Product Details

Black Widow Tetra – Gymnocorymbus ternetzi

The Black Widow Tetra is a hardy, deep-bodied South American tetra with bold dark fins, a silver body and classic black skirt-like markings. Also known as the Black Skirt Tetra, Gymnocorymbus ternetzi is a reliable choice for peaceful community aquariums, provided it is kept in a proper group. It is active, adaptable and beginner-friendly, but it can become nippy if kept in small numbers or mixed with slow long-finned tank mates.

Key Identification:

Common Name: Black Widow Tetra
Other Names: Black Skirt Tetra, Black Tetra, Petticoat Tetra, Blackamoor Tetra
Scientific Name: Gymnocorymbus ternetzi
Fish Type: Tetra / Characin
Water Type: Freshwater

Natural Range & Habitat:

Gymnocorymbus ternetzi is native to South America, where it is recorded from the Paraguay and Guaporé River basins through to Argentina. In the wild, it occupies freshwater habitats where adults are usually found in the middle and upper water layers.

In the aquarium, it does well in planted setups with open