Diapoma is a genus of small, silvery characins native to the subtropical rivers of southern South America, with the atlas's 14 species drawn from Brazil, Argentina, Uruguay, and Paraguay — essentially the Río de la Plata basin and its tributaries. At 1–3 in, these are diminutive schooling fish built along the slender, laterally compressed lines typical of many South American tetras, and they generally inhabit clear, cooler-running streams rather than the warm blackwater habitats associated with many of their Amazonian relatives.
Diapoma is not a well-known genus in the aquarium trade; only a handful of species, such as Diapoma guarani (the Guaraní tetra) and Diapoma pyrrhopteryx (known locally as a lambari), carry documented common names, and most of the other atlas species are of more scientific and biogeographic interest than aquarium interest. Where reported, husbandry needs likely follow the general small-characin pattern of soft, well-oxygenated water and a fine-grained diet, but detailed care information for most Diapoma species is sparse. The IUCN picture is mixed: six species remain Not Evaluated, six are Least Concern, and one each is Near Threatened and Endangered, suggesting a genus whose overall conservation status is still being worked out.