Excreções de peixes amazônicos usando a abordagem da Estequiometria Ecológica e da Teoria Metabólica da Ecologia

Abstract

Fish are important in processes of uptake, transfer and transformation of energy and nutrients in aquatic food webs. Through their excretions, fish supply nutrients for autotroph organisms, representing the main source of nitrogen and phosphorous for primary producers in some fresh water systems. Body size, diet, as well as environment light-nutrient conditions, affect excretion rates and ratios of nutrient recycled by fish. The Amazon basin encompasses the most diverse fish fauna in the world, however nutrient recycling by fish in that ecosystem had never being surveyed so far. The main purpose of this thesis was to assess nitrogen and phosphorus release by fish, measuring their excretions in field conditions. One hundred fifty three incubation experiments were performed using 59 wild caught native species. We used structured equations models in order to measure direct and indirect effects of body size on excretion rates and ratio. Results showed that excretion rates were negatively related to body mass and body stoichiometry, while excreted N:P was positively related to body mass. We could reveal the indirect effect of body mass on excretion because body mass also affects body stoichiometry. In order to identify effects of ontogeny and body stoichiometry on N, P and N:P excretion we used second hand data to create a proxy to growth rate, assuming the fish grow faster as smaller they are from their maximum size, than we compared body stoichiometry and excretion rates and ratios of juvenile in contrast to adult fishes. Results revealed that growth affects body stoichiometry and excretion ratios in the beginning of the juvenile phase. Overall, our conclusions point out that body size, body stoichiometry and growth affect N and P release by fishes.