Betta raja is a species of betta endemic to the island of Sumatra in Indonesia. It is an inhabitant of swamps in lowland forests. This species grows to a length of 6.4 centimetres (2.5 in) SL. It is used as bait by local fishermen and has also been found in the aquarium trade. Despite its scientific epithet "raja" meaning "Prince" or "king", this species is not identical to the aquarium breed - the King betta.