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ABSTRACT The ecomorphology reflects morphological variations that may indicate significant ecological processes. In this study, the influence of environmental variables on the ecomorphological composition of stream fish was tested. The study was developed in ten streams within a conservation area in the Juruena River sub-basin, in Mato Grosso state, Brazil. The sampling occurred during the drought period in July 2012. The fish were sampled with simple sieves and trawl nets. We analyzed 17 variables of the physical habitat and 14 morphological indices based on morphometric measurements of the fish. In total, 753 specimens were collected, comprising four orders, 14 families, and 27 species. Only fine sediments influenced the ecomorphological composition of the fish assemblages. This substrate variable acted as a filter for the ecomorphology of fish that usually inhabit slow waters, have a morphology adapted towards a good stabilization capacity and maneuverability, fins capable of large and rapid impulses, and that feed close to the surface. Our results can contribute to the understanding of the ecological processes that drive the composition of fish assemblages in conserved Amazonian streams.

RESUMO A ecomorfologia reflete variações morfológicas que podem indicar processos ecológicos significativos. Neste estudo, testamos a influência de variáveis ambientais na composição ecomorfológica de peixes de riachos. O estudo foi desenvolvido em dez riachos em uma área de conservação na sub-bacia do Rio Juruena, estado de Mato Grosso, Brasil. A amostragem ocorreu durante o período de estiagem em julho de 2012. Os peixes foram amostrados com redes de peneira e redes de arrasto. Foram analisadas 17 variáveis do habitat físico e 14 índices morfológicos baseados em medidas morfométricas dos peixes. No total, foram coletados 753 exemplares de quatro ordens, 14 famílias e 27 espécies. Apenas sedimentos finos influenciaram a composição ecomorfológica das assembleias de peixes. Esta variável de substrato funcionou como um filtro para a ecomorfologia de peixes que normalmente habitam águas lentas, têm uma morfologia adaptada a uma boa capacidade de estabilização e manobrabilidade, nadadeiras capazes de impulsos grandes e rápidos, e que se alimentam junto à superfície. Nossos resultados podem contribuir para a compreensão dos processos ecológicos que estruturam as assembléias de peixes em riachos amazônicos conservados.

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We assessed the flood pulse effect on the diet composition, trophic niche breadth, and the amount of food intake of two Amazonian auchenipterids with different feeding strategies. Sampling was carried out quarterly (from April/2012 to January/2014) on the middle Xingu River, using gillnets. We measured specimens for standard length and total weight. The specimens' stomachs were removed, weighed, and had their contents identified. We analyzed 360 stomachs of Auchenipterus nuchalis and 584 of Tocantinsia piresi. The diet of A. nuchalis was mainly composed of aquatic insects and crustaceans, while T. piresi fed on fruits and seeds. The diet composition of both species varied seasonally, but only T. piresi changed its trophic niche breadth in response to hydrological changes, becoming more specialist during the higher water periods (filling and flood). Both species also showed differences in their amount of food intake between hydrological periods, with A. nuchalis feeding more intensely in lower water periods (ebb and dry), while T. piresi in the higher water periods. We evidenced different responses to the hydrological periods for the related species. We emphasize that studies considering the relationship between flood pulse and feeding ecology of the organisms are essential to understanding river floodplain systems' dynamics.(AU)

Avaliamos o efeito do pulso de inundação na composição da dieta, amplitude de nicho trófico e quantidade de alimento ingerido de dois auchenipterídeos amazônicos com diferentes estratégias alimentares. Os espécimes foram amostrados trimestralmente entre abril/2012 e janeiro/2014 no médio rio Xingu, utilizando malhadeiras. Estes foram mensurados quanto ao comprimento padrão e peso total. Os estômagos dos espécimes foram removidos, pesados e seu conteúdo identificado. Analisamos 360 estômagos de Auchenipterus nuchalis e 584 de Tocantinsia piresi. A dieta de A. nuchalis foi predominantemente composta por insetos aquáticos e crustáceos, enquanto para T. piresi frutos e sementes predominaram. A composição da dieta de ambas as espécies variou sazonalmente, mas apenas para T. piresi a amplitude de nicho trófico variou entre períodos hidrológicos, sendo mais especialista nos períodos de águas altas (enchente e cheia). Ambas as espécies diferiram na quantidade de alimento ingerido entre os períodos hidrológicos, sendo maior para A. nuchalis nos períodos de águas baixas (vazante e seca) e para T. piresi nos períodos de águas altas. Evidenciamos diferentes respostas à variação hidrológica pelas espécies. Enfatizamos que estudos considerando a relação entre a dinâmica do pulso de inundação e a ecologia alimentar dos organismos é fundamental para um melhor entendimento da dinâmica das planícies de inundação.(AU)

