Pestimating fish production in the itaipu reservoir (Brazil): The relationship between fish trophic guilds, limnology, and application of morphoedaphic index

Many experimental studies contributed to the development of the theory of the lacustrine food web, disclosing the important paper of the fish, for decades ignored by the limnology. This work is based on the hypothesis of the trophic cascade relations, particularly related to bottom-up and top-down effect in Itaipu Reservoir (Brazil). Using the made data available by Itaipu Binacional, from 1999 to 2004, analyses of multiple regressions were accomplished to determine the relationships of the dependent and independent variables. A negative effect was verified between the water transparency in relation to suspended solids and turbidity. The chlorophyll-a presented positive relationship with total nitrogen. The omnivorous, detritivorous, and insectivorous fishes presented a negative effect (control) in the cyanobacteria concentrations and chlorophyll-a. The estimate of the production of fish in the reservoir was better related with the concentrations of cyanobacterias of the reservoir. The top-down and bottom-up effect had been confirmed, the forces top-down had been found only in the first trophic level, and the others presented bottom-up effect.