Basin-scale planning is needed to minimize impacts in mega-diverse rivers

Species of the loricariid genus Hypostomus Lacépède, 1803 from rio Ribeira de Iguape drainage (São Paulo and Paraná States, Brazil) are reviewed. Four species were found in the area: H. agna (Miranda-Ribeiro, 1907), H. ancistroides (Ihering, 1911), H. interruptus (Miranda-Ribeiro, 1918), and a new species H. tapijara. Hypostomus tapijara is distinguished from its congeners inhabiting rio Ribeira de Iguape basin by the presence of well defined large, dark, and roundish spots somewhat homogeneously distributed over body and fins, and by its relatively broad dorsal fin (interradial membranes apparently wider than in examined congeners from coastal Brazilian drainages). A key, descriptions and illustrations are provided for all species.

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New data are presented on the sex chromosomes of the fish species Eigenmannia virescens (Gymnotiformes, Sternopygidae). A new finding, involving the occurrence of ZZ/ZW sex chromosomes, is described in specimens sampled from the São Francisco and Amazon river basins in Brazil. All individuals had a chromosome number of 2n = 38. The homologs of the sex chromosome pair from the São Francisco river basin sample differed only in their morphology, while those from the Amazonian sample differed both in morphology and heterochromatin pattern. A possible model for the evolution of the sex chromosomes in E. virescens is proposed, including data from populations from the Paraná (Brazil) river basin, in which male heterogamety has already been described. The occurrence of different sex chromosome systems in species and populations of the neotropical freshwater fish fauna is discussed.

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Myxiops aphos, new genus and species, is described from a river in the eastern portion of Bahia State, Brazil. Myxiops is distinguished from all other characid genera by the combination of the following features: infraorbitals fused in a unique fashion, resulting always in less than six autogenous bones; a single tooth row in the premaxilla; presence of somewhat pedunculate teeth, expanded and compressed distally, with cusps similar in shape and perfectly aligned along distal margin; ventral margin of toothed portion of maxillary curved towards ventral margin of premaxilla and maxillary teeth forming a continuous series with premaxillary teeth; margins of pre-and postzygapophyses with projections anteriorly and posteriorly directed; accumulation of epithelial cells forming globular structures distributed over head and scales; and base of anal fin without scales covering basal portion of unbranched and anterior branched rays. The presence of these features in other characids is discussed.Myxiops aphos, novo gênero e espécie, é descrita de um rio do leste do Estado da Bahia, Brasil. Myxiops distingue-se de todos os outros gêneros de caracídeos pela seguinte combinação de caracteres: exclusivo modo de fusão dos infraorbitais, resultando em menos de seis ossos autógenos; uma única série de dentes no pré-maxilar; presença de dentes comprimidos com cúspides similares em tamanho e alinhadas ao longo da margem distal dos dentes; margem ventral da porção com dentes do maxilar arqueando-se em direção à margem ventral do pré-maxilar e dentes do maxilar formando um eixo contínuo com os dentes do pré-maxilar; margens das pré-e pós-zigapófises com projeções anterior e posteriormente direcionadas; acúmulo de células epiteliais formando estruturas globulares distribuídas sobre a cabeça e escamas; e base da nadadeira anal sem escamas. A presença destas características em outros caracídeos é discutida.

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As the eyes of environmentalists and researchers focused on the Madeira, Xingu and Tapajós rivers dams, one unknown project to bystanders will negatively affect an entire watershed, causing impacts far greater than any other megadam constructed in Brazil. Despite the environmental modifications, little is known about the UHE Marabá dam and its impacts over such a splendid cellar of species: the Araguaia-Tocantins basin. Historically the Tocantins River is the most impacted amazon tributary, with several already built dams, though the Araguaia River is free of dams. Building the UHE Marabá dam will affect both rivers, and probably extinguish many species increasing the already high number of Amazonian endangered fish species. Due to its unique evolutionary history among Amazonian tributaries, the endemicity found in the basin is probably higher than any other Amazon tributary, as some authors consider it as a different watershed, separated from the Amazon. Describing and foreseeing the impacts locally and globally are the main goals of the present study.