Argonectes is a small genus of characins in the broader piranha and pacu order (Characiformes), found in major river systems of the Amazon and Orinoco basins - the atlas records it from Brazil, Colombia, Peru, and Venezuela. Atlas species range from 10–14 in, giving them a substantially larger build than the small tetras most aquarists associate with the order. They are silvery, streamlined open-water fish, built for life in the main channels and larger tributaries of these river systems rather than in slow backwaters.
This genus is essentially outside the aquarium hobby - its size and open-water schooling habits make it impractical for home aquaria, and data are sparse on either species being kept in captivity at all. A. longiceps, known locally as jatuarana in parts of its Amazonian range, is the better-documented of the two; A. robertsi is known mainly from scientific collections. Conservation status is only partly assessed, with one atlas species Least Concern and the other Not Evaluated.