EFFECTS OF ENVIRONMENTAL FEATURES ON FISH ASSEMBLAGE STRUCTURES IN THE MACHADO RIVER, AMAZON BASIN, BRAZIL

Abstract

In this study, we examined the influence of the environmental characteristics of three microbasins of the Machado River on the distribution of fish assemblages in order to predict if its fish communities are influenced by abiotic factors. Sampling was conducted in first order streams in the microbasins of the Machado River, state of Rondônia, Brazil. In each stream, we selected two 150 m-long stretches on the main channel. The fish were sampled with different sizes of nets, stored in plastic bags, and taxonomically identified. At each site, the physiochemical parameters of the water (temperature, dissolved oxygen, pH, and electrical conductivity) were measured. Thus, abundance, richness and Hill’s diversity were estimated. The Permutational Multivariate Analysis of Variance (Permanova) was applied to determine the effect in fish abundance, richness and diversity, considering microbasins, physio-chemical water and seasons as explanatory variables. A distance-based redundancy analysis (dbRDA)was performed to determine the influence of physio-chemical properties of the water across the three microbasins and their effect on fish composition. We sampled a total of 6,432 individuals belonging to 4 orders, 19 families, and 56 species. Aequidens tetramerus, Serrapinnus cff. microdon and Serrapinnus aff. notomelas were the most abundant species. Conductivity was the only explanatory variable in which a significant difference was detected for the three response variables. The dbRDA indicated that 44.57% of the total variance was explained by the variables used and were significantly correlated with the abundance and composition of the ichthyofauna (F = 1.88, p = 0.035), conductivity and pH were the most relevant factors. A significant association between fish communities and abiotic factors supports the hypothesis that broad-scale patterns in fish communities in Amazonian small streams are, at least in part, structured by abiotic conditions.