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The black tetra (Gymnocorymbus ternetzi) also known as the black skirt 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 light at the nose to near black at the tail. Two prominent black vertical bars appear just posterior of 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 can be readily acquired from aquarium dealers. 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. It can be kept in unheated aquariums in rooms that do not get cold. Like most tetras, it needs soft water with a pH between 6.5 and 6.8, and plenty of plants. It is one of the more adaptable tetras, and can live in a community aquarium with a neutral pH and a temperature of about 24°C (75°F).
Although not generally aggressive towards other species, it has been known to fight with the male Betta splendens. It can also conflict with other individuals of its species, with dominant fish harrying weaker ones.
The black tetra is an omnivore and will eat most anything it can fit into its mouth. Care should be taken that all members of the school receive adequate food. Food items that are too large will be rejected by the fish. Keepers may 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. Keepers sometimes move the breeding fish to a separate tank. 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 are easily reared on a diet of brine shrimp or commercial powdered fish food.
A GloFish black tetra in shades of bright green is available.