Archolaemus is a genus of ghost knifefish in the family Apteronotidae, endemic to Brazil. The atlas covers 6 species with a wide size range, from about 6 in up to nearly 19.5 in as adults, sharing the long, tapering, scaleless tail and weak electric organ discharge typical of apteronotid knifefish, which they use to sense their surroundings and communicate in the dim, often sediment-laden water of Brazilian river systems.
Only one species, Blax's longtail knifefish (Archolaemus blax), carries an English common name in the atlas, and the genus has essentially no presence in the aquarium trade — it is known almost entirely from ichthyological survey work rather than fishkeeping literature. The conservation picture is mixed: alongside four Least Concern species and one Data Deficient species, the atlas records a Vulnerable assessment, consistent with a genus confined to a single country and therefore more exposed to localised habitat pressure than wider-ranging Amazonian relatives.