First introduced into the United States in the 1930s, the Blackskirt Tetra is one of the most popular aquarium fish!

The Black Tetra Gymnocorymbus ternetzi is also known as the Black Widow Tetra or Blackskirt Tetra. It’s a good fish for the beginner because it is very hardy, undemanding, and easily bred. This tetra is a real beauty in a community aquarium. It is very active and fast moving. It can be a fin nipper, however, so it should not be kept with smaller fishes but will do very well in a community tank with larger fishes.

A schooling fish, the Black Tetra will appreciate the company of its own kind. The standard school size for the aquarium is 7 individuals, and they will do well with that many or even more of their own. They like a well-lit tank with dense areas of bunched low vegetation, leaving lots of open areas to swim in. They are hardy at 70° F to 90° F, but are prone to develop ich if kept in colder temperatures.

Potential confusion comes from the fact that this is not the only fish known as a Black Tetra. This fish is not to be confused with its cousin Gymnocorymbus thayeri, which is also called the Black Tetra. The G. thayeri is a shyer fish and not as hardy as the Blackskirt. It is similar in appearance to the Black Widow but lighter with more subtle coloration and lacking the vertical striping. Its anal fin is also more convex than the Blackskirt’s.

Some very nice varieties of the Blackskirt Tetra have been developed as well. A popular variation is theLongfin Blackskirt Tetra. Additionally, some color morphs offer a unique look. These include the White Tetra or Goldenskirt Tetra, which has become very common, and the Colored Skirt Tetra.

For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Characiformes
  • Family: Characidae
  • Genus: Gymnocorymbus
  • Species: ternetzi
Black Tetra – Quick Aquarium Care
  • Aquarist Experience Level: Beginner
  • Size of fish – inches: 2.2 inches (5.51 cm)
  • Minimum Tank Size: 15 gal (57 L)
  • Temperament: Semi-aggressive
  • Aquarium Hardiness: Very Hardy
  • Temperature: 70.0 to 79.0° F (21.1 to 26.1&deg C)
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Habitat: Distribution / Background

The Black Tetra Gymnocorymbus ternetzi was described by Boulenger in 1895. The species is not listed on the IUCN Red List. Other common names it is known by are the Black Widow Tetra and the Blackskirt Tetra.

They are found in South America in Paraguay and Guapore Basins where they inhabit the upper layers of the water, feeding on worms, small crustaceans, and insects  These tetras show a preference for small, slow moving creeks, streams, and tributaries that are well shaded from the forest canopy. Many are captive bred for the aquarium industry.

  • Scientific Name: Gymnocorymbus ternetzi
  • Social Grouping: Groups
  • IUCN Red List: NE – Not Evaluated or not listed


The Blackskirt Tetra is a deep-bodied species and laterally compressed. This fish will reach about 2 1/4 inches (5.5 cm) in the home aquarium but will breed at just 1 1/2 inches. It has a lifespan of about 6 to 7 years. It is distinguished by two vertical stripes and by what appears to be overly developed dorsal and anal fins. These make it appear as if though it has a “skirt,” with most of its mass on the bottom half of the body. The fine black color of the juvenile fades to a gray as it matures.

Various strains of the Blackskirt Tetra have also been developed:

    • Long-finned Varieties
      A long-finned variety, the Blackskirt Hifin Tetra, was first developed in Europe. It is also very popular and readily available. These fish are a bit more difficult to breed than the Blackskirt Tetra, probably because they are highly inbred already. They are also referred to as the Longfin Blackskirt Tetra, Long-fin Black Widow, or Longfinned Black Tetra.

  • Colored Varieties
    Strains in a natural white, pink, and blue have also been developed. Of these, the White Tetra or Goldenskirt Tetra has become very common followed by the Colored Skirt Tetra. These fish are sometimes artificially dyed in various pastel colors and sold as Colored Tetras or under various colored names, such as Blueberry Tetra, Strawberry Tetra, or Rainbow Tetra.
  • Size of fish – inches: 2.2 inches (5.51 cm) – These fish get up to 2 1/4 inches (5.5 cm) but will breed at 1.5 inches.
  • Lifespan: 7 years – They have a life span of about 6 to 7 years.

Fish Keeping Difficulty

The Black Tetra is a hardy fish that is great for the beginning fish keeper. They adapt very well to water condition changes and make a great addition to most community tanks.

  • Aquarium Hardiness: Very Hardy
  • Aquarist Experience Level: Beginner

Foods and Feeding

The Blackskirt Tetras are omnivorous. In the wild they feed primarily on worms, small crustaceans, and insects but in the aquarium they will generally eat all kinds of live, fresh, and flake foods. To keep a good balance give them a high quality flake food everyday. Feed brine shrimp (either live or frozen) or blood worms as a treat.

  • Diet Type: Omnivore
  • Flake Food: Yes
  • Tablet / Pellet: Yes
  • Live foods (fishes, shrimps, worms): Some of Diet
  • Vegetable Food: Some of Diet
  • Meaty Food: Some of Diet
  • Feeding Frequency: Several feedings per day – Offer only what they can consume in 3 minutes or less with multiple feedings per day.

Aquarium Care

The Black Tetra is easy to care for providing the water is kept clean. Aquariums are closed systems, and regardless of size, all need some maintenance. Over time, decomposing organic matter, nitrates, and phosphate build up and the water hardness increases due to evaporation. To combat these ever-changing conditions, water should be replaced on a regular basis. At least 25 to 50% of the tank water should be replaced every other week, especially if the tank is densely stocked.

