Astyanax bagual is a small species of freshwater fish known only from the Taquari-Antas river basin in southern Brazil.

[1] The possibility of more than one unnamed Astyanax species native to the Taquari-Antas river basin, the type locality of A. bagual, was remarked upon in a study of the relevant ichthyofauna in 2013.

[7] Astyanax bagual reaches 7.8 cm (3.1 in) standard length (SL), with a rather compressed body of moderate depth.

[8] 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.

[5] This is an unusual feature within the genus; most other species that display similar dimorphism have hooks restricted to the anal, pelvic, and/or pectoral fins.

[9] 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.

[12] 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.

Construction of the Belo Monte dam, the most prominent power station along its length, radically altered the river's flow.