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The black tetra (Gymnocorymbus ternetzi) also known as the black skirt tetra, petticoat tetra, high-fin black skirt tetra, and black widow tetra, is a freshwater fish of the characin family (Characidae). It is native to the Paraguay and Guaporé River basins of southern Brazil, Argentina, and Bolivia.
Growing to about 6 cm (2.5 in) total length, the black tetra has a roughly tetragonal body shape and is greyish in colour, fading from near black at the tail to light at the nose. Two prominent, black, vertical bars appear just posterior to the gills. It is a schooling fish, and requires at least six in a group.
In the aquarium
The black skirt tetra is a common fish that is widely available for purchase. It will live in warm water (26°C or 78°F), but being native to the Rio Paraguay south of the Tropic of Capricorn, it will also tolerate slightly cooler water than some tropical fish. Like most tetras, it is adapted to soft water with a pH between 6.5 and 6.8, with plenty of plants.
The black tetra is an omnivore and will eat most anything it can fit into its mouth. Hobbyists often provide live foods such as daphnia and mosquito larvae, and frozen foods like bloodworms.
The species reaches sexual maturity at about two years of age. It will spawn in water of about 78°F. Like most characins, this species spawns by intermittently releasing and fertilizing eggs among plants. It frequently eats its own eggs, so keepers remove the fish after spawning. The juveniles accept a diet of brine shrimp or commercial powdered fish food.
GloFish black tetras in shades of bright green, orange, purple, and pink are available.