Impacts of Flow Regulation on Mediterranean Freshwater Fishes: Ecological and Biological Deviations in Permanent and Temporary River Systems

River regulation modifies flow patterns, disturbing the bio-ecology of freshwater fishes. In this study we identified which hydrologic variables are more affected by two types of regulation, for hydroelectricity/derivation and agriculture, and analyzed their effects on fishes from, respectively, permanent and temporary Mediterranean rivers at three distinct levels: assemblage composition, food resources and diet, and life-cycles. The derivation dam affected flood related variables, reducing the magnitude and frequency of peak flows. The agricultural dam caused an inversion of the hydrological cycle of typical temporary streams, releasing water in the summer that reduced the magnitude and duration of droughts. In the permanent system, regulation affected fluvial specialists, benefiting the generalist ones, and created a homogeneous community with less intra-annual variation. In the temporary system, regulation benefited the introduced, generalist and tolerant species. Both types of flow regulation had similar effects on food resources, fish diet and life-cycles, reflected on an intra-annual stabilization of resources availability and fish diet, with a higher consumption of plants and detritus, and a decrease of growth rates, condition and reproductive activity. Findings from this study are important to understand the bio-ecological derivation imposed by regulated rivers and to be used as guidelines for flow requirements implementations.