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In community ecology, it is important to understand the distribution of communities along environmental and spatial gradients. However, it is common for the residuals of models investigating those relationships to be very high (> 50%). It is believed that species' intrinsic characteristics such as rarity can contribute to large residuals. The objective of this study is to test the relationship among communities and environmental and spatial predictors by evaluating the relative contribution of common and rare species to the explanatory power of models. Our hypothesis is that the residual of partition the variation of community matrix (varpart) models will decrease as rare species get removed. We used several environmental variables and spatial filters as varpart model predictors of fish and Zygoptera (Insecta: Odonata) communities in 109 and 141 Amazonian streams, respectively. We built a repetition structure, in which we gradually removed common and rare species independently. After the repetitions and removal of species, our hypothesis was not corroborated. In all scenarios, removing up to 50% of rare species did not reduce model residuals. Common species are important and rare species are irrelevant for understanding the relationships among communities and environmental and spatial gradients using varpart. Therefore, our findings suggest that studies using varpart with single sampling events that do not detect rare species can efficiently assess general distributional patterns of communities along environmental and spatial gradients. However, when the objectives concern conservation of biodiversity and functional diversity, rare species must be carefully assessed by other complementary methods, since they are not well represented in varpart models.

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Pollution by plastics is a global problem, in particular through the contamination of aquatic environments and biodiversity. Although plastic contamination is well documented in the aquatic fauna of the oceans and large rivers of the world, there are few data on the organisms of headwater streams, especially in tropical regions. In the present study, we evaluated the contamination of small fish by plastics in Amazonian streams. For this, we evaluated the shape and size, and the abundance of plastics in the gastrointestinal tracts and gills of 14 fish species from 12 streams in eastern Brazilian Amazon. We used a Generalized Linear Mixed Model (GLMM) to compare the levels of contamination among species and between organs. Only one individual of the 68 evaluated (a small catfish Mastiglanis cf. asopos) contained no plastic particles, and no difference was found in the contamination of the gills and digestive tract. However, Hemigrammus unilineatus presented less contamination of both the gills and the digestive tract than the other species, while Polycentrus schomburgkii had less plastic in the gastrointestinal tract, whereas Crenicichla regani and Pimelodella gerii both had a larger quantity of plastic adhered to their gills in comparison with the other species. Nanoplastics and microplastics adhered most to the gills, while plastic fibers were the most common type of material overall. This is the first study to analyze plastic contamination in fish from Amazonian streams, and in addition to revealing high levels of contamination, some species were shown to possibly be more susceptible than others. This reinforces the need for further, more systematic research into the biological and behavioral factors that may contribute to the greater vulnerability of some fish species to contamination by plastics. Amazonian stream fish show contamination by plastics. The species respond differently. The smaller the particle, the easier it is to adhere to the gills.

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Environmental variation affects the availability of spatial and trophic resources in Amazonian streams and may be important factors structuring the diet of fishes. We analyzed the diet composition and trophic niche breadth of the lebiasinid splash tetra, Copella arnoldi, aiming to evaluate how environmental variation in Amazonian streams affects the species' trophic niche. Fish were captured and environmental factors were recorded in 20 streams in the Caxiuanã National Forest, in the eastern Amazon, in November 2010. We made a semi-quantitative analysis of stomach contents of 200 individuals. Copella arnoldi exhibited an omnivorous diet composed mainly of detritus and allochthonous invertebrates. Environmental variation (stream width, stream depth, canopy cover and flow) did not affect the diet composition or trophic niche breadth of the species, possibly due to the regional integrity of the forest within the boundaries of the protected area. Riparian cover probably minimizes the effect of the small-scale variations in food resources, thus leading to a locally homogeneous diet composition in the splash tetra C. arnoldi. (AU)

