Abstract In the province of Misiones (Argentina), the filling of the Yacyretá Reservoir (Argentina-Paraguay) to its final dimensions in 2011 formed new aquatic ecosystem, e.g., Garupá Stream was converted into a subreservoir. Reports have been made in this stream of adult individuals and spawning of the Family Sciaenidae, excellent colonizers of modified environments. The larvae of this family are morphologically similar, particularly among Pachyurus and Plagioscion species, making taxonomic differentiation difficult. In the present work, sciaenidae larvae were characterized molecularly at the cytochrome c oxidase subunit I gene in order to determine which species use this environment for reproduction. Additionally, genetic distances, Barcode Index Number (BIN) and Automatic Barcode Gap Discovery method (ABGD) were estimated and phylogenetic trees were reconstructed. The results indicated the presence of Plagioscion ternetzi and Pachyurus bonariensis larvae, and for the first time in tributaries of the region, Plagioscion squamosissimus. The incorporation of P. bonariensis and P. squamosissimus to the faunistic assemblage of ichthyoplankton in the Garupá Stream supports better characterization of the species richness of this secondary watercourse modified by the Yacyretá Reservoir, and advancement in our understanding of use of this area for reproduction.

The aim of this work was to characterize the cytogenetic features of the croaker Pachyurus bonariensis (Perciformes, Sciaenidae). Specimens were sampled at three points along the Parana River. Chromosome preparations were obtained by means of cellular suspension from renal tissue. For cytogenetic analysis conventional and differential C and NOR bands staining techniques were applied. We studied 19 individuals of both sexes, from which a diploid number of 48 acrocentric chromosomes was determined (NF=48). There is not evidence of chromosomal sex determination system. NOR banding showed nucleolar organizer regions in pericentromeric regions of a single pair of chromosomes and C banding showed several pericentromeric blocks.

En el presente trabajo se llevo a cabo la primer caracterizacion citogenetica de la corvina Pachyurus bonariensis (Perciformes, Sciaenidae) capturada en tres puntos de muestreo sobre el Rio Parana. Las preparaciones cromosomicas se obtuvieron mediante suspension celular, utilizando tejidos renales y fueron analizadas mediante tecnicas de coloracion convencional y diferenciales (Bandeos C y NOR). Se analizaron 19 ejemplares de ambos sexos a partir de los cuales se pudo determinar un numero cromosomico diploide de 48 cromosomas acrocentricos, sin evidencias de sistemas de determinacion cromosomica del sexo. La tecnica de coloracion argentica mostro regiones organizadoras nucleolares en un solo par de cromosomas y el bandeo C bloques heterocromaticos pericentromericos en varios cromosomas del complemento.