The tetra are a variety of species of small freshwater fish, belonging to the family Characidae, which are distinguished by the presence of a small adipose fin between the dorsal and caudal fins.
Tetra is a diminutive term of Tetragonopterus, which comes from the Greek four, and before it was designated to fish, with fins on all four sides, or four fins. Due to the popularity of these fish, many are related to them, including species from other families, which are misnamed tetra, such as the tetra vampire fish.
Tetra fish usually have a compressed body, are fusiform, and can typically be identified by their fins. They have a caudal fin normally, which is bifurcated, and whose upper and lower lobes are the same size; also its dorsal fin is one of its most significant characteristics, because it is a short connection to the body of the fish.