A new species of Astyanax is described from the arheic system of Río Sucuma, in Catamarca, Northwestern Argentina. The new species is distinguished from its congeners by a combination of characters including the presence of a broad vertical humeral spot, absence of maxillary teeth, and absence of circuli in posterior field of scales. Furthermore, this species is distinguished by the orbital diameter, head length, branched anal-fin rays, perforated lateral-line scales, transverse scales, dentary teeth with abrupt decrease in size. This species is, to date, the single known fish endemic of Río Sucuma basin.Keywords: Arheic system, Characiformes, Cryptic species, Endemic species, Phylogeny. Una nueva especie de Astyanax, se describe del Sistema arreico del Río Sucuma, en Catamarca, Noroeste de Argentina. Esta nueva especie se distingue de sus congéneres por una combinación de caracteres que incluyen la presencia de una gran mancha humeral, verticalmente elongada, ausencia de diente en el maxilar, ausencia de circuli en el campo posterior de las escamas, además se distingue por un ojo relativamente pequeño, longitud de la cabeza, radios ramificados en la aleta anal; escamas perforadas en la línea lateral; escamas transversas; dentario con dientes que decrecen abruptamente. Esta especie es, a la fecha, el único pez endémico para la cuenca de Río Sucuma.

Papiliolebiashatìnne, a new annual-fish species (Cyprinodontiformes: Rivulidae) from Salta, Argentina. -Papiliolebias hatinne sp. n. is described from a temporary pond, 5 km north of Embarcación, in the rio Bermejo basin, Province of Salta, Argentina. Papiliolebias hatinne sp. n. is distinguished from the only congener, P. bitteri, from the rio Paraguay basin, by a combination of characters: 26-28 vertebrae, with 8-10 being precaudal; second proximal radial of anal fin located between vertebrae 9 and 10 or 10 and 11; 1-2 vomerine teeth; an elongation of jaw Suspensorium; first epibranchial somewhat triangular; 7-8 pelvic-fin rays; 12-13 pectoralfin rays; 20-23 caudal-fin rays; males with anal fin turquoise blue, dorsal and caudal fins bluish, pelvic fin blue, and humeral spot metallic bluish green; females without dark dots on flanks. The chromosome formula is 2n= 28, the FN= 36, integrated by two pairs of metacentric, two pairs of submetacentric and ten pairs of subtelocentric chromosomes.