Black Widow tetra (Gymnocorymbus ternetzi)

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Black Widow tetra

Gymnocorymbus ternetzi5839.JPG
Black Widow tetra

Gymnocorymbus ternetzi

57 Litres (15 US G.)

2.5-5.1cm (1-2 ")




5.8 - 8

20-26.1°C (68 -79 °F)

8-12 °d

1:2 M:F

Pellet Foods
Flake Foods
Live Foods

5-6 years



This animal is available captive bred

Additional names

Black Tetra, Skirt Tetra, Black Skirt Tetra, Butterfly Tetra, Black Widow Tetra, White Skirt Tetra, Petticoat Tetra, Goldskirt Tetra, Strawberry Tetra, Blueberry Tetra

Additional scientific names

Moenkhausia ternetzi, Tetragonopterus ternetzi


Black widow or Skirt tetra is native to Bolivia, Brazil and northern Argentina where it can be found in the middle and upper water layers or river basins.


Females are slightly bigger than males and have a larger belly. Males have a wider anal fin, and a narrower more pointed dorsal fin.

Body Shape and Size: In some tetra species, females tend to be slightly larger and have a rounder body shape, especially when viewed from above. Males may exhibit a more streamlined and slender profile.

Coloration: Sexual dimorphism in coloration is common among tetras. Males may display more vibrant and intense colors compared to females, particularly during the breeding season. Look for differences in the brightness, pattern, or iridescence of their markings.

Fin Differences: Analyzing the fins can provide clues about the sex of tetras. Males may have more elongated or pronounced dorsal and anal fins, especially during the breeding period. Additionally, some species exhibit differences in the shape or size of other fins between males and females.

Egg Spot: In certain tetra species, females may have a small, visible egg spot near the anal fin. This spot mimics the appearance of eggs and plays a role in courtship and breeding behavior. However, not all tetras exhibit this feature.

Behavioral Cues: Observing the behavior of tetras can offer insights into their sex. During the breeding season, males might engage in courtship rituals, such as displaying vibrant colors, fin flaring, and chasing females. Additionally, females may display a rounder abdomen when carrying eggs.

Courtship and Spawning Behavior: Paying attention to courtship and spawning behavior can be a clear indicator of sex. Males often initiate courtship displays, actively pursuing females and participating in elaborate mating rituals.

It's important to note that these guidelines are general and may not be applicable to all tetra species. Some tetras may exhibit minimal sexual dimorphism, making it challenging to differentiate between males and females without careful observation over time. Consulting species-specific literature or seeking advice from experienced aquarists can provide valuable insights for accurately sexing tetra fish in a particular aquarium.

Tank compatibility[edit]

A peaceful community fish that should be kept in groups of 6 or more. Keep with other peaceful community fish, but nothing with long fins as the Black Widow Tetra may nip, especially if kept in small numbers.


Tetra fish are omnivorous and have a diverse diet that includes a combination of both plant and animal matter. In their natural habitat, tetras typically consume small invertebrates, insects, larvae, and various types of aquatic plants.

In captivity, a well-balanced diet for tetra fish can consist of high-quality commercial flakes, pellets, and granules designed for tropical fish. Additionally, providing them with live or frozen foods like brine shrimp, bloodworms, and daphnia enhances their nutritional intake and supports their overall health. Offering a varied diet ensures that tetras receive the essential proteins, vitamins, and minerals necessary for vibrant coloration, growth, and reproductive health in an aquarium setting. Regular feeding, appropriate portion sizes, and maintaining water quality contribute to the well-being of tetra fish in captivity.

Feeding regime[edit]

Feed once or twice a day.

Environment specifics[edit]

Keep in a spacious tank with hiding places amongst plants as well as open swimming space. The tank should be mature and well filtered but without too much current. Avoid very bright lights.


A peaceful active shoaling fish.


Tall, oval-shaped and highly compressed they are noted for their curved anal fin which is quite long. It is almost as long as the entire rear half of the body. Two known true colour variations are available, the most well known being the Black Skirt Tetra which has a silver body colour while the fins are mostly black with two or three vertical bands on the body. The White Skirt Tetra lacks colour and the body is white, almost appearing pink, while the fins are mostly translucent. Long-fin varieties of both colours have been bred but are difficult to keep as they will fin-nip amongst themselves.

Special Notes[edit]

This species is one of those fish that is sometimes offered dyed (Many aquarists consider the dying of fish unethical, please read and understand fish dying before purchasing dyed fish). They are often referred to as Fruit Loop Tetras.
A natural variation of the Black Skirt Tetra is also the Petticoat or White Tetra.
There are also 'painted' versions available. These fish are fed particular highly coloured food which alters their body colour. But they quickly loose this colour when taken home.
Although the term "Glofish" refers to genetically modified Danio rerio, a new selection of genetically modified black skirts called "Glo-Tetra" has now become available in the pet trade.



External links[edit]