region and will certainly provide valuable information for future studies and maintenance of the poorly known fish diversity of these two conservation areas.

A new species of Pimelodus LaCépède, 1803 (Siluriformes: Pimelodidae) from the rio São Francisco drainage, BrazilFrank Raynner V. Ribeiro* and Carlos Alberto S. de Lucena** Pimelodus pohli, new species, is described from the rio São Francisco drainage. It differs from congeners by the following characters in combination: adults with dark spots on anterodorsal region of body and young specimens (up to 100 mm SL) with three rows of dark spots laterally on body; comparatively long adipose fin, more than one third of the distance between posterior end of dorsal fin base and the vertical through posterior end of anal-fin base (21.8-26.2% SL); lips poorly developed; 20-25 gill rakers; and maxillary barbels slightly surpassing the caudal-fin base. A key to the species of Pimelodus of the rio São Francisco drainage is presented.Pimelodus pohli, nova espécie, é descrita da bacia do rio São Francisco. Difere de suas congêneres pela seguinte combinação de caracteres: presença, em exemplares adultos, de pintas escuras na região ântero-lateral do corpo e, em exemplares jovens, de três fileiras de pintas nos lados do corpo (até 100 mm CP); nadadeira adiposa comparativamente longa, ocupando mais de um terço da distância entre o fim da base da nadadeira dorsal e a vertical que passa pelo fim da base da nadadeira anal (21,8-26,2% CP); lábios não desenvolvidos; 20 a 25 rastros branquiais e barbilhões maxilares indo pouco além da base da nadadeira caudal. Uma chave para as espécies de Pimelodus da bacia do rio São Francisco é apresentada.

The fish fauna of freshwater streams in the Tapajos National Forest was surveyed and a list of species is presented. The sampling was conducted from 2012 to 2013 during the dry season. Fish were collected with dip nets and seine nets in 22 streams of 1st to 3rd order. Sampling resulted in 3035 specimens belonging to 117 species, 27 families and six orders. The most abundant species were Bryconops aff. melanurus, Hemigrammus belottii, and Hemigrammus analis. Four undescribed species were recognized, one of which is known only from the area of this study. A significant dissimilarity was observed in fish species composition among drainage systems. This is the first survey of the stream ichthyofauna in the Tapajós National Forest, and it presents relevant information for future studies and decision-making in the management and conservation of fish fauna in this conservation unit.

Larval ontogeny of the long-whiskered catfish Pimelodus blochii Valenciennes, 1840 is described, providing useful characters for identification and determining the growth pattern throughout its development. Eighty-nine larvae classified in three stages (preflexion, flexion and postflexion) and 30 juveniles were analyzed, totaling 119 individuals. The specimens were collected monthly from January 2013 to May 2019 in the lower Amazon river. A suite of morphological, morphometric, and meristic data was used to describe the stages of development. Three analytical regression models were used: simple linear, quadratic and piecewise regressions. The larvae are characterized by small to moderate eyes, subinferior mouth, and long barbels (maxillary larger than the mental barbels), triangular-shaped adipose fin, and the final part of the intestine reaching half the body. Pigmentation consists of dendritic chromatophores distributed irregularly in the body, ventral region and head, intensifying in the flanks and dorsal region throughout development. The total number of myomeres has a mode of 42 muscle bundles, ranging from 40 to 42 (15 to 16 pre-and 25 to 26 post-anal) and the number of fin segments corresponded to: pectoral = I + 9, pelvic = 6, dorsal = I + 6 and anal = 11–12. All body variables showed discontinuous isometric growth, indicating a deceleration in the structural modeling of the body, between the flexion/post-flexion stages and acceleration in post-flexion/early juvenile period. Precisely when the formation of the fin rays, muscles and organs of the digestive system and ossification are observed, suggesting low morphological variation during ontogenetic development. Pimelodus blochii differs from other congeneric species in the lower Amazon river by meristic characters, which helps to correctly identify individuals in early stages of development.