- Scientific Name: Gymnocorymbus ternetzi
- Other Names: Black Tetra, Black Skirt
- Family: Characidae
- Origin: Rio Paraguay, Rio Guapore, Bolivia
- Adult Size: 2 inches (5.5 cm)
- Social: Peaceful, good community fish
- Lifespan: 5 years
- Tank Level: Mid dweller
- Minimum Tank Size: 10 gallons
- Diet: Omnivore, eats most foods
- Breeding: Egglayer
- Care: Easy
- pH: 5.8 - 8.5
- Hardness: up to 15 dGH
- Temperature: 68-79 F (20-26 C)
Black Widow Tetras originate from the Guapore and Paraguay Rivers in Brazil. Originally only available as wild caught, all specimens sold now are entirely captive bred, which has led to a number of new man-made variations of this popular fish. Additionally, similar species have been described, including; Socolof's Tetra (Gymnocorymbus socolofi) and the False Black Tetra (Gymnocorymbus thayeri). Both of these species are not as frequently available in the aquarium trade, nor are they as popular as the Black Widow Tetra.
One of the best known representatives of the tetra family, the Black Widow Tetra, is easily recognized by the distinctive black dorsal and anal fins, and vertical black stripes on its body. A number of color varieties as well as long finned varieties have been produced, some of which are artificially colored. Among the color variations are naturally occurring white and pinkish hued varieties. In addition there are a number of more pastel colored specimens that have been achieved via dyes. Any fish that may have been artificially colored should be avoided, as they are more susceptible to disease. Contrary to what some report, the process of dying is stressful to the fish, and generally shortens their lifespan. The purchase of such fish only serves to support the disturbing practice of artificially coloring fish.
Once the Black Widow Tetra achieves its mature size at approximately one year, the dark coloration slowly begins to fade to a silvery gray. By the time the fish has reached five years or more in age, they are quite pale in color. They also pale when stressed or ill. Black Widow Tetras remain relatively small, reaching an adult length of approximately two inches. Hybrids, such as the long-finned varieties, tend to be a bit larger.
A schooling fish by nature, Black Widow Tetras are best kept in groups of three or more. Due to their peaceful nature, they make an excellent community fish. Some owners report that they sometimes nip the fins of slower moving fish, particularly those with long flowing fins such as Bettas or Angelfish.
Black Widows are undemanding species that will adapt to a range of conditions. Subdued lighting as well as neutral colored gravel substrate is preferred. They are accustomed to large plants in their natural habitat, and enjoy a well planted aquarium with some open swimming space. Although not demanding about water, they prefer soft acidic water, preferably tannin stained. Ideally they should initially be matched to the water conditions from the supplier, as sudden changes are not healthy.
In nature Black Widow Tetras eat a lot of live foods. However, they readily accept virtually any food, including live, fresh, frozen, freeze dried, or flake foods. For optimal health, provide a variety of foods that include high quality flake foods, brine shrimp, any type of worms, as well as vegetable supplements such as spirulina.
Female Black Widows are generally larger than the males and have a rounder body. In the female the anal fin runs parallel with the vertical black stripe in her abdomen. Males are smaller, have a broader anal fin, and a narrower more pointed dorsal fin. Males occasionally have white spots on the caudal fin.
Black Widow Tetras do not reach sexual maturity until nearly two years of age. Larger males will generally claim a territory that they will guard during spawning periods. Black Widow Tetras may be spawned in groups having a few more males than females, or as pairs. Spawning fish, either pairs or groups, should be well conditioned with live foods. If live foods are not available, frozen live food can be substituted. This species prefers to scatter their adhesive eggs among vegetation. Be sure to provide plenty of fine-leaved plants, such asJava Moss or spawning mops. Water temperature should be 78-80 F and the tank dimly lit. Once spawning has occurred the parents should be removed, as they will quickly consume the eggs.
Eggs will hatch after approximately one day. The fry may be fed freshly hatched brine shrimp, egg yolk, or finely ground flake foods.