[[ Astyanax Baird & GirardZBK]]
The genus Astyanax Baird & GirardZBK includes more than 100 nominal species (Garutti & Britski, 2000) distributed from southern United States to the Río Negro in Argentina ( Almirón et al., 1997). The genus is diagnosed by the presence of two series of teeth in the premaxilla, the first series with a variable number of teeth and the second series with equal or graduated teeth, usually five in number; crowns of premaxillary and mandibulary teeth usually ridged and denticulated; maxillary with few or no teeth; a complete lateral line; absence of a predorsal spine; and scales present on caudal-fin base. Several of these features are broadly distributed among characid fishes, however, and there are no phylogenetic studies that support monophyly of the genus.
Eight species of AstyanaxZBK are presently considered to occur in northwestern Argentina: A. fasciatus (Cuvier); A. eigenmanniorum (Cope); A. asuncionensis GeryZBK; A. abramis (Jenyns); A. lineatus (Perugia); A. latens Mirande, Aguilera & AzpelicuetaZBK; A. chico Casciotta& AlmironZBK; and A. tumbayaensis Miquelarena & MenniZBK. Of these, only the last three have their type localities within this area. Astyanax fasciatus and A. eigenmanniorum were described from the Río San Francisco basin and Rio Grande do Sul, respectively, both in Brazil (Cuvier, 1819; Cope, 1894), with the latter species subsequently considered to be restricted to the Laguna dos Patos system (Malabarba, 1989). The remaining species were described from the Paraguay and Paraná basins. Several species with anal-fin ray and lateral line scale counts similar to A. eigenmanniorum have been described from Argentina in recent years (e. g. Azpelicueta & García, 2000; Azpelicueta et al., 2002a, 2002b; Almirón et al., 2002; Casciotta & Almirón, 2004; Casciotta et al., 2005; Miquelarena et al., 2005; Miquelarena & Menni, 2005). The purpose of this paper is to describe another species, also similar to A. eigenmanniorum, that is broadly distributed in the upper Río Bermejo basin of northwestern Argentina.