Astyanax clavitaeniatus is a small species of freshwater fish native to various rivers in the Amazon basin.

Its markings - including a humeral spot and two vertical brown bars - indicate that it is a part of a species complex centered around congener Astyanax bimaculatus.

[4] (Species in the A. bimaculatus group often share elements of pattern and coloration, including A. clavitaeniatus, but can further be linked by genetic evidence, such as chromosomal makeup.

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.

[8] Astyanax clavitaeniatus reaches roughly 7.2 cm (2.8 in) standard length (SL, without the tail fin included).

[3] 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.

[3] The presence of bony hooks on some fins is not an uncommon dimorphism in species of Astyanax, but they are rare in other members of the family Characidae.

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.