This research characterized the feeding ecology of the fish community of the upper-middle course of Paraitinga River, located within the Upper Tietê River Basin, a peculiar Atlantic Forest area, regarded as a hotspot for fish conservation. Considering the several anthropogenic modifications, knowledge of the trophic structure might contribute to a better understanding of the factors that maintain the present fish community. Fish were collected with electrofishing equipment at 16 sites with different riparian vegetation, including native forest, secondary forest, pasture, and Eucalyptus, during the dry and rainy season of 2004/2005. Results obtained for 15 species indicated a predominance of insectivores and herbivore-detritivores along the course and an increase of total biomass, specifically of the herbivores-detritivores at the pasture sites, which seemed to be mediated by specific habitat features, which included open canopy, high water speed, and deeper areas. Strategies of resource use indicated that 47% of total combination pairs showed high overlap, but competition seemed to be minimized through low co-occurrence, spatial segregation, and abundance of food resources. Niche width was broad for all species, with no significant differences occurring among sites, seasons, and upper and lower course. With regard to the ongoing modifications in riparian zone conditions in this area, the implications of these findings for regional biodiversity conservation are discussed.

Diet of 364 specimens of the dourado (Salminus maxillosus) was studied monthly at Cachoeira das Emas from November/1996 to May/1998, considered the breeding ground of this and other migrant fishes of Mogi-Guaçu River. Only adults were found at this site, and diet consisted exclusively of fish, with predominance of Leporinus sp. Seasonal variation in feeding activity was highest during some months of the rainy and hot season (September-December), when fish composition and number of prey species consumed also changed. These modifications were primarily attributed to an increase in food availability at the site of study during the rainy season, once most of the migrant species, including small Characidae concentrate there at this time of year. Apparently diet shifts, prey availability and rainfall are intimately related, representing a combination of factors that may account for the observed patterns of resource exploitation.Key words: Salminus maxillosus, feeding, Mogi-Guaçu River, prey availability. A dieta de 364 exemplares do dourado (Salminus maxillosus) foi estudada mensalmente na região denominada Cachoeira das Emas de novembro/1996 a maio/1998, local considerado o lar de reprodução desta e de outras espécies migratórias do Rio Mogi-Guaçu. Foram capturados apenas adultos, sendo a dieta composta exclusivamente por peixes com predominância de Leporinus sp. Foi observada variação sazonal da atividade alimentar, que foi maior na estação quente e chuvosa (setembro a dezembro), época na qual a composição e o número de presas consumidas foram distintas. Essas mudanças foram basicamente atribuídas a um aumento da disponibilidade de presas no local de estudo durante o período chuvoso, visto que a maioria das espécies migratórias, incluindo pequenos Characidae, se concentra aí nessa época. Aparentemente, as mudanças na dieta de S. maxillosus, a disponibilidade de presas e a pluviosidade estão intimamente correlacionadas, representando uma combinação de fatores que explicam os padrões de exploração de recursos aqui observados. RESUMOPalavras-chave: Salminus maxillosus, alimentação, Rio Mogi-Guaçu, disponibilidade de presas.

Aim:This study aimed to assess the spatial and seasonal variation of the water quality and physical habitat characteristics along the upper-middle stretch of the Paraitinga River, a tributary of Tietê River, considering the potential influence of different riparian conditions along the stretch studied. Methods: Sixteen sites with different riparian vegetation, including native forest, secondary forest, pasture, and eucalyptus were sampled during the dry and rainy seasons of 2004/2005, before the damming of the Paraitinga Reservoir. Several physicochemical and habitat parameters were determined and data analyzed in relation to spatial distribution and potential influence of riparian conditions. Results: Water quality parameters were in general within the limits established by CONAMA for Class 2 waters, except for turbidity and total phosphorus. There were seasonal and spatial differences in the limnological parameters along the stretch studied and apparently they were related to point specific influences associated with land use and canopy cover. Habitat characteristics were markedly different between the upper and middle river stretches, especially in relation to depth, width, substrate and canopy cover. Conclusions: Although a direct influence on the observed variables could not be attributed solely to the riparian vegetation, vegetation cover seemed to affect particular stream characteristics. Open pasture and eucalyptus sites were subject to point specific effects that caused phosphorus inputs and higher turbidity and temperature, and showed different morphological features, suggesting that land use at the sub-watershed scale was an important factor affecting stream conditions. Keywords: Paraitinga River; riparian vegetation; longitudinal variation; limnology.Resumo: Objetivo: Este estudo teve como objetivo avaliar a variação espacial e temporal da qualidade da água e as características físicas dos habitats ao longo do trecho médio e alto do Rio Paraitinga, um tributário do Rio Tietê, considerando a possível influência de diferentes condições ripárias ao longo do trecho estudado. Métodos: Foram amostrados dezesseis locais sob diferentes condições ripárias, incluindo floresta nativa, floresta secundária, pasto e eucalipto, durante a estação seca e chuvosa de 2004/2005, previamente ao represamento do reservatório de Paraitinga. Vários parâmetros físicos e químicos da água e do habitat foram registrados e os dados analisados em relação à distribuição espacial e potencial influência das diferentes condições ripárias. Resultados: Os parâmetros de qualidade da água estiveram, em geral, dentro dos limites estabelecidos pelo CONAMA para águas de Classe 2, com exceção de turbidez e fósforo total. Diferenças sazonais e espaciais foram observadas nos parâmetros limnológicos ao longo do trecho estudado, que foram relacionadas à influências pontuais associadas ao uso do solo e à cobertura vegetal. Características do habitat diferiram entre os trechos médio e superior do rio, especialmente em relação à profundida...