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Gymnocorymbus ternetzi

Gymnocorymbus ternetzi
Black Skirt Tetra
The black tetra (Gymnocorymbus ternetzi) also known as the black skirt tetra, high-fin black skirt tetra or black widow tetra is a freshwater fish of the characin family (family Characidae) (which includes all tetras, including the piranha), of order Characiformes. It is native to the Paraguay and Guaporé River basins of southern Brazil, Argentina, and Bolivia.
Growing to about 6 cm 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 6 in a group, but they can also make do with 3-4 tetras per aquarium.
The black widow tetra feeds on small crustaceans, insects, and worms. It will live in warm water, but, coming partly from the Paraquay section of the Rio Paraguay south of the tropic of Capricorn, it will also take slightly cooler water than some tropical fish, and is sometimes kept in unheated aquariums in rooms that do not get cold. This fish, like most tetras, needs soft, acid water, pH 6.5-6.8, with plenty of plants, although it is one of the more adaptable tetras, and is suitable for a community aquarium with a neutral pH, and a temperature of about 24 degrees C. Although not generally aggressive towards other species, avoid slow moving, long finned fish like male Betta splendens with this fish. Black tetras can be violent amongst themselves, with weaker fishes sometimes chased and nipped by their superiors.