Abstract This study represents an inventory of fish collected in a first order tributary of the Igarapé Piracolina at Chapada dos Parecis, upper Rio Machado drainage, Rio Madeira basin, Vilhena, Rondônia, Brazil. The sampled stream is located in moderate altitudes (570-590) m above sea level and it is the type locality of five recently described species. Through fieldwork carried out in four fieldtrips between 2014 and 2015, 966 specimens were captured belonging to 18 species, distributed in nine families and four orders. Most of these species have a restricted distribution in the upper Rio Machado. Characidae was the most representative family both in number of species and specimens. One species is recognized as new and endemic to the region, and belong to the genus Pyrrhulina (Lebiasinidae), while five other species (Ancistrus verecundus, Bryconops piracolina, Hyphessobrycon lucenorum, Moenkhausia cambacica, and M. parecis) are also possibly endemic to the upper Rio Machado basin. In this scenario, our results provide relevant data for the establishment of guiding policies, management decisions and bases for conservation actions in moderate altitude areas of the Amazon basin.

Resumo Os peixes registrados aqui foram coletados em quatro igarapés da bacia do alto rio Tapajós. Expedições realizadas em 2011, 2013 e 2014 durante a estação de seca resultaram na coleta de 1.728 indivíduos pertencendo à 22 espécies distribuídas em 11 famílias e cinco ordens. Characidae foi a família com o maior número de espécies e espécimes capturados. As espécies com maior abundância foram Hyphessobrycon melanostichos, H. hexastichos e H. notidanos. Cinco espécies são reconhecidas como novas e quatro como endêmicas da bacia do alto rio Tapajós. Este trabalho representa o primeiro inventário sobre os peixes da região e fornecerá informações valiosas para a conservação da diversidade pouco conhecida de peixes da Chapada dos Parecis, nas cabeceiras da bacia do alto rio Tapajós.

Abstract The fishes herein included were collected in four small streams of the upper rio Tapajós basin. Through fieldwork carried out in 2011, 2013 and 2014 during the low water season 1.728 specimens belonging to 22 species distributed in 11 families, and five orders were captured. Characidae was the most representative family both in number of species and specimens captured. The most abundant species were Hyphessobrycon melanostichos, H. hexastichos, and H. notidanos. Five species are recognized as new, and four as endemic to the upper rio Tapajós basin. This study represents the first fish inventory for the region and will provide valuable information for the conservation of the poorly known diversity of fishes of the Chapada dos Parecis, in the headwaters of the upper rio Tapajós basin.