Inventário da ictiofauna do Ribeirão São João (bacia do Rio Tocantins), Porto Nacional, Tocantins

Abstract

The Neotropical region has a considerable number of aquatic faunal species, where one of the greatest ichthyological diversities on the planet is found. Around 18,300 valid species are from freshwater, of which 20 to 25% are described. Given the taxonomic studies that are carried out, there is an increase in recorded data. The Neotropical Otophysi are represented by the orders Characiformes, Siluriformes and Gymnotiformes and together with the orders Cyprinodontiformes and Cichliformes (Cichlidae) represent more than 70% of the fish richness of the region. The tributaries have great social relevance, enabling the capture of water for public supply, the carrying out of recreational, industrial, agricultural and fishing activities, as well as helping to maintain the environment. However, the objective of the study was to taxonomically identify the fish fauna present in the São João stream, in the municipality of Porto Nacional, Tocantins, which runs within the urban perimeter of the city, located on the right bank of the upper Tocantins river, with the microbasin of area of 82 km². The spring serves as the main source of water collection for the population, is 20 km long and has vegetation typical of the cerrado. During the study, four collections were carried out over a period of one year, from May 2021 to May 2022, with trawl nets and sieves. The material was then screened and identified, with the help of bibliographical references in the area, such as: guides, taxonomic keys, original descriptions and comparison with the ichthyological material deposited in the UNT Ichthyology Laboratory, verifying the identification of scales and teeth, using a stereomicroscope device. After the process, a list of species was prepared, containing name, author, year of description, order and family. In total, 3182 specimens were collected, distributed across 31 species, 15 families and four orders. The percentage was 50% of Characiformes, with the most abundant being 26.7% of Siluriformes, 13.3% of Cichliformes and 10.0% of Gymnotiformes. Ten endemic species were identified, for example Creagrutus britskii, Hemigrammus ataktos e Knodus rufford, probable new species were also analyzed, for example Ancistrus sp. and, the discovery of the new species Rineloricaria quilombola. A specimen was collected Oreochromis niloticus, known as Nile Tilapia, is an indication of human interference in the region, with the addition of exotic species to the natural environment. Therefore, the taxonomic listing became significant, as it brought more real estimates of the biodiversity of the fish present in the tributary, showing there are still many species to be described in the Tocantins-Araguaia basin.