If you accept more than one species, then the one commonly kept in aquariums should be Arapaima arapaima. A name that maybe should be unaccepted, because animals whose specific epithet is the same than the generic one (Vulpes vulpes, Meles meles, Melolontha melolontha, Galbula galbula, etc) are authomatically designated as the type species of the genus, and the type species should be always the first described one, that in this case would be Arapaima gigas.
Captive breeding is being made in industrial scale since many years ago, overall for supply arapaimas for the market of the fish meat. Also, arapaimas has veen introduced in other continents (overall in Asia) where they devastate native fishes both by predation and competition.
It's atonishing that a species so extremely famous (one of the most famous of all fishes) and so heavily impacted by human threats (overfishing) was not evaluated by IUCN, that already evaluated species like almost unknown minute non-endangered snails from some unaccesible part of Europe, for example.
