EN
To test the role of riparian ecotones in fish community dynamics three different sites along the Sorraia system, were selected. Each station has been under distinct anthropogenic pressure, and characterized by a mosaic of habitat conditions. Fish were collected by electrofishing from October 1991 to October 1993 using two distinct sampling scales, (50 m and small sectors defined according to discontinuities in the dominant vegetation). The variation in species abundance and distribution was correlated with physical factors. The results showed the preference of barbel and nase for riparian vegetation and greater depth and of roach for zones with macrophytic vegetation and high current velocity. Fish community of the Sorraia system does not exhibit a consistent pattern of temporal variation, what is usually observed in Southern streams of the Iberian Peninsula. This fact is probably related to the landscape disturbance.