The term tetra is not a formal taxonomic rank, but rather is the common name used for numerous small fish scattered over numerous genera and different families and subfamilies. Because of the popularity of tetras in the fish-keeping hobby, many unrelated fish are commonly known as tetras. Even fish that are vastly different may be called tetras, such as Hydrolycus scomberoides, occasionally known as the sabretooth tetra or vampire tetra, which is placed in the Characinae subfamily within Characidae.
Being small and brightly colored, and often easy to keep in captivity, many tetras, such as the neon tetra, Paracheirodon innesi, are extremely popular for home aquariums. Whether seen in aquariums or in the wild in a clear stream,