Tetra

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Tetra
Black neon tetra, Hyphessobrycon herbertaxelrodi
Black neon tetra, Hyphessobrycon herbertaxelrodi
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Characiformes
Family: Characidae
Alestiidae
Pristella tetra—Pristella maxillaris.

Tetra is the common name for various small, often colorful, tropical, freshwater fish within the two characiform (order Characiformes) families Characidae—and in particularly its subfamily Tetragonopterinae, the "South American tetras"—and Alestiidae, the "African tetras." The African tetras formerly were classified in Alestiinae as a subfamily of Characidae, and remain within Characidae in some classifications.

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, tetras, add to the wonder of nature for humans. Tetras also are valuable ecologically due to their role in food chains, preying upon smaller invertebrates, such as insects, and being prey for larger fish, mammals, birds, and so forth.

Description

Golden Pristella tetra, a morph of Pristella maxillaris.
Silver tipped tetra—Hasemania nana.

Tetras traditionally were classified within the family Characidae (characins), and in particularly the subfamilies Tetragonopterinae (South American tetras) and Alestiinae (African tetras). However, this family has undergone much taxonomic revision and many authorities have moved the African tetras to the family level, called Alestiidae (Nelson 2006).

Both Characidae and Alestiidae belong to the order Characiformes. Characiformes are characterized by well developed teeth (most are carnivores) and the presence of a pelvic fin (with five to twelve rays) and normally an adipose fin, and a body that is almost always scaled (Nelson 1994).

Characidae is a large and diverse family of freshwater subtropical and tropical fish, with members found in Central and South America, southern North America, and Africa, and include such varied forms as the piranhas, the tetras, a blind cavefish in Mexico (populations of Astyanax mexicanus found in caves) and Brazil (Stygichthys typhlops), and a species found as far northward as southwestern United States (Astyanax mexicanus) (Nelson 1994). The characins are distinguished from other fish by the presence of a small adipose fin between the dorsal fin and caudal fin. Both the Characidae family and the Alestiidae families are comprised only of freshwater fish.

The South American tetras, placed in the subfamily Tetragonopterinae within Characidae, comprise numerous genera, including Hemigrammus, Hyphessobrycon, Paracheirodon (the neon, green, and cardinal tetras), and Tetragonopterus.

The African tetras, now placed in the family Alestiidae, include 18 genera, including Alestes (=Brycinus) and Hydrocynus, with about 110 recognized species in total (Nelson 1994).

Tetra species

The following are some species with the common name of tetra. Though 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.

References
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