Betta /ˈbɛtə/ is a large genus of small, often colorful, freshwater ray-finned fishes in the gourami family (Osphronemidae). By far the best known Betta species, however, is B. splendens, commonly known as the Siamese fighting fish.
Bettas have always been used as fighting fish, bred for their aggressive nature and, later, for their brilliant colors. Bettas are labyrinth fish, meaning they have the ability to breathe oxygen directly from the air or from their gills.
As their nickname suggests, betta fish are quite aggressive, but don’t always require solitary confinement. Male betta fish are territorial and should be kept in separate tanks, but some female betta fish can coexist more comfortably. Neon tetras, minnows and various species of catfish have also been known to cohabitate with bettas. Keep any fish known for nibbling out of a betta’s tank, however, as bettas will bite back.