TROPHIC STRUCTURE OF ICHTHYOFAUNA IN THE ITAIPU RESERVOIR (RIVER PARANA) DURING ITS FIRST FORMATION YEARS

The Itaipu Reservoir, formed in November 1982, submerged an area of 1, 460 square kilometers in a-151 km extension. Monthly collections from November 1983 to February 1989 were carried out in this environment wi th gill nets of different meshes. The aim of the research work was to evaluate the occupation process of the new environment with special re gard to trophic structure. Combining different analytic methods the fe eding habit of fish (69 species) was undertaken by examining stomachs preserved in 4% formaldehyde. Based on the predominant food in more th an 50% of the diet of each species, nine trophic categories were estab lished: planktivores, benthivores, aquatic insectivores, terrestrial i nsectivores, piscivores, omnivores, ileophagous, detritivores and herb ivores. During the study period piscivores, aquatic insectivores, plan ktivores, benthivores and ileophagous species were the most important in number and biomass. Percentages among categories evaluated by Captu re per Unit Effort (CPUE) showed relevant variations in different zone s of the reservoir and years of collection. Benthivores and detritivor es biomass was larger in the river area whereas planktivores, ileophag ous, piscivores and terrestrial insectivores species biomass was large r in the lacustrine area of the reservoir On the other hand, the numbe r of aquatic insectivorous species increased during the years, whereas herbivores and piscivores species decreased in number.