This study investigated the fish fauna of a stream in southeastern Brazil that runs through sugar cane-growing and urban areas that are subject to sewage discharge. It aimed to determine the importance of spatial and environmental factors on fish distributions and to assess the use of fish as indicators of the environmental conditions. A longitudinal pattern of chemical water quality was observed, with more disturbed conditions at the urban sites. Several opportunistic or tolerant and omnivorous species such as Astyanax altiparanae, Poecilia reticulata, and Astyanax fasciatus were numerically abundant at these urban sites, which resulted in a consistent increase in species density and biomass along the stream. Redundancy analysis extracted three axes, identifying a nutrient-productivity gradient associated with different species composition patterns, as also detected by the indicator species analysis. No species could be considered a potential indicator of the agricultural area in the dry season, whereas four different species were judged potential indicators of three urban sites. In order to explain species distribution, variation in species abundance was partitioned into spatial and environmental components. The latter was more important, explaining 25.4% of the variation. We concluded that the fish assemblage of the Guamium stream is undergoing the initial stages of disturbance, with pronounced effects at the urbanized area, but no detectable changes at the sugar cane sites. Therefore, fish assemblages might be used as ecological indicators to detect urban impacts in similar rivers. However, the potential use of fish to diagnose stressors in areas of sugar cane plantations should be complementary to more comprehensive studies aimed at understanding the influence of this crop on freshwater resources.
A fish-based Index of Biotic Integrity (IBI) was adapted for use in a stream of the heavily impacted Piracicaba River basin in southeastern Brazil. The influences of land use (mainly sugar-cane crops) and an urban area on the fish community were investigated at ten sites along a 17 km-long stream during the dry and rainy season. The IBI varied with the season and location along the stream, reflecting differences between the agricultural and urban sites, which were more pronounced during the dry season. The final index was positively correlated with a Habitat Quality Index (dry season) but not with a Water Quality Index. The results can be viewed as a tool for assessing and monitoring the ecological health of streams in this watershed.
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