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.
The term tetra is not actually a taxonomic, phylogenetic term. Because of the popularity of tetras in the fishkeeping hobby, many unrelated fish are commonly known as tetras, including species from differing families. Even fish that are vastly different may be called tetras, such as Hydrolycus scomberoides, occasionally known as the Sabretooth Tetra or vampire tetra.
Although the list below is sorted by common name, in a number of cases the common name is applied to different species, depending on country and context. Since the aquarium trade may use a different name for the same species, advanced aquarists tend to use scientific names for the less-common tetras. The list below is incomplete.