FISH FEEDING IN BRAZILIAN RESERVOIRS: ALTERATIONS AND CONSEQUENCES IN THE EARLY STAGES OF COLONIZATION.

Abstract

With the increased of dam constructions in Brazilian rivers during the last few decades, it has been necessary to understand their impacts on the fish fauna. Fish feeding behavior is directly associated with the reservoir colonization process. Thus, in this review paper we show the changes in food sources and their use by fish in Brazilian reservoirs during the early stages of colonization. Food allochthonous sources, such as flooded vegetation and terrestrial invertebrates, are quickly used by opportunistic fishes. Availability of autochthonous sources (plants, zooplankton, zoobenthos and fishes) may increase or decrease, changing the fishes diet of different ways. The greatest alterations are the notable increase of zooplankton which is capitalized by filtering fishes, increasing extraordinarily their populations; and the enormous increase of the forage fishes, which usually lead to an increase in abundance of piscivores. These changes affect the trophic structure in the new environment, leading to temporary changes of the food web. However, most studies cited in this review paper were conducted over a short temporal scale. To reach more conclusive answers about the trophic organization of the fish fauna, monitoring programs encompassing middle to long term scales in the impoundments are recommended.