Composição da ictiofauna de três afluentes do rio Urubu, Médio Amazonas, Brasil

Abstract

The Amazon basin is the largest hydrographic basin in the world, presenting the largest and most diverse fauna of freshwater fish. However, due to its complex fluvial system and the relatively small number of studies carried out in its waters, mainly in drainage basins of black water rivers, several species are still not known by science, and their fauna is not yet fully defined. Structural elements of the environment, physical-chemical factors of the water and the temporal variation structure fish assemblages interfering in the population dynamics of the species. A positive longitudinal gradient of richness and abundance of fish is expected along the rivers, as well as changes in the composition of their assemblies at different times and between different bodies of water. Considering the lack of information in several places in the Amazon, this work aims to evaluate the composition and distribution of fish species along the Anebá, Carú and Sanabani rivers, characterizing their longitudinal distribution in two periods of the seasonal cycle (rising waters and flooded), through of two collections in three different areas of each river, using seine, traps and gill nets. In each sample unit, the species richness values were determined, being compared through analysis of variance (ANOVA) and Student T test. In order to summarize the similarity patterns of the fish assemblage in relation to the sampling sites, the composition and abundance were evaluated with Non-Metric Multidimensional Scaling (NMDS) and Cluster analysis using the Bray-Curtis quantitative index as a measure of similarity. Permutational Multivariate Analysis of Variance (PERMANOVA) tests were applied to verify the existence of significant differences (p <0.05) in the composition of the ichthyofauna between the three rivers, between the regions of each river and between the periods of collection. The results show 147 species, distributed in 35 families and 10 orders, being predominant the Characiformes, Siluriformes and Cichliformes, having as most representative families Characidae and Cichlidae. The most abundant species were composed of small individuals (Hemigrammus analis, Hemigrammus levis, Hemigrammus melanochrous, Anchoviella guianensis, and Hemigrammus bellottii) representing 56.42% of the individuals captured. An order (Gobiiformes), five families (Bryconidae, Poeciliidae, Prochilodontidae, Trichomycteridae, Triportheidae) and 60 species (two new for science), had no record in the Urubu River basin. The tests carried out indicate an increase in the richness and abundance of fish upstream of each river and a difference in the composition of the ichthyofauna of the three rivers, of the three regions of each river and between the two collection periods, indicating the influence of structural elements of the environment. , physico-chemical factors of water and the water cycle in the fish community. The results demonstrate the importance of sampling in different locations and at different times to capture different species of fish that inhabit each region. It is also noteworthy that the larger river regions, formed by the lakes at the mouth of the three rivers with the Urubu river, can be adopted for ichthyofaunistic survey studies, since it is representative of the species composition of the fish assemblage in each River.