Arapaima leptosoma is a species of freshwater fish endemic to Brazil.

Like other members of the genus Arapaima, this fish can breathe air.

It is known only from the confluence of the Solimões and Purus Rivers in Amazonas, Brazil, although due to the lack of obvious geographic barriers, it likely has a larger range.

[1] Live individuals occasionally show up in the aquarium trade, although they are usually misidentified as Arapaima gigas.

[3] It is classified as data deficient by the IUCN Red List due to the lack of information about the population or threats to species.