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Sublethal exposures to environmental pollutants may cause changes in physiological parameters. Thus, knowledge of basal physiological rates of the species and the development of methods to quantify these rates are extremely important. Considering the scarcity of cardiac and muscle physiological studies in native Amazonian fish species and that no evaluation of electrophysiological responses by exposure to a stressor has been reported in Bryconops caudomaculatus, the aim of this study was to develop techniques of electromyographic and electrocardiographic recordings of normal responses, during toxicity induction and short-term recovery. A total of 9 animals were used, divided into two groups: control group (n = 4) and treated group (n = 5), with records lasting 5 min. The results showed that the basal electromyographic records indicate that the studied species has a very intense swimming activity, whereas the basal cardiac parameters clearly showed the patterns in P wave tracing, QRS complex, T wave and Q-T and R-R intervals. During exposure to the stressor, muscle activity ceased presenting intense decrease and myorelaxant effect expected. Electrocardiographic responses confirmed cardiotoxicity with intense bradycardia, ventricular bigeminism, prolongation of QRS complex duration and cardiac arrhythmias, indicating cardiac dysfunction. It was concluded that the electrophysiological responses are excellent biomarkers and showed the susceptibility of the species to the tested substance. In addition, the electrocardiogram and the electromyogram are excellent techniques to reflect the degree of environmental stress when organisms are exposed to toxic substances in the environment.

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Spatial and temporal variations in streams promote large fluctuations of resource availability, thus affecting the diet of fishes. We evaluated the effects of hydrological periods and stream order within periods on the diet of the flag tetra Hyphessobrycon heterorhabdus. We analyzed 160 stomachs in eight streams ranging from 1st to 3rd order between dry and flood period. Sampled streams belonged to a well-preserved area in the Eastern Amazon. The flag tetra is omnivorous, with a tendency towards insectivory. During the dry period, the species exhibited a higher amount of autochthonous than allochthonous items. Fish consumed more allochthonous items in 1st and 2nd order streams in the dry period and in 1st and 3rd order streams in the flood period. These results reflect the interactions between temporal and longitudinal factors on resource availability and its influence on fish diet. This pattern is probably dependent on the extensive riparian vegetation as a direct and indirect source of food for stream fish.(AU)

Variações espaciais e temporais em habitats de riachos promovem grandes flutuações na disponibilidade de recursos, afetando assim a dieta dos peixes. Avaliamos os efeitos dos períodos hidrológicos e da ordem do riacho em cada período na dieta do tetra Hyphessobrycon heterorhabdus. Analisamos 160 estômagos em oito riachos variando de 1ª a 3ª ordem entre o período de seca e cheia. Todos os riachos foram amostrados em uma área bem preservada na Amazônia Oriental. O tetra é onívoro com tendência à insetivoria. Durante o período seco, a espécie exibiu maior quantidade de itens autóctones do que itens alóctones. Os peixes consumiram mais itens alóctones nos riachos de 1ª e 2ª ordem no período de seca e nos riachos de 1ª e 3ª ordem no período de cheia. Esses resultados refletem as interações entre fatores temporais e longitudinais na disponibilidade de recursos e sua influência na dieta de peixes. Este padrão é provavelmente dependente da extensa vegetação ripária como fonte direta e indireta de alimento para peixes de riachos.(AU)

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Environmental variation affects the availability of spatial and trophic resources in Amazonian streams and may be important factors structuring the diet of fishes. We analyzed the diet composition and trophic niche breadth of the lebiasinid splash tetra, Copella arnoldi, aiming to evaluate how environmental variation in Amazonian streams affects the species trophic niche. Fish were captured and environmental factors were recorded in 20 streams in the Caxiuanã National Forest, in the eastern Amazon, in November 2010. We made a semi-quantitative analysis of stomach contents of 200 individuals. Copella arnoldi exhibited an omnivorous diet composed mainly of detritus and allochthonous invertebrates. Environmental variation (stream width, stream depth, canopy cover and flow) did not affect the diet composition or trophic niche breadth of the species, possibly due to the regional integrity of the forest within the boundaries of the protected area. Riparian cover probably minimizes the effect of the small-scale variations in food resources, thus leading to a locally homogeneous diet composition in the splash tetra C. arnoldi.(AU)

Variações ambientais afetam a disponibilidade de recursos espaciais e tróficos em igarapés amazônicos e podem ser fatores importantes estruturando a dieta de peixes. Analisamos a composição da dieta e a amplitude de nicho trófico do lebiasinídeo Copella arnoldi, tendo como objetivo avaliar como a variação ambiental em igarapés amazônicos afeta o nicho trófico da espécie. Indivíduos foram capturados e fatores ambientais foram medidos em 20 igarapés da Floresta Nacional de Caxiuanã, na Amazônia Oriental, em Novembro de 2010. Fizemos uma análise semi-quantitativa do conteúdo estomacal de 200 indivíduos. Copella arnoldi apresentou uma dieta onívora composta predominantemente por detritos e invertebrados alóctones. A variação ambiental (largura e profundidade do igarapé, cobertura de dossel e correnteza) não afetaram a composição da dieta ou a amplitude de nicho trófico da espécie, possivelmente devido à integridade regional da floresta na área protegida. A cobertura ripária provavelmente minimiza os efeitos da variação ambiental nos recursos tróficos, levando, assim, a uma dieta localmente homogênea de C. arnoldi.(AU)

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Spatial and temporal variations in streams promote large fluctuations of resource availability, thus affecting the diet of fishes. We evaluated the effects of hydrological periods and stream order within periods on the diet of the flag tetra Hyphessobrycon heterorhabdus. We analyzed 160 stomachs in eight streams ranging from 1st to 3rd order between dry and flood period. Sampled streams belonged to a well-preserved area in the Eastern Amazon. The flag tetra is omnivorous, with a tendency towards insectivory. During the dry period, the species exhibited a higher amount of autochthonous than allochthonous items. Fish consumed more allochthonous items in 1st and 2nd order streams in the dry period and in 1st and 3rd order streams in the flood period. These results reflect the interactions between temporal and longitudinal factors on resource availability and its influence on fish diet. This pattern is probably dependent on the extensive riparian vegetation as a direct and indirect source of food for stream fish.(AU)

Variações espaciais e temporais em habitats de riachos promovem grandes flutuações na disponibilidade de recursos, afetando assim a dieta dos peixes. Avaliamos os efeitos dos períodos hidrológicos e da ordem do riacho em cada período na dieta do tetra Hyphessobrycon heterorhabdus. Analisamos 160 estômagos em oito riachos variando de 1ª a 3ª ordem entre o período de seca e cheia. Todos os riachos foram amostrados em uma área bem preservada na Amazônia Oriental. O tetra é onívoro com tendência à insetivoria. Durante o período seco, a espécie exibiu maior quantidade de itens autóctones do que itens alóctones. Os peixes consumiram mais itens alóctones nos riachos de 1ª e 2ª ordem no período de seca e nos riachos de 1ª e 3ª ordem no período de cheia. Esses resultados refletem as interações entre fatores temporais e longitudinais na disponibilidade de recursos e sua influência na dieta de peixes. Este padrão é provavelmente dependente da extensa vegetação ripária como fonte direta e indireta de alimento para peixes de riachos.(AU)

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A field study of the sex ratio, length-weight ratio, body size at first gonadal maturation, and the breeding season of the red-tailed catfish, Phractocephalus hemioliopterus, was carried out in the region of the middle Xingu River in the eastern Amazon basin. The fish were sampled quarterly from September 2012 to January 2014 using gillnets and long lines. The sex ratio was balanced, and while males and females were similar in standard length, the females were heavier than the males, on average. The males presented negative allometric growth, and the females, isometric growth. The estimated size at first maturity was 77.8 cm. The variation in the gonadosomatic index and the greater frequencies of mature specimens indicated a reproductive peak at the beginning of the high-water (flood) period. As P. hemioliopterus is an important commercial fish, our findings will contribute to the future development of effective conservation and management strategies, such as minimum catch size and a close season that is appropriate for the region. These data will also provide important insights for the evaluation of potential impacts on the biology of this fish resulting from the construction of Belo Monte dam.(AU)

Um estudo de campo sobre a proporção sexual, relação peso-comprimento, tamanho de primeira maturação gonadal e o período reprodutivo da pirarara, Phractocephalus hemioliopterus foi realizado na região do Médio Rio Xingu, na Amazônia oriental. Os espécimes foram coletados trimestralmente entre setembro de 2012 e janeiro de 2014, utilizando redes malhadeiras e espinheis. A proporção sexual foi balanceada, e machos e fêmeas foram equivalentes quanto ao comprimento padrão, mas fêmeas foram mais pesadas do que machos. Crescimento alométrico negativo foi evidenciado para machos e crescimento isométrico para fêmeas. O tamanho estimado de primeira maturação sexual foi igual a 77,8 cm. A variação do índice gonadossomático e a maior frequência de indivíduos maduros evidenciaram uma maior atividade reprodutiva no começo do período de águas altas (enchente). Considerando P. hemioliopterus como uma espécie de interesse comercial, as informações aqui apresentadas poderão ser uteis para um futuro plano de conservação e manejo como o estabelecimento de um tamanho mínimo de captura e período de defeso para a região. Além disso, poderá ser útil para avaliar potenciais impactos na biologia dos peixes em decorrência das mudanças ambientais provocadas pela construção da barragem de Belo Monte.(AU)

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