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Arapaima gigas (Schinz), the "pirarucu", is one of largest freshwater fish of the Neotropical region, naturally occurring in the Amazon, Essequibo, and Orinoco river basins. Herein, it is first recorded from the Grande River, in the upper Paraná River basin. This record is based on the finding of one dead specimen on the left margin of the Grande River, and in situ observation of juveniles and adults in the river. [ABSTRACT FROM AUTHOR]

Hyphessobrycon langeanii was originally described as endemic to the upper Araguaia river basin, Brazil. However, our analysis of several Hyphessobrycon specimens collected in the Correntes river basin and another tributary of the Itiquira River in Mato Grosso state (both belonging to the Paraguay river basin) reveals the first verified record of H. langeanii from this basin and from the states of Mato Grosso do Sul and Mato Grosso. The objective of this study is to provide a novel record of H. langeanii from the basin of the Paraguay River and from the state of Mato Grosso do Sul. We compare the newly discovered populations with the populations in the Araguaia river basin, and we also provide a brief discussion on the biogeography of this species. [ABSTRACT FROM AUTHOR]

Hypostomus khimaera Tencatt, Zawadzki & Fröehlich, 2014 is a species native to the rio Paraguay basin, but it is recorded here from the upper rio Paraná basin for the first time. Our new record was made in the córrego Mimoso, a tributary of the rio Anhanduí, approximately 180 km from the closest previously reported locality. We are unsure whether the occurrence of this species in the upper rio Paraná basin is a consequence of natural phenomena, such as headwater connection during floods or stream capture, or an artificial introduction. Together with the invasive H. cochliodon Kner, 1854, H. khimaera is the second species of the H. cochliodon group recorded in the upper rio Paraná basin. Here, we provide an updated diagnosis of H. khimaera and highlight the differences in opercle exposition as the easiest way to differentiate it from the syntopic and morphologically similar H. cochliodon. [ABSTRACT FROM AUTHOR]

Ectrepopterus uruguayensis Fowler was recently redescribed, with occurrence in lower tributaries of Río de la Plata and lower Río Uruguay, Uruguay. Herein its occurrence is extended and confirmed to Argentina, arroyo El Molino, in Uruguay Department, Entre Ríos Province, Uruguay drainage. [ABSTRACT FROM AUTHOR]