Description of a New Species of Hyphessobrycon (Characiformes: Acestrorhamphidae) from Rio Madeira, a Greatly Impacted Region of the Amazon Rainforest, Apuí, Brazil

A new species of Hyphessobrycon is described from the Rio Acari, Rio Madeira basin, Amazonas, Brazil. The new species can be distinguished from congeners by the presence of six teeth in the inner series of the premaxilla, black pigment in the dorsal-fin rays and interradial membranes, elongated dorsal-fin rays in sexually dimorphic males, and the absence of a dark caudal-peduncle blotch. In life, the new species shows conspicuous sexual dichromatism, adult males being red to orange and females and juveniles pale yellow.