  • Water Changes: Bi-weekly

Aquarium Setup

Because they are very active swimmers, Black Tetras should be kept in a tank at least 20 inches long and ideally 15 or more gallons. They like a soft, peat-filtered water. These fish prefer some plant cover and a darker gravel substrate, but  they also need open areas to swim freely. Additionally, the tank should be securely covered as these fish are skilled jumpers and will probably do so if given the opportunity. 

To get the best out of this fish, set up a biotype tank. For the substrate, use a river sand with some drift wood and twisted roots. Add some dried leaves to the sand, which will stain the water a light brown, and replace the leaves every few weeks. Dim lighting will develop the Black Tetra’s coloring to best effect.

  • Minimum Tank Size: 15 gal (57 L) – Fifteen gallons is the smallest size advisable to keep a small school.
  • Suitable for Nano Tank: Yes
  • Substrate Type: Any
  • Lighting Needs: Moderate – normal lighting
  • Temperature: 70.0 to 79.0° F (21.1 to 26.1&deg C)
  • Breeding Temperature: 82.0° F – These fish will spawn at 82 to 86° F (27.8 to 30° C).
  • Range ph: 5.8-8.5
  • Hardness Range: 3 – 30 dGH
  • Brackish: No
  • Water Movement: Moderate
  • Water Region: All – These fish will swim in all areas of the aquarium.

Social Behaviors

The Black Tetra is an active fish and can be a semi-aggressive fin nipper. Fin nipping can be discouraged by keeping them in schools of at least 8 or more individuals. In large groups, they will focus on each other rather than on smaller fish. They should be kept in a community aquarium with fish the same size or larger. With age, they become more sedentary. These tetras do well with most livebearers, danios, rasboras, other tetras, peaceful bottom dwellers, and some dwarf cichlids.

  • Venomous: No
  • Temperament: Semi-aggressive – Relative to other tetras, Black Tetras have a tendency to be slightly more aggressive. Fin nipping is not uncommon among this species.
  • Compatible with:
    • Same species – conspecifics: Yes
    • Peaceful fish (): Monitor – Watch for stress in other fish caused by Black Tetra fin nipping.
    • Semi-Aggressive (): Threat
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Threat
    • Large Aggressive, Predatory (): Threat
    • Threat – Tetras will out compete them for food.
    • Shrimps, Crabs, Snails: Safe – not aggressive
    • Plants: Safe

Sex: Sexual differences

The male’s dorsal fin is more narrowed and pointed than the female’s. Also, the male’s frontal portion of the “skirt” or anal fin is noticeably broad while the female’s “skirt” tends to run parallel to the stomach line. A mature female is also plumper.

Breeding / Reproduction

The Black Tetra has been bred in captivity, various strains have also been developed, including a long-fin variety and a number of colored varieties. These egg layers are easily bred with a good pairing or in groups containing about 6 individuals of each sex. Black Tetras are ideal candidates for the beginning aquarist interested in a breeding project.

For the best success, females should be conditioned separately from the males for 7 to 10 days prior to spawning. Feed them plenty of small, live foods and frozen foods. Provide a planted, 10 to 20 gallon breeding tank with a small, air-powered sponge filter for filtration and aeration. The breeding tank should be a few degrees higher in temperature than the main tank, at around 82 to 86° F (27.8 to 30° C), with a pH on the acidic side of neutral and a water hardness below 15 dGH. Keep the tank dimly lit with clumps of spawning mops or java moss, which will also give the female a place to deposit the adhesive eggs. A layer of mesh also works if it is wide enough for eggs to pass through but small enough to keep parents out.

The males will chase the females through the plants, occasionally quivering. The females will lay 500 or more eggs in a 2 to 3 hour period. Once a successful spawn has been achieved, remove the parents, or they will eat the eggs. Any eggs that are unfertilized will soon start to look fuzzy as they develop a fungal growth. These should be removed to prevent fungus from spreading to healthy, fertilized eggs. Fry will hatch in approximately 18 to 36 hours and become free-swimming a few days later.

For the first few days, feed the fry infusoria-type foods until they can feed on microworm or brine shrimp nauplii. The biggest challenge is that the young are prone to starving to death if they can’t find a food source in the dark tank. Give the fry plenty of light, both day and night, until they are large enough to eat freshly hatched brine shrimp. See Breeding Freshwater Fish: Characins for a general description of breeding processes, and see Fish Food for Fry for information about types of foods for raising the young.

  • Ease of Breeding: Easy

Fish Diseases

As with most fish, the Black Tetra are prone to skin flukes, parasitic infestations (protozoa, worms, etc.), ichthyobodo infection, parasitic infestations (protozoa, worms, etc.), bacterial infections (general), and bacterial disease. Black Tetra are extremely hardy, and disease is not usually a problem in a well-maintained aquarium. That being said, there is no guarantee that you won’t have to deal with health problems or disease. Remember anything you add to your tank can introduce disease. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so as not to upset the balance.

A good thing about Black Tetra is that due to their resilience, an outbreak of disease can often be limited to just one or a few fishes if dealt with at an early stage. When keeping more sensitive types of fish, it is common for all fishes to be infected even before the first warning signs can be noticed. The best way to proactively prevent disease is to give your Black Tetra the proper environment and a well-balanced diet.

The more closely their environment resembles their natural habitat, the less stress the fish will have, making them healthier and happier. It is recommended to read up on the common tank diseases. Knowing the signs of common tank diseases and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.


The Black Tetra, also sold as the Blackskirt Tetra or Black Widow, is readily available and inexpensive.