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.
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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