Three new species of Hyphessobrycon (Characiformes: Characidae) are described from the upper rio Araguaia basin. Hyphessobrycon langeanii n. sp. is distinguished from all congeners by the presence of a well-defined, round humeral spot, a reticulate color pattern, a broad, horizontally-elongate caudal-peduncle blotch, and a relatively wide, faint midlateral dark stripe. Hyphessobrycon eilyos n. sp. is distinguished from all congeners by the absence of humeral and caudal spots; by the presence of numerous dark chromatophores on the lateral surface of the body, intensely concentrated on the ventral region from the pelvic-fin origin to the end of the caudal-fin base, dorsal, adipose, and caudal fins with carmine red pigmentation in life; and the presence of 7-11 maxillary teeth. Hyphessobrycon weitzmanorum n. sp. is distinguished from all congeners by the combination of the possession of two humeral spots and a general dark color pattern. These three new species, along with Creagrutus molinus (Characidae), Apareiodon tigrinus (Parodontidae), Aspidoras velites (Callichthyidae), an undescribed member of the Hypoptopomatinae (Loricariidae), Cnesterodon septentrionalis (Poeciliidae), and Simpsonichthys cholopteryx (Rivulidae), all of which are apparently endemic of the upper rio Araguaia, indicate that this area is a previously unrecognized area of endemism.
Três novas espécies do gênero Hyphessobrycon (Characiformes: Characidae) são descritas para a bacia do alto rio Araguaia. Hyphessobrycon langeanii n.sp. se distingue de seus congêneres pela presença de uma mancha umeral redonda e bem definida, de um padrão reticulado de colorido, de uma mancha no pedúnculo caudal horizontalmente alongada e de uma faixa longitudinal larga e difusa. Hyphessobrycon eilyos n.sp. se distingue de seus congêneres pela ausência de manchas umeral e caudal, pela presença de numerosos cromatóforos escuros nas laterais do corpo, mais concentrado na porção ventral da origem da nadadeira pélvica até o final da base da nadadeira anal, pela cor carmim nas nadadeiras dorsal, adiposa e caudal em exemplares vivos, e pela presença de 7-11 dentes maxilares. Hyphessobrycon weitzmanorum n.sp. se distingue de seus congêneres pela presença de duas manchas umerais, por um padrão geral do corpo escuro. Estas três espécies, em conjunto com Creagrutus molinus (Characidae), Apareiodon tigrinus (Parodontidae), uma espécie não descrita de Hypoptopomatinae (Loricariidae), Aspidoras velites (Callichthyidae), Cnesterodon septentrionalis (Poeciliidae) e Simpsonichthys cholopteyx (Rivulidae), todas as quais aparentemente endêmicas do alto rio Araguaia, indicam que esta área trata-se de uma área de endemismo previamente não reconhecida

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Two new species of Hyphessobrycon, H. ericae and H. wosiackii, are described from the Amazon basin, Brazil. Both new species are distinguished from congeners by the coloration, composed by one humeral blotch merging with an anterior dark band restricted to the anterior portion of the body and the presence of a caudal peduncle blotch. Hyphessobrycon ericae is distinguished from H. wosiackii by presenting a humeral spot vertically elongated, with an overall appearance of an arrow, instead of an anteriorly rounded humeral spot.

The rediscovery of the enigmatic subterranean characiform Stygichthys typhlops is reported almost a half-century after the collection of the holotype, the only specimen previously known. Thirty-four specimens were collected in two shallow hand-dug wells at the region of the type locality, c. 13 km south-west of the town of Jaíba, Minas Gerais, Brazil. These specimens provide new information on the morphology of this species, and for the first time on its life history. The conservation status of S. typhlops is discussed. The species is severely threatened by habitat loss caused by exploitation of the aquifer.

A new species of Moenkhausia is described from Rio Xingu and Rio Tapajós basins, Brazil. The new species is distinguished from its congeners, except from Moenkhausia moisae, by having more scales in the lateral series, 43-47 (v. 23-41 in the remaining congeners). The new species is distinguished from M. moisae by its colour pattern, which consists of a dark midlateral stripe, and an asymmetrical caudal blotch (inconspicuous or faded in specimens from the Rio Arinos) continuous with the midlateral stripe (v. narrow dark midlateral line and conspicuous, regularly rounded and symmetrical blotch not continuous with the midlateral line). The new species is putatively assumed to be mimetic to Jupiaba apenima, in the Rio Xingu and Rio Teles Pires drainages, and to Jupiaba yarina in the Rio Arinos. The two species of Jupiaba are sympatric and remarkably similar in size, general external morphology and colouration to the new species. A small difference occurs in the colouration between the two species of Jupiaba and is also observed in the two respectively sympatric morphotypes of the new species of Moenkhausia. The occurrence of polymorphic Batesian mimicry is therefore discussed for neotropical freshwater fishes.

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Hemiodus iratapuru, a new species of the Hemiodontidae from the Rio Iratapuru, a left bank tributary of the Rio Jari, Amazon Basin, Brazil, is described. The new species is diagnosed from other species of Hemiodus by modifications in the ectopterygoid, tooth form, scale counts, dorsal-fin form and colour pattern. The new species is proposed to be related to the Hemiodus quadrimaculatus species group.