ABSTRACT. Feeding and ecomorphological patterns of stream-dwelling fishes from the upper Tocantins river, Goiás, Brazil. In the present study we aimed to compare ecomorphological and feeding data of 18 stream-dwelling fish species from the upper Tocantins river, in order to test if morphological patterns confirm the trophic ones and if they could be used as predictive characters in the analysis of the trophic structure of this community. Feeding analysis revealed a wide range of food items consumed by the fishes and allowed the recognition of three major trophic groups: carnivorous/insectivorous/piscivorous, omnivorous and detritivorous/herbivorous. Principal Component Analysis, based on the morphometric indices, organized the studied species according to head size, eye diameter, mouth position and body depth and allowed the recognition of two major ecomorphological groups. We concluded that the ecomorphological analysis efficiently described specific ecological characters, reflected feeding and habitat use preferences and could be used as trophic structure predictors of the studied community. KEYWORDS.Trophic ecology, stream-dwelling fishes, Amazon basin, allochthonous resources, autochthonous resources. RESUMO.No presente trabalho, comparamos a morfologia e o hábito alimentar de 18 espécies de peixes do alto rio Tocantins a fim de verificar se os padrões morfológicos obtidos para o conjunto das espécies estudadas corroboram os padrões tróficos e, portanto, se podem ser usados como caracteres preditivos da estrutura trófica da comunidade. A análise da dieta revelou ampla variedade de itens consumidos e distinção de três grandes grupos tróficos: espécies carnívoras/insetívoras/piscívoras, onívoras e herbívoras. A Análise dos Componentes Principais, baseada nos índices morfológicos, determinou a ordenação das espécies de acordo com tamanho da cabeça, diâmetro do olho, posição da boca e altura do corpo e permitiu a distinção de dois grandes grupos de espécies. Os grupos obtidos a partir dos índices morfológicos corroboram o padrão obtido a partir da análise da dieta das espécies. A análise ecomorfológica revelou-se uma ferramenta adequada na descrição de aspectos ecológicos das espécies estudadas, refletindo preferências alimentares e de uso do hábitat e pode ser usada como método preditivo da estrutura trófica da comunidade estudada. PALAVRAS-CHAVE.Ecologia trófica, peixes de riachos, bacia Amazônica, recursos alóctones, recursos autóctones.A relação entre morfologia e comportamento ecológico tem sido investigada em populações de diversos sistemas fluviais e comunidades de peixes (e.g.

ABSTRACT. In this contribution we studied the trophic ecology of four Characidae species from the Cavalo Stream, upper Tocantins River, considering diet overlap and trophic niche breadth. The diet of the four species was composed of adult and immature insects, both autochthonous and allochthonous in origin. Autochthonous items dominated the diet of Moenkhausia dichroura (Kner, 1858), Bryconamericus sp., and Creagrutus atrisignum Myers, 1917. By contrast, allochthonous items were dominant in the diet of Astyanax bimaculatus (Linnaeus, 1758). Trophic niche breadth varied among species, with the highest value recorded for M. dichroura (0.48), followed by Bryconamericus sp. (0.39), A. bimaculatus (0.33) and C. atrisignum (0.29). Similarity analysis revealed two groups with different patterns of food preference. The first group was composed of insectivorous and the second by omnivorous species. The overlap in food items consumed by the four species studied was high. We suggest that resources are not limited in this stream and that competition might not be regulating these populations. This is one more case corroborating the general pattern registered for Tropical environments, where resource partitioning and specialization are responsible by the organization of fish communities.

Aquatic animals provide nutrients, mostly nitrogen (N) and phosphorus (P), to the ecosystem throughexcretion of metabolic waste. Excretion rates of N and P are determined by physiological requirements and dietintake and can be affected by several factors, such as body size, resource acquisition, and body elemental composition.Here, we investigated if diet and body elemental composition affect excretion rates in two taxa, shrimp andfish, which differ greatly in their elemental content. Shrimp and fish are often very abundant and can be major mineralizersin oligotrophic tropical streams. We measured per capita and mass-specific excretion rates of ammonium(NH4+-N) and soluble reactive phosphorus (SRP) of two fish (Bryconamericus microcephalus and Characidiumjapuhybense) and two shrimp species (Macrobrachium olfersii and Potimirim brasiliana) from a Brazilian stream.We hypothesized that fish, due to their higher P demand (because of their bony structure), excrete less P and higherN:P ratios compared with shrimp. Contrary to our expectations, fish and shrimp did not differ in their mass-specificSRP excretion rates even if fish had higher body %P. The N:P excretion ratio did not follow ecological stoichiometrypredictions either, as the species with the highest N:P excretion ratio was the herbivorous shrimp P. brasilianaand the other three species did not differ between each other. Diet was not a good predictor either, as excretion ratesof both N and P did not reflect the species trophic position (e.g. the herbivorous shrimp had higher per capita Nexcretion rates than the omnivorous shrimp). Our results suggest that factors other than bone tissue investment anddiet are affecting consumer excretion rates. Consumption rates, assimilation efficiency, metabolic requirements andtaxa-specific physiological mechanisms could be having a major role in controlling excretion rates of our studiedspecies. More field studies on diverse taxa and controlled laboratory experiments are necessary to understand therelative roles of different factors in regulating excretion rates.

Key to understand predator choice is the relationship between predator and prey abundance. There are few studies related to prey selection and availability. Such an approach is still current, because the ability to predict aspects of the diet in response to changes in prey availability is one of the major problems of trophic ecology. The general objective of this study was to evaluate prey selection by two species (Characidium cf. vidali and Pimelodella lateristriga) of the Mato Grosso stream, in Saquarema, Rio de Janeiro, Brazil. Benthos and fishes were collected in June, July and September of 2006 and January and February of 2007. Fish were collected with electric fishing techniques and benthos with a surber net. Densities of benthic organisms were expressed as the number of individuals per/m 2. After sampling, the invertebrates were fixed in 90% ethanol, and, in the laboratory, were identified to the lowest taxonomical level. Approximately, seventy individuals from each species were selected randomly in each month. Fishes were fixed in 10% formalin in the field and transferred to 70 o GL ethanol in the laboratory. Fishes had their stomachs removed for subsequent analysis. Fish diet was described according to the numeric frequency method. The Manly Electivity Index was applied in order to verify prey selection. The most abundant families in both benthos and diet of both fish species were the same, indicating that these species consume mainly most abundant prey in the environment. We concluded that prey selection occurs even for preys that had small abundance in the environment. However, it is the availability of the macroinvertebrate resources that determines the major composition of items in diet of fish, demonstrating that the abundance is the factor that most influences the choice of prey.

The present study was carried out in Mato Grosso fluvial system, a costal drainage from Serra do Mar. We analysed the diet and the feeding daily rhythm of Pimelodella lateristriga from samples carried out during 24 hours over a 4 hour fishing interval,