The ichthyofauna of the rio Purus has been little investigated, especially in its lower portion, characterized by diverse aquatic environments, especially in flooded areas. We inventoried the ichthyofauna of floodplain lakes with different management efforts in Reserva de Desenvolvimento Sustentável Piagaçu-Purus (RDS-PP), which represent important resource for commercial fishing in North region, in the first illustrated inventory of the fish fauna from lower rio Purus. We surveyed 20 lakes, classified as open access (eight lakes) and protected (12 lakes) during 2009 low water levels. A total of 2,299 individuals were collected, represented by seven orders, 25 families and 74 species. Characiformes was the most representative order in number of species and families, followed by Siluriformes, Cichliformes, Gymnotiformes, Clupeiformes, and Osteoglossiformes. Most abundant and frequent species were Pygocentrus nattereri, Triportheus angulatus, Serrasalmus sp. "2n=58", Pterygoplichthys gibbiceps, and Osteoglossum bicirrhosum. Protected lakes presented higher species richness compared to open access lakes. Similarly, protected lakes possessed 26 species occurring exclusively, with emphasis on Colossoma macropomum, an important species for fisheries due to its commercial importance. We added 44 new records of fish species for the lower rio Purus. Our results indicate the potential efficiency of zoning systems of open access and protected lakes established by local population and ruled by RDS-PP for fisheries management. Therefore, we strongly suggest its maintenance for conservation of ichthyofauna of floodplain lakes of lower rio Purus.

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RESUMENEl Lago Cocibolca merece atención especial por ser una fuente importante de agua para el consumo humano. El río Tepenaguasapa es una de sus subcuencas, que tiene entre otros problemas, la contaminación con nutrientes. Para el estudio de este problema, fue necesario determinar la carga de nutrientes (Fósforo y Nitrógeno) procedentes de las subcuencas. La carga de Fósforo estimada fue de 24.33 t/año y de Nitrógeno de 632.57 t/año, para totalizar 656.89 t/año, con un orden de importancia por su origen de: uso de suelo, precipitación y escurrimiento artificial. El río varía en su estado trófico con un gradiente de concentración de nutrientes aguas arriba hacia aguas abajo. La carga de nutrientes es originada por la gran cantidad de área empleada para pasto y actividad ganadera extensiva, tierras de labranza, monocultivo, manejo de las aguas residuales, tala de árboles, además de ser una cuenca con abundante precipitación y de gran tamaño en comparación con el espejo de agua.Palabras clave: fósforo, nitrógeno, actividad ganadera extensiva, carga de nutrientes, estado trófico. ABSTRACTLake Cocibolca merits special attention as an important source of potable water. The Tepenaguasapa River has a sub watertable which, among other problems, has nutrient contamination. For research into this problem it was necessary to determinate the amount of nutrients (Phosphorus and Nitrogen) in the watertable. The amount of Phosphorus estimated was 24.33 t/year and Nitrogen 632.57ft/year making a total of 656.89 t/year with an order of importance in regard to origin, use of soil, rainfall and artificial water runoff. The river varies in it´s trophic state with a concentration of nutrients in a gradient from upstream to downstream. The nutrient load originates, for the most part, in areas used for pasture and livestock, farming monoculture, waste water management and logging, as well as a river basin which has an abundant rainfall and is of large size compared to the surface water.

The Amazonas River basin comprises the world's highest fish species diversity. Anthropogenic interferences in aquatic environments represent a pressure over the maintenance of ecological stability and biodiversity. We inventoried the ichthyofauna of 13 disturbed/modified tributaries of Urubu and Amazonas rivers in the region of the middle Amazon River, between June 2018 and March 2019. A total of 164 species were captured, represented by 11 orders, 37 families and 96 genera. Characiformes was the richest order, followed by Cichliformes and Siluriformes. The most representative families in number of species were Cichlidae, Serrasalmidae, and Characidae. Hemigrammus levis was the most abundant species, and Acarichthys heckelii the most common, registered in all sampled sites. In the present study, species with economic interest were collected, as well as many species recently described and one still waiting for formal description, identified provisionally as Moenkhausia aff. colletii. Therefore, the high fish diversity registered, even in disturbed environments in Middle Amazonas River, denotes the makeable ecological importance of this region for fishes resources and supports the necessity of evaluation of other aquatic environments in the region, as well as the potential impacts on composition, maintenance, and survival of ichthyofauna in environments directly affected by human activities.Resumo: A bacia do rio Amazonas compreende a maior diversidade de espécies de peixes do mundo. Interferências antropogênicas em ambientes aquáticos representam uma pressão sobre a manutenção da estabilidade ecológica e da biodiversidade. Inventariamos a ictiofauna de 13 afluentes perturbados/modificados dos rios Urubu e Amazonas na região do médio do rio Amazonas, entre junho de 2018 e março de 2019. Foram capturadas 164 espécies no total, representadas por 11 ordens, 37 famílias e 96 gêneros. Characiformes foi a ordem mais rica, seguida por Cichliformes e Siluriformes. As famílias mais representativas em número de espécies foram Cichlidae, Serrasalmidae e Characidae. Hemigrammus levis foi a espécie mais abundante e Acarichthys heckelii a mais comum, registrada em todos os locais amostrados. No presente estudo foram coletadas espécies de interesse econômico, bem como muitas espécies recentemente descritas e uma ainda aguardando descrição formal, identificada provisoriamente como Moenkhausia aff. colletii. Portanto, a alta diversidade de peixes registrada, mesmo em ambientes perturbados no médio rio Amazonas, denota a importância ecológica marcante dessa região para os recursos pesqueiros e suporta a necessidade de avaliação de outros ambientes aquáticos da região, bem como os possíveis impactos na composição, manutenção e sobrevivência da ictiofauna em ambientes diretamente afetados pelas atividades humanas. Palavras-chave: Diversidade da ictiofauna, Impactos ambientais, Inventário, Peixes amazônicos. Pereira, RS. et al.