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A tetra is a small, freshwater fish. There are over 150 species of fish known as tetra, though they do not all belong to the same family or genus, and often represent only some members of a family or genus. All tetras, however, belong to the order Characiformes, which also includes the pirhana, among many other types of fish. Tetras are native to parts of Africa and South and Central America.
The name tetra comes from the Greek word for "four," since tetras and other fish of the Characidae family are characterized by their four fins: the caudal, dorsal, anal, and adipose fins. The adipose fin is often considered the distinguishing feature of the tetra, though some species, such as the emperor tetra, do not have an adipose fin. Tetras often feature brightly colored stripes on the side, and there are many different colors available. For example, emperor tetras are a deep purple if kept in the proper lighting conditions, while the Belgian flag tetra features black, red, and yellow stripes. Bloodfin tetras are silver with red fins.
Many tetra species are popular in freshwater aquariums, since they are peaceful, attractive, and relatively easy to care for. Most tetras can live for about five years in captivity. Tetras of different species will often school together in an aquarium, and tetras are a good choice for a community tank since they live peacefully with other kinds of fish. They should not, however, be kept in the same tank with aggressive fish species. In addition, tetras should always be kept in groups of at least five to ten fish, depending on the species, since they are schoolers by nature and can be stressed by living in solitude.
Neon tetras are perhaps the most popular species for aquariums. The brightly colored fish are native to South America, though they are commercially bred in parts of Asia today. Other popular species of tetra for aquariums are also called neon tetras, though they are not closely related. These include green neon tetras, black neon tetras, and cardinal or red neon tetras.