The Penang betta (Betta pugnax), common name Giant betta, is a species of freshwater spiked rayed fish in the gourami family (Osphronemidae) of order Perciformes. It is native to and common in swiftly flowing forest streams of the Malay Peninsula, Cambodia, Thailand, Borneo, and Sumatra, having originally been described from a population in Penang state in Malaysia. In addition to its native range, the species has been introduced to Guam.
The Penang betta grows to a maximum length of 12 inches but its average is 4 in. Preferring clear, soft, acidic waters of 24, this betta shelters among submerged roots and leaves in its native streams. It is one of the mouthbrooding Betta species. B. pugnax, as a natural predator of mosquito larvae, has found use in mosquito control effots. Prior to its being eclipsed in Western public recognition by the mass-imported B. splendens (the Siamese fighting fish), B. pugnax was well known as a fighting fish, attracting the interest of scientists studying animal behaviour at least as long ago as the 1880s. While today far less popular than the ubiquitous B. splendens, the Penang betta is reputed to be easily kept and bred in hobbyist aquaria.
Cantor originally described the Penang betta as Macropodus pugnax, classifying it alongside the paradise fish (M. opercularis); its specific epithet, pugnax, is Latin for "fighting". B. brederi is a junior synonym for this species. B. pugnax is also known as the forest betta, the Malayan betta, and the Penang mouth-brooding fighting fish.