Tetragonopterus is a genus of deep-bodied, silvery tetras in the family Characidae, widespread across river systems of northern and central South America; the atlas's 14 species are recorded from Brazil, Suriname, Venezuela, Colombia, French Guiana, Guyana, Argentina, and Bolivia. At roughly 2.5–5 in, these are mid-sized schooling characins with the classic laterally compressed, silver-flanked tetra body plan. Tetragonopterus is historically significant within the family: it is one of the older described genera in the characin group, and its name has lent itself to the broader term 'tetra' used loosely today for countless unrelated small characins in the aquarium hobby.
Despite that historical prominence, most living Tetragonopterus species are not common in the aquarium trade today; only a couple, such as Tetragonopterus argenteus (the silver tetra) and Tetragonopterus chalceus (the brass tetra), carry established common names and occasional hobby recognition, while the rest of the 14 atlas species are known mainly from regional ichthyological surveys. Where kept, they behave as typical robust, active schooling characins, generally undemanding on water chemistry. Conservation data for the genus is thin: ten of the fourteen atlas species are still Not Evaluated, with the remaining four assessed Least Concern, so while nothing currently points to alarm, most of the genus has not been formally reviewed.