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bonariensis' diet is based on insects, scales, plants and detritus. Microcrustaceans (Cladocera and Copepoda) were the main items, allowing the characterization of the species as zooplanktivore. The species has a superior position and protractible mouth, with small teeth, creating a serrated pattern, uniformly lined side by side. There are many gill rakers, that are long and close together (typical of filtering fishes); the stomach is ill defined and the intestine is short. There was a gradual increase of O. bonariensis' abundance during the period of field study, mainly after the second year of damming. This fact seems to be closely related with the high abundance and availability of zooplankton in the dammed environment, and also with the ability of the species to exploit this resource.Este estudo teve como objetivo analisar a dieta e ecomorfologia trófica de Odontesthes bonariensis, relacionando estes aspectos à abundância da espécie, no ambiente natural e após a formação do reservatório de Salto Caxias, Rio Iguaçu. As coletas foram realizadas antes (de março de 1997 a fevereiro de 1998 -pré-represamento) e após o represamento (de outubro de 1998 a fevereiro de 2001-pós 1 e 2) e os conteúdos estomacais de 218 exemplares foram analisados pelos métodos de ocorrência e volumétrico. A dieta baseou-se em insetos, escamas, vegetais e detritos, sendo que microcrustáceos (Cladocera e Copepoda) foram dominantes, permitindo caracterizar a espécie como zooplanctívora. A espécie possui boca superior e protátil com dentes pequenos, dispostos em fileiras, conferindo-lhes um aspecto serrilhado. Os rastros branquiais são numerosos, longos e próximos entre si (típico de peixe filtrador), o estômago é pouco definido e seu intestino curto. Houve um incremento gradativo na abundância de O. bonariensis, durante o período de coletas, principalmente no segundo ano após o represamento. Este fato parece estar estreitamente relacionado com a elevada abundância e disponibilidade de zooplâncton no ambiente represado e a capacidade da espécie em explorar este recurso.

Studies in Macroecology deal with patterns and processes on large scale (spatial, temporal and taxonomic) and that by definition are too comprehensive to be studied with replicated, manipulative and controlled experiments as it has been traditionally performed in Ecology. Macroecological studies are still conducted with a focus on terrestrial vertebrates and plants, while marine systems and especially freshwater systems remain little explored. The objective of this study is to highlight some advances in the fields of study of aquatic macroecology (spatial patterns of alpha and beta diversity), using fish from Brazilian streams as the object of analysis. By gathering stream fish occurrence information from large scale data sets, we found high total richness in Amazonia, Cerrado and Atlantic Forest, and found on average seven species per sampling unit, with small variation related to the identity of the analyzed biomes. Yet, species composition is distinct between biomes and we found high turnover levels within them. We will guide the reader through possible causes and mechanisms of the identified patterns.