Astyanax brevirhinus

Astyanax brevirhinus reaches a maximum of roughly 10.0 cm (3.9 in) TL (total length, with the tail fin included). The holotype specimen was 6.8 cm (2.7 in) SL (standard length, excluding the tail fin). The body is about 2.5 times as long as its depth, which makes for a fairly deep-bodied fish. The snout is notably short. The body is deepest at the point just after the start of the dorsal fin. There are 6 scale rows above, 35 scales in, and 4 scale rows below the lateral line. There are 11 rays in the dorsal fin, and 28 rays in the anal fin. The premaxillary has between three and five teeth on each side, which can help differentiate A. brevirhinus from similar species with fewer teeth, such as Deuterodon burgerai (which was originally placed in Astyanax, and has only two or three teeth in the same position). The body is a base silvery color. There is one humeral blotch, which is either rounded or horizontally elongated, and a dark lateral stripe that meets a blotch of dark pigment on the caudal peduncle. This blotch extends through the median caudal-fin rays. (When preserved in alcohol, the dark lateral band turns silver, and the humeral spot becomes obscured.) The caudal fin is mostly a middling-dark opaque color, while the middle rays are darkened (especially towards the tips). …

Astyanax brevirhinus is endemic to the Jequitinhonha River basin in Brazil. The holotype specimen was collected along the Jequitinhonha valley during the Thayer expedition in 1865–66. Its preferred water parameters appear to be within the pH range of 6.2–7.5, and the temperature range of 23 °C (73 °F); tests with higher water temperatures upon captive specimens have resulted erratic swimming behavior and difficulty staying close to the surface of the water. Observation in laboratory conditions reveals shoaling behavior amongst conspecifics of A. brevirhinus, not uncommon in species of Astyanax (both captive and wild). Otherwise, little has been published of the species' diet or behavior. It is known to live in the same river basin as congener Astyanax turmalinensis, but sympatric behavior has not been observed. Other congeners within a similar general region include Astyanax lacustris, Astyanax jacobinae, and Astyanax epiagos, all from rivers to the northeast of Brazil.

The specific name "brevirhinus" means "short-nosed". This is in reference to the particularly short snout that helps differentiate A. brevirhinus from its congeners. The genus name "Astyanax", while slightly less clear, is linked to the Iliad; Astyanax was a Trojan warrior, and son of Prince Hector. The reason for this allusion, while not articulated in the nominal text, is thought to refer to the type species Astyanax argentatus, which has large, silvery scales, like armor or a shield. Astyanax brevirhinus lacks a common name, but "shortsnout astyanax" has been suggested based upon physical traits and the specific epithet.