Black Widow Tetra: Feeding, Caretaking and Breeding

Gymnocorymbus ternetzi

Black widow tetra
emptyvi/Wikimedia Commons/CC BY-SA 3.0

Black Widow Tetra: Overview

  • 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: Egg layer
  • 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 it was only available as wild caught, but all specimens sold now are entirely captive bred, leading 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 members 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 varieties with different color as well as long fins have been produced, some of which are artificially colored. Naturally occurring color variations include white and pinkish hued varieties.

In addition, there are a number of pastel colored specimens that have been achieved with dyes. Avoid any fish that may have been artificially colored as they are more susceptible to disease. Contrary to some reports, the process of dying is stressful to the fish and generally shortens its lifespan.

Purchasing these fish only serves to support the practice.

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, it is 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.

Tank Mates

A schooling fish by nature, Black Widow Tetras are best kept in groups of three or more. They make an excellent community fish due to their peaceful nature. 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 an undemanding species that will adapt to a range of conditions, though subdued lighting and neutral colored gravel substrate are 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, you should initially match them 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 and any type of worms, as well as vegetable supplements such as spirulina.

Sexual Differences

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 occasionally have white spots on the caudal fin; they are smaller, have a broader anal fin, and a narrower more pointed dorsal 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. Condition spawning fish, either pairs or groups, with live foods. If live foods are not available, you can substitute frozen live food. This species prefers to scatter their adhesive eggs among vegetation, so provide plenty of fine-leaved plants such as Java Moss or spawning mops. Keep water temperature at 78-80 F in a dimly lit tank. Once spawning has occurred, remove the parents as they will quickly consume the eggs.

Eggs will hatch after approximately one day. Feed the fry freshly hatched brine shrimp, egg yolk, or finely ground flake foods.