Changes in food resources and their utilization by fish assemblages in a large tropical reservoir in South America (Petit-Saut Dam, French Guiana)

The closure of a dam and the following inundation of large areas constitute a major perturbation of the river ecosystem. Under tropical conditions, one of the first constraints imposed on organisms in the new ecosystem is the trophic one. This work aims at determining which feeding strategies are the most successful for the development of fish populations in such a transforming environment. In addition, it will examine the change in food resource used by the assemblages. Soon after the closure of the Pefit-Saut Dam, French Guiana, higher plants and terrestrial invertebrates constitute the main resources for the fish assemblage but resources of aquatic origin subsequently progressively substituted them. Generalists, already numerous in the river, were the most successful in the first stage of reservoir formation. However, over time, specialist species (detritivores, piscivores, invertivores and herbivores) became more important in the assemblage and the trophic structure became more balanced. These results support the hypothesis of greater colonization ability for generalists and of their decline when competition takes place. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.