An exploratory survey of fish species inhabiting rapids from the Tocantins-Araguaia River Basin: perspectives on species diversity and conservation

Abstract

Rapid habitats are characterized by an environment of intense hydrologic dynamic, hosting freshwater biodiversity that has adapted to these conditions. Knowledge of the diversity of rapids-dwelling fish is still unsatisfactory in South America’s rivers. Our study surveyed fish species within rapids from the Tocantins-Araguaia River Basin (TARB). We assessed 27 stretches of rapids in different localities along the TARB, using various fishing gears along with free diving, preferably in deeper areas of rocky stretches. Our survey yield 1668 specimens, from 107 species, 79 genera, 28 families, and 10 orders. Among these, 11 species are categorized as being under some threat, according to IUCN and ICMbio. The species Rhynchodoras xingui and Mylesinus paucisquamatus, both listed as threatened at ICMbio, were not recorded during our expeditions in the surveyed area. Baryancistrus longipinnis was only recorded in the Pedral do Lourenço, suggesting a possible distribution retraction. This is the first species surveying focused exclusively on ichthyofauna associated with the rapids of the Tocantins-Araguaia River Basin (TARB). Despite significant alterations in the past four decades, particularly due to the construction of hydroelectric power plants, still house a rich biodiversity. Our results indicate that the remnants of rapids and bedrock habitats in the TARB provide suitable niches for the ichthyofauna, highlighting their importance as potential conservation units.