Originally thought to be restricted to the Tocantins-Araguaia river system, a study in 2012 expanded its range to include the Rio Xingu, as well.

Visually, it bears similarities to other species also within the complex, including reddish fins and a dark humeral spot, but its most distinguishing feature is a black lateral stripe with bright-silver edges.

[5] It is unlikely, however, that A. argyrimarginatus is synonymous with any known species; it can be identified strongly and without confusion through genetic information, using a technique known as DNA barcoding.

The reason for this allusion was not made clear in the nominal text, but it may originate in the scales of type species Astyanax argentatus, which are large and silver, like armor or a shield.

[2] In terms of a common name, A. argyrimarginatus is one of many species of small fish sometimes referred to as "lambari" in South America.

[7] There are 42–46 scales in the lateral line, 27–31 rays in the anal fin, and a single tooth in the maxillary bone; the premaxilla sports multiple multicuspid teeth.

Some congeners demonstrate more dramatic instances of sexual dimorphism, such as A. aramburui; mature males therein bear the same bony hooks, but they also grow small fleshy protrusions on the head and scales.

Other members of the genus are generally adaptable omnivores, and are not shy of allochthonous material;[13][14] this may remain the case for A. argyrimarginatus, but specifics are sparse.

One project with notable impact on the Xingu as a whole is the Belo Monte dam, which radically altered the flow of the river upon construction.