In the present study, we describe the diets of the fish assemblages in two streams in the Maringá region of Paraná that are under the influence of different anthropic impacts. We also evaluate how the origin and use of food resources varies temporally and spatially and how the trophic organization of the fish assemblages differs between the two streams. Fish were collected every two months from October 2006 to October 2007 using sieves, seining and closing nets along two 50 m stretches of each stream. We used the volumetric method to analyze the stomach contents of 599 fish belonging to 15 species. We then employed ANOSIM, SIMPER, NMDS and cluster analyses (using the Bray-Curtis index) to examine how different factors (species, stream, sampling site and season) influenced the diets of the assemblages. The dietary analysis revealed a total of 21 types of items consumed, with the most common being detritus and immature Diptera. Spatial factors resulted in differences in diets between the two streams, with detritus representing the material consumed most often in the Morangueiro stream and immature Diptera being the most consumed item in the Queçaba stream. SIMPER analysis indicated a 76.33% dissimilarity between species' diets during the dry and rainy seasons, with detritus, immature Diptera and testate amoebae making the greatest contributions to this differentiation. In the Morangueiro stream, three trophic guilds were found: detritivorous, detritivorous/aquatic insectivorous, and aquatic insectivorous. In Queçaba stream, six trophic guilds were present: detritivorous, benthophagous, aquatic insectivorous, terrestrial insectivorous, herbivorous and carnivorous. Autochthonous items were generally the items most consumed by species, in particularly in the Queçaba stream. In the Morangueiro stream, food items of indeterminate origin were more relevant. The differences in the diets of fish species between the two streams support the conclusion that urbanization causes the disruption of aquatic environments and trophic organization
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