What is "tetra"

n. Any of several species of small South American freshwater fish of the family Characidae, popular in home aquaria.

n. brightly colored tropical freshwater fishes

A tetra is one of several species of small freshwater fish from Africa, Central America and South America belonging to the biological family Characidae and to its former subfamilies Alestidae (the "African tetras") and Lebiasinidae. The Characidae are distinguished from other fish by the presence of a small adipose fin between the dorsal and caudal fins. Many of these, such as the neon tetra (Paracheirodon innesi), are brightly colored and easy to keep in captivity. Consequently, they are extremely popular for home aquaria.

Tetra is no longer a taxonomic, phylogenetic term. It is short for Tetragonopterus, a genus name formerly applied to many of these fish, which is Greek for "square-finned" (literally, four-sided-wing).

Because of the popularity of tetras in the fishkeeping hobby, many unrelated fish are commonly known as tetras, including species from different families. Even vastly different fish may be called tetras. For example, payara (Hydrolycus scomberoides) is occasionally known as the " sabretooth tetra" or "vampire tetra".

Tetras generally have compressed (sometimes deep), fusiform bodies and are typically identifiable by their fins. They ordinarily possess a homocercal caudal fin (a twin-lobbed, or forked, tail fin whose upper and lower lobes are of equal size) and a tall dorsal fin characterized by a short connection to the fish’s body. Additionally, tetras possess a long anal fin stretching from a position just posterior of the dorsal fin and ending on the ventral caudal peduncle, and a small, fleshy adipose fin located dorsally between the dorsal and caudal fins. This adipose fin represents the fourth unpaired fin on the fish (the four unpaired fins include the caudal fin, dorsal fin, anal fin, and adipose fin), lending to the name tetra, which is Greek for four. While this adipose fin is generally considered the distinguishing feature, some tetras (such as the emperor tetras, Nematobrycon palmeri) lack this appendage. Ichthyologists debate the function of the adipose fin, doubting its role in swimming due to its small size and lack of stiffening rays or spines.

Although the list below is sorted by common name, in a number of cases the common name is applied to different species. 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.

Tetra (born October 1999) is a rhesus macaque that was created through a cloning technique called " embryo splitting". She is the first cloned primate, and was created by a team led by Professor Gerald Schatten of the Oregon National Primate Research Center.

Tetra is any of several species of freshwater fish in the family Characidae from Africa, Central America and South America.

Tetra may also refer to:

• Tetra-, a numerical prefix that refers to four
• Tetra (company), a supplier of aquarium equipment and fish food
• Terrestrial Trunked Radio (TETRA), a standard for encrypted radio networks
• Tetra, an alias for Princess Zelda in The Legend of Zelda: The Wind Waker and The Legend of Zelda: Phantom Hourglass
• Tetra Galaxy, the fictional galaxy in the game Metroid Prime Hunters
• Mitsubishi TETRA, a concept car
• Tetra JSC, a Ukrainian company, manufacturer of devices and equipment for searching and measuring of ionizing radiations
• Tetra Pak, a multinational food processing and packaging company of Swedish origin
• Quadriplegia is also known as tetraplegia, shortened to tetra.
• Tetra Tech, an environmental engineering and resource management firm
• Tetra (album) (stylised as Tetr4), the first album from the French break-beat band C2C

Tetra or the Tetra Werke (Company) is a fish food manufacturing company founded by a young German scientist, Dr. Ulrich Baensch.

Tetra (stylised as Tetr4) is the first album from the French break-beat band C2C. It was released on September 3, 2012 off the On And On label. The album reached the top of the French chart from September 3, 2012 to September 9, 2012 and " Down the Road" peaked at 27 on Hot Modern Rock Tracks.