Tetra are species of small South American freshwater fish, belonging to the family Characidae and to its former subfamilies Alestiidae (the "African tetras") and Lebiasinidae. The characidae are distinguished from other fish by the presence of a small adipose fin between the dorsal fin and caudal fin. Many of these, such as the neon tetra, are brightly colored and easy to keep in captivity, and extremely popular for home aquaria.

Taken from WikipediA