The black skirt tetra is a common fish that can be readily acquired from aquarium dealers. It will live in
warm water (78 degrees F or 26 degrees C), 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.
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.
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 (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 6 in a group, but they can also make do with 3-4 tetras per aquarium.
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The black widow tetra feeds on small crustaceans, insects, and worms.
The black tetra is an omnivore and will eat nearly anything it can fit into its mouth, but care must be taken to ensure that all members of the school receive adequate food.
If the food is too large, the tetra will lose interest and leave it to sink and decay, so the size of the food particles must be appropriate.
It is best to keep a school of 6 black tetras in a medium tank. The Black Tetra will benefit from the occasional feeding with live foods like daphnia and mosquito larvae, and from frozen foods like blood worms.
The black widow tetra reaches sexual maturity at about two years of age. They will spawn in water 78 degrees F.
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A separate spawning tank, heavily planted and at least 15 gallons, is recommended. Like most characins, black tetras spawn by intermittently releasing and fertilizing eggs among the plants.
These fish are frequent egg-eaters and must be removed after spawning. The young are easy to raise, subsisting on newly hatched brine shrimp or powdered processed foods.
The black widow tetra is also known as the blackamoor, blackskirt, black widow, butterfly tetra, or petticoat tetra. The black phantom tetra, Hyphessobrycon megalopterus, is a distinct species.
Note that the black neon tetra Hyphessobrycon herbertaxelrodi is sometimes also called the black tetra.
source : http://en.wikipedia.org/wiki/Gymnocorymbus_ternetzi