The aim of the present study was to evaluate spatial patterns in composition, structure and distribution of fish assemblages and their relationships with abiotic characteristics in three urban streams of Maringá city, Paraná, Brazil. Fish were collected along the longitudinal gradient by electrofishing in May and November 2004. Temperature, nitrogen, pH, oxygen and phosphorous influenced at most the principal components analysis (PCA). Richness, evenness, Shannon-Wiener index and the first axis of detrended correspondence analysis (DCA) were directly correlated with abiotic characteristics related to chemical urban impact. Species addition prevailed in Miosotis stream sampling stations, and between headwater and intermediary reaches in Nazaré and Mandacarú streams. Replacement occurred between intermediary and lowland reaches of these streams. The dominance of the tolerant species Poecilia reticulata Peters, 1859 indicated the influence of the urban impact on fish assemblages.
Chemical impact; Poecilia reticulata
