Astyanax bagual

Astyanax bagual reaches 7.8 cm (3.1 in) standard length (SL), with a rather compressed body of moderate depth. It has 24-28 branched anal-fin rays, 11–13 pectoral-fin rays, and 7 pelvic-fin rays. The lobes of the caudal fin have either 10 or 11 rays each.There are 37–39 perforated lateral line scales, and 14 scale rows around the caudal peduncle (circumpeduncular scales). There are 2–4 tricuspid maxillary teeth, which can be used as a differentiating feature; similar congeners more often have just one. Its body is largely silver with a slightly darker back and underside, as well as a touch of yellowish or brown on most scales. The dorsal, ventral, pectoral, and adipose fins are all yellow towards the front and red towards the back, and the caudal fin is largely red with a yellowish central portion. The anal fin is mostly yellow with a spot of bright red on the first few rays. A. bagual has two humeral spots, the foremost of which is vertically elongated and wider at the top than the bottom. The second humeral spot is large and sometimes inconspicuous, blending in with a dark lateral stripe, as well as positioned higher than the first (does not extend below the lateral line). The lateral stripe never touches the foremost of the two spots, but always starts at the second, and terminates in a conspicuous blotch of pigment on the caudal peduncle. …

Astyanax bagual is only known from the Taquari-Antas basin of the Rio Jacuí drainage, which is a part of the laguna dos Patos system in the Rio Grande do Sul state of southern Brazil. It is most often found in smaller rivers up to two meters deep with rocky substrate, and seems to prefer areas of moderate riparian vegetation. A. bagual has been collected at altitudes from 179 m to roughly 300 m above sea level. Little is known of A. bagual's diet and interaction with sympatric life, but it is parasitized by Monogenean species Characithecium chascomusensis. The riparian zones in A. bagual's native range include Atlantic forests and natural grasslands; the environment therein faces some survival pressure due to human activity.

The genus name "Astyanax" is an homage to the Greek figure Astyanax, a warrior and the son of Trojan prince Hector. This possibly originates in the armor-like scales of type species Astyanax argentatus, which are plate-like and silver, but the reasoning was not made clear in the original text. The specific name "bagual" is a Tupí-Guaraní word meaning "wild horse", specifically a sexually mature wild stallion with the associated aggressive temperament. This is an allusion to the presence of bony hooks on all fins of mature male A. bagual. Astyanax bagual currently lacks a common name and has no known synonyms.