Astyanax aramburui

Astyanax aramburui reaches a maximum of 6.1 cm (2.4 in) SL (standard length). The body is slender, as is the caudal joint, and the head has a short snout and large eye. The maxillary bears a single tooth. The lateral line has 38 to 42 scales, which is a feature that can be used to distinguish A. aramburui from similar congeners. A round or trapezoidal black humeral spot is present above the lateral line. This also can be used to differentiate it from species such as Astyanax powelli, which has two humeral spots in opposition to just one in A. aramburui. The scales are mostly an iridescent silver with touches of yellow, and there is a scattering of dark color cells (chromatophores) on top of the head and body. The sides of the head and the lateral stripe are both plain silver, ending in a black spot on the caudal peduncle. This spot spreads onto the caudal fin itself, which is largely gray with a darker margin. The first rays of the pectoral fins are dark, but the rest of the fin is hyaline (clear), and the pelvic fin is solely hyaline. The dorsal and anal fins bear scattered black color cells.

Sexual dimorphism. Mature males of A. aramburui bear bony hooks on all fins. …

Astyanax aramburui is endemic to Argentina, originally described from the Paraná and Uruguay river systems. Its type locality is part of a relatively extensive section of river, about 50 metres (164 ft) across at its widest, with substrate consisting of mud and clay. Specific locations from whence it has been cited are the Villaguay Creek and Brazo Chico Creek. The river sub-basin in which both creeks are located, the Gualeguay, has relatively high yearly precipitation, averaging 1,311 mm (52 in). Little is known regarding A. aramburui's dietary needs, but many members of Astyanax are adaptable omnivores.

The genus name "Astyanax" originates in Homer's Iliad. Astyanax was a Trojan warrior, and the son of Trojan prince Hector; the reason for the allusion possibly lies in the scales of type species Astyanax argentatus, which are large and armor-like. ("Argentatus" means "silver"). The specific epithet "aramburui" is an allusion to ichthyologist Raúl Arámburu, who founded the first chair of ichthyology in Argentina; this is particularly pertinent because A. aramburui is endemic to the country. In terms of a common name, A. aramburui is one of various small fish species referred to as "Mojarra" in South America. Otherwise, no common names are in wide use by the scientific community.