This study investigated the effect of hydrological periods on the feeding activity and trophic interactions of four piscivorous fishes from the middle Xingu River, Brazil: pike-characid Boulengerella cuvieri, dogtooth characin Hydrolycus armatus, dogtooth characin Hydrolycus tatauaia and South American silver croaker Plagioscion squamosissimus. Repletion Index (I %), Alimentary Index (I %) and food web properties were calculated for each species. A total of 825 specimens were collected. The I showed changes in feeding intensity of B. cuvieri, H. armatus and H. tatauaia among hydrological periods. Flood pulse showed no influence on composition and importance of food items consumed. Trophic connections showed that connectivity ranged from 0.025 to 0.038. The highest number of trophic connections (75) occurred in the high-water period, when 51 food items were recorded and the lowest number of trophic connections (43) occurred in receding water, with 31 food items. In all food webs, over 45% of food items were consumed by only one species (ultra-peripheral items), which is common in piscivorous fishes.

Length-weight relationships (LWR) were analyzed for 10 fish species from 26 Amazonian streams located in four microbasins in the Trombetas River basin, Par a State, Brazil. LWRs were calculated based on 1831 individuals sampled between 2010 and 2012 using a manual trawl. The coefficients of proportionality and allometry were within the ranges estimated for most fishes. No previous LWR information was available for these species in the literature.

1. Anthropogenic changes in the aquatic environment can influence macroinvertebrate communities, interfering with species richness and diversity. Few studies have investigated the effect of urbanisation in streams using a food web approach. The aim of this study was to describe the food webs of aquatic macroinvertebrates in streams located in urban and preserved areas of the Atlantic Rainforest domain.2. Sampling was conducted in the state of Rio de Janeiro, Brazil, at 10 urban and 10 preserved streams during the dry season (August-September) of 2012. The streams were characterised with respect to their environmental conditions. Macroinvertebrates were sorted and identified in the laboratory and gut contents were examined. Trophic relationships were plotted in consumer-resource food webs and network properties were used to compare the two sets of streams.3. Food webs in urban streams had higher linkage density and connectance, but consumers had fewer items in their guts, which may indicate reduced flow of energy and more unstable food webs. The base of the food webs in each land-use type were also quite different, with higher amounts of plant detritus in preserved streams and fine detritus in urban streams.4. This study shows that preserved areas offer better conditions for the development of macroinvertebrates, resulting in more stable trophic structures when compared with environments under higher anthropogenic influence.

We described the feeding habits of Colomesus asellus from riverbanks of the upper-middle Tocantins River, Central Brazil. Two sampling expeditions were carried out in August (dry season) and in October (rainy season) of 2013, downstream from the Lajeado Hydroelectric Power Plant, Tocantins state. The diet of C. asellus was characterized and compared between juveniles and adults and between individuals captured in the dry season and in the rainy season. Individuals exhibited marked temporal segregation, with a predominance of adults on the riverbanks during the dry season and the predominance of juveniles in the rainy season. The diet of this species was based on diverse benthic prey, mostly Ephemeroptera nymphs (Insecta). Contrary to our expectations, the diet composition of C. asellus was not influenced by seasonal changes or ontogenetic factors, but the size of individuals determined the number of prey consumed. Thus, C. asellus can be classified in its trophic ecology as an insectivore without relation with fish size and seasonality.

Fishes of the order Gymnotiformes have high diversity of oral and head morphology, which suggests trophic specializations within each clade. The aim of this study was to describe resource use patterns by two fish species (Gymnorhamphichthys rondoni and Gymnotus coropinae) in the National Forest Saracá-Taquera, Oriximiná -Pará, analyzing microhabitat use, diet composition, feeding strategies, niche breadth and niche overlap. Stomach contents of 101 individuals (41 G. rondoni and 60 G. coropinae), sampled in 23 headwater streams were analyzed and volume of food items was quantified to characterize their feeding ecology. Gymnorhamphichthys rondoni was captured mainly on sandy bottoms, whereas G. coropinae in crevices. Both species had a zoobenthivorous diet and consumed predominantly Sediment/Detritus and Diptera larvae, but also included allochthonous prey in their diet. These species had high niche overlap, with small variations related to the higher consumption of Ceratopogonidae larvae by G. rondoni and of Chironomidae larvae by G. coropinae. Both species had a generalist feeding strategy, but G. coropinae had a broader niche breadth. Our results demonstrate that G. rondoni and G. coropinae occupy different microhabitats but rely on similar food resources.Keywords: Amazon, Diet overlap, Feeding, Microhabitat, Streams.Peixes da ordem Gymnotiformes apresentam alta diversidade morfológica, o que sugere a existência de especializações tróficas dentro dos clados. O objetivo deste estudo foi analisar o uso de recursos por duas espécies de peixes elétricos (Gymnorhamphichthys rondoni e Gymnotus coropinae) na Floresta Nacional Saracá-Taquera, Oriximiná -Pará, analisando o uso de microhabitats, composição da dieta, estratégias alimentares, amplitude de nicho e sobreposição de nicho. Conteúdos estomacais de 101 indivíduos (41 G. rondoni e 60 G. coropinae), capturados em 23 igarapés de cabeceira, foram analisados e quantificados volumetricamente para a caracterização da ecologia trófica. Gymnorhamphichthys rondoni foi registrada principalmente em bancos de areia, enquanto G. coropinae em fendas. Ambas as espécies apresentaram dieta zoobentívora e consumiram predominantemente sedimento/detritos e larvas de Diptera, mas também consumiram presas alóctones. Foi observada alta sobreposição de nicho trófico e a baixa variação encontrada foi relacionada à maior utilização de larvas de Chironomidae por G. rondoni e de larvas de Ceratopogonidae por G. coropinae. Ambas as espécies apresentaram estratégia alimentar generalista, porém G. coropinae apresentou maior amplitude de nicho. Nossos resultados demonstram que G. rondoni e G. coropinae ocupam microhabitats diferentes, mas dependem de recursos alimentares similares.Palavras-chave: Alimentação, Amazônia, Microhabitat, Riachos, Sobreposição de nicho.

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 by 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. Fatores ambientais influenciam o nicho trófico do tetra Copella arnoldi?Um teste em um sistema lótico amazônico RESUMO 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. PALAVRAS-CHAVE: amplitude de nicho, ecologia trófica, Lebiasinidae, variação ambiental, Amazônia brasileira CITE AS: Soares, B.E.; Benone, N.L.; Rosa, D.C.O.; Montag, L.F.A. 2020. Do local environmental factors structure the trophic niche of the splash tetra, Copella arnoldi? A test in an Amazonian stream system. Acta Amazonica 50: 54-60.

No abstract

Summary Length–weight relationships (LWRs) were analyzed for six abundant fish species in the upper‐middle Tocantins River, northeastern Brazil. Analyses included data from 486 specimens sampled in five expeditions between August 2013 and May 2015 by gillnets. New maximum values of total lengths for the literature and FishBase were presented for six species, as well as first time estimates of LWR for Galeocharax gulo, Curimata acutirostris and Aphanotorulus emarginatus.