Astyanax clavitaeniatus

Astyanax clavitaeniatus reaches roughly 7.2 cm (2.8 in) standard length (SL, without the tail fin included). The body is deep, at least 37.4% the length of the body (but usually deeper), and slightly elongated. The caudal peduncle is thick. The snout, slightly pointed, is equal to or less than the diameter of the eye in length. The dorsal fin is situated at the midpoint of the body, and sports 12 rays (3 branched and 9 unbranched). There are 19 caudal-fin rays, 26–32 anal-fin rays, 8 or 9 pelvic-fin rays, and 12 or 13 pectoral-fin rays. Early studies presented clear morphometric differences between A. clavitaeniatus, A. siapae, and A. rupununi, but more modern understandings recognize a great deal of overlap between the three. The coloration is generally similar to what most species in the A. bimaculatus complex present. Generally, the body ranges from silver to silver-blue or silver-green, with a darker back and paler belly. There is a distinct humeral spot that is rounded or horizontal. Two vertical bars in a dark-brown color are present, with one intersecting the humeral spot and the other 2 or 3 scales behind. In others of the complex, there is often a dark spot on the caudal peduncle that continues onto the fin-rays; A. …

Astyanax clavitaeniatus was originally described from the Surumu river in Roraima, Brazil; paratypes were also collected from the Uraricoera river, in Fazenda Canadá creek and Pau Rocho creek. Other specimens have been collected from the Río Takutu, as well as the Ríos Branco and Negro. All of its habitats are found within the Amazon Basin. Little else has been researched of its ecology, such as diet or behavior. While it is not known to widely share its habitat with other species of Astyanax, it does live in sympatry with A. rupununi and A. bimaculatus in the Río Takutu. Other sympatric species include members of the genera Hemigrammus, Hyphessobrycon, Jupiaba, and Moenkhausia, as well as the tetra Iguanodectes spilurus.

The genus name "Astyanax" is an allusion to the Iliad, though the reason was not made clear in the original text; Astyanax was a warrior of Troy and son of prince Hector. One possibility is that the scales of the type species Astyanax argentatus, which are large and silvery, reminded researchers of armor or a shield, as a warrior might have worn. The species name "clavitaeniatus" comes from Latin, wherein "clava" means "club" and "taenia" means "band" or "stripe", in reference to a dark lateral stripe that gradually thickens towards the tail before tapering off sharply, which results in a club or cudgel shape.