The ichthyofauna of streams in the upper Purus-Antimary interfluve, with an expansion in the occurrence of Amazonian fish species

Abstract Few studies have investigated the ichthyofauna of streams in the upper Purus River basin, hampering efforts to understand the diversity of these numerous bodies of water. This study presents the first inventory of the ichthyofauna in the upper Purus-Antimary interfluve, southwestern Amazonia. The study was based on data compiled from various sources, including online repositories, scientific articles, and fish collected from four streams in a protected area. We assessed species richness, distribution area, conservation status and anthropogenic threats. The fieldwork study was carried out in four "terra firme" streams in the Purus River basin, with fieldwork conducted during the rainy season in March and November 2017. We identified a total of 92 species, 26 families, and six orders. The order Characiformes exhibited the highest species richness with 42 species, followed by Siluriformes with 34, and Gymnotiformes with 8 species. The Characidae family was the most diverse, with 25 species, followed by Loricariidae with 11 species and Callichthyidae with seven species. The collected fish samples totaled 1,794 individuals representing 58 species, 22 families, and 4 orders. The most abundant species were Knodus smithi with 307 individuals, followed by Chrysobrycon hesperus with 247 and Tyttocharax madeirae with 165. Most species were classified as being of low conservation concern. The study expanded the known extent of occurrence for Anablepsoides hoetmeri to 2,163.777 km2. Our findings underscore the importance of conserving aquatic habitats and riparian vegetation within the upper Purus-Antimary interfluve, given the presence of a rich and restricted ichthyofauna. Furthermore, we highlight the significant risks posed by anthropogenic pressures such as deforestation for pastures, wildfires, and illegal fishing activities.