The degradation of riparian vegetation in low-order streams can cause irreversible environmental damage, biodiversity loss and alter the structure of communities. In this context, the present study evaluated how the level of degradation of riparian vegetation influences the fish assemblage in three low-order streams in the Brazilian Amazon. In each stream, three different stretches were delimited, distributed in the environments of forest, edge and pasture, and the samplings were conducted in three hydrological regimes using dip nets. Influences of the stretches and streams on richness and abundance were tested with GLMM, on the composition with PERMANOVA and on indicator species with IndVal. Species richness was higher in forest environments and lower in pasture; while abundance was higher in pasture and lower in forest. Species composition differed between stretches, streams and in the interaction between stretches and streams, with a strong difference between stretches of forest and pasture environments. Six species dependent of the riparian vegetation were classified as indicators of forest environments; while a generalist species was indicator of pasture. These results reinforce the negative influence of riparian vegetation removal on biological communities and provide subsidies that can help in the conservation and management of these systems.

The length‐weight relationship (LWRs) was estimated for eight fish species collected from oxbow lakes on the floodplain of the middle Purus River in western Brazilian Amazonia in January, May, and September 2012. The specimens were collected using 12 gillnets (80 m in length × 4 m in height, meshes of between 1.5 cm and 12.0 cm), which were set during both diurnal and nocturnal periods. The species had allometric coefficients (b) of between 2.92 and 3.37, and correlation coefficients (r2) ranging from 0.954 to 0.993 and we highlight that the work presents new data for literature.

The effect of the flood pulse directs productivity and interactions of biota in abandoned oxbow lakes, as these habitats provide refuge from predators and serve as nurseries and feeding grounds for many fish species. The present study was conducted in twelve oxbow lakes with varying degrees of connectivity, located in the floodplain of the Middle Purus River in Brazil. 8.647 individuals were collected among 157 species. Lakes with high hydrological connectivity were shown to have the largest richness of species (131 species), while lakes with medium connectivity had slightly smaller richness (123 species), and lakes with low connectivity had even less (113 species). The results show high diversity in lakes that are attributed different connectivity, thereby indicating the importance of studies focused on oxbow lakes that contribute with relevant information on the composition of fish species in the Middle Purus River.

The trophic structure of fish assemblages associated with banks of aquatic macrophytes in abandoned meander lakes on the river Purus is investigated. Comparisons between lakes and between different periods of the hydrological cycle are undertaken. Fish samples were collected in six lakes during the rainy (February), ebb (May) and dry (September) season in 2012. Fish stomach contents were analyzed by frequency of occurrence and volume methods, combined in the Feeding Index (IAi). Fish species were included in nine trophic categories, based on IAi rates. The richness and abundance of fish species, by trophic category, was influenced by temporal variations, with no significant spatial variation. Some species changed their diets and were included in different trophic categories according to the period and lake under analysis. Specialist species have also been identified, but failed to change their diets. Differences may be due to the characteristics of macrophytes banks and to the flooding regime which change the availability of food resources.

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A discussão de estudos sobre os fenômenos atmosféricos que causam modificações na precipitação pluviométrica é essencial para a compreensão da variabilidade espaço-temporal das chuvas e entendimento acerca dos eventos extremos de baixa e alta precipitação local que podem trazer danos tantos ambientais como sociais. Desta forma, o presente trabalho tem como objetivo discutir sobre a relação dos fenômenos atmosféricos que influenciam a precipitação no estado do Acre e o uso do Índice de Anomalia de Chuva (IAC) como ferramenta de avaliação da precipitação pluviométrica. A metodologia está centrada na leitura de trabalhos publicados em revistas eletrônicas, buscando artigos científicos em diferentes plataformas internacionais e nacionais com abordagens sobre a influência de fenômenos atmosféricos na precipitação pluviométrica. O trabalho trata de uma abordagem meramente teórica, porém, importante para a difusão do conhecimento nesta área da ciência. Dessa forma, dentre os fenômenos climáticos que ocasionam mudanças significativas no regime das chuvas no estado do Acre estão às flutuações interanuais na oscilação sul e a pressão atmosférica ao nível do mar no oceano Pacífico, nos quais influência na intensidade dos fenômenos de El Niño e La Niña. Possivelmente, esses eventos causam alterações no regime de ventos alísios que se movimentam na zona de convergência intertropical, no qual influência de maneira positiva ou negativa nos padrões pluviométricos da Amazônia. Entretanto, como ferramenta precisa de verificação da variabilidade pluviométrica ao longo de uma série histórica em determinado espaço o índice de anomalia de chuva torna-se a principal ferramenta, no qual é possível a identificação de eventos extremos de alta e baixa precipitação em uma série histórica de uma dada região.

Most freshwater species of Cymothoidae are distributed in South America. They have mainly been recorded in the eastern and western regions of the Amazon River basin. However, in this ecosystem, the biodiversity of this group may be greater if the entire Amazon basin is considered. In this regard, the aim of the present study was to provide an updated list of isopod species of the family Cymothoidae that are found in fish in the Brazilian Amazon region and to report on new fish host occurrences and expanded geographical distributions for cymothoid isopods that parasitize fish in the southwestern Brazilian Amazon region. The parasites found in fish specimens were collected, fixed and identified later. We found eight species of Cymothoidae parasitizing different host fish species in the southwestern Amazon region. However, we found 14 species of Cymothoidae throughout the Brazilian Amazon region. Three additional species are thus reported here, which increases the number of species of Cymothoidae in this region to 17. These additional species are also new records for Brazil. Therefore, this study has contribute to expand the knowledge about the distribution and diversity of Cymothoidae in the Amazon basin.

A destruição de habitats, promovida pela extração de areia de leitos de riachos, pode causar a perda de algumas espécies e a alteração na dinâmica das assembleias de peixes. Assim, o presente estudo investigou o efeito da extração de areia sobre as assembleias de peixes em riachos de Campinarana, localizados na região de Cruzeiro do Sul, Acre, entre junho a agosto de 2017 e 2018. Seis riachos foram avaliados, sendo três degradados (pela extração de areia) e três florestados. Riqueza, diversidade de Shannon, equitabilidade e abundância de espécies foram avaliadas. Para verificar diferenças entre esses parâmetros, foi realizado o teste t de Student. NMDS e PERMANOVA foram sumarizadas para avaliar a composição de espécies de peixes. Foram coletadas 60 espécies de peixes com 705 indivíduos. Houve uma diferença significativa entre as áreas com relação à riqueza (t = 11,1; p = 0,0001), à abundância (t = 4,5; p = 0,006) e à diversidade (t = 4,1; p = 0,01). A composição de espécies também variou (Pseudo-F = 3,79; p = 0,01), onde 35% das espécies foram restritas aos ambientes preservados. Assim, sugere-se que a perturbação antrópica nas campinaranas, causou perda das espécies mais sensíveis e especializadas, permitindo o aumento dos indivíduos oportunistas, alterando a organização das assembleias e reduzindo a diversidade local.