The Siamese fighting fish (Betta splendens) is one of the most popular species of freshwater aquarium fish. It is a member of the gourami family (family Osphronemidae) of order Perciformes, but was formerly classified among the Anabantidae. It is native to the Mekong basin in Southeast Asia.
The natural colouration of B. splendens is a dull green and brown, and the fins of wild specimens are relatively short; brilliantly-coloured and longer-finned varieties have, however, been developed by breeders (see Appearance, below.)
As B. splendens is the Betta species most commonly known to aquarium hobbyists, it is often but imprecisely sold as, and referred to, simply as "betta" (as a common name), particularly in the United States. The name "betta" can, however, also refer to any of the nearly fifty other members of the genus, including the type species, the spotted betta (B. picta). The fish is known as pla-kad in its native Thailand.