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The upper Jejuí River is a major tributary of the Paraguay River in eastern Paraguay and is the principal drainage for the Mbaracayú Forest Biosphere Reserve. Despite the international significance of the biosphere reserve and detailed documentation of its terrestrial fauna and flora, the fish fauna in its streams remains relatively unknown, with 48 species previously recorded. We sampled 35 sites within the biosphere reserve over five years (2007–2011) to assess the richness of its ichthyofauna. These surveys yielded a new total of 105 known species for the biosphere reserve, including two newly-recorded orders, Gymnotiformes and Cyprinodontiformes, and 14 newly-recorded families. Fish community composition resembled that of previously-reported fish communities from the Paraguay River drainage, with characiforms and siluriforms comprising the majority of the species (57.1% and 31.4%, respectively). Post hoc analyses showed significantly greater ichthyofaunal diversity at sites within the Mbaracayú Forest Nature Reserve, a core protected forest area within the biosphere reserve, compared to areas outside the nature reserve, suggesting a negative impact from deforestation and land conversion on fish assemblages in these headwater streams. Broad regional deforestation places greater emphasis on important management decisions that will protect current biodiversity. [ABSTRACT FROM AUTHOR]

Aegla are endemic to southern South America and have been documented in Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay. Documentation in Paraguay is sparse, with the last published encounter occurring in 1985; in 1999, the genus was proposed extinct within that country. Since then, a few individual aeglids have been found scattered throughout the Rio Tebicuary watershed. In 2009, aeglids were discovered within the Rio Jejuí watershed within eastern Paraguay; males and ovigerous females were successfully captured including a female carrying more than 20 juveniles beneath its pleon. All individuals from the 2010 field season were later identified morphologically as Aegla platensis Schmitt, 1942. This discovery comes after a two-decade gap in abundant aeglid collections within Paraguay and serves as the first recorded breeding population of aeglid crabs to be documented. [ABSTRACT FROM AUTHOR]