Composição e estrutura trófica das assembléias de peixes em um trecho do médio rio teles Pires, Mato Grosso, Brasil

Abstract

The Teles Pires River is located in a historically impacted region in the Tapajós River basin, an extended clear water river in Amazonian basin. Fishes are the most conspicuous vertebrates in its waters and have suffered by anthropic impacts. However, studies on the fish fauna in this region remain rare, and knowledge on the composition and determination of the trophic structure is essential to understand the fish assemblages. Thus, the current work aims to determine the composition of the trophic structure, as well as to analyze the attribute of the food web in the fish assemblages, comparing temporal and spatially, along the hydrological cycle in a stretch of rapids in the middle Teles Pires River, Mato Grosso State, Brazil. Individuals were collected using a set of gillnets of different mesh sizes (from 24 to 120mm), in four field trips from July 2008 to May 2009, including the four different hydrological periods. A total of 1385 individuals from 90 species, 16 families and four orders were captured. The order Characiformes and the family Characidae were predominant in biomass and number of individuals. The stomach contents were analyzed from 990 individuals to determine their diet, trophic structure (richness, biomass and number of individuals) of the assemblage and to analyze the attributes of the food web (number of species in the web, total number of links, linkage density and connectance). Trophic categories were defined by the calculation of the Alimentary Index, combining values of frequency of occurrence and volume used to the diet analysis. Fish species were categorized in seven trophic groups. Herbivorous, insectivorous and piscivorous were the most representative in biomass and number of individuals, which consumed autochthonous resources. Analysis on the attributes of the food web showed a low trophic complexity, and temporal and spatial variations were found on the composition and trophic structure of fish assemblages in biomass, number of individuals and attributes of food web. We suppose these variations may be related especially to the changes on the food resources availability, which were abundant in rising and high seasons in downstream of Cachorro rapids, where values of richness, biomass, number of individuals and attributes of food web were considerable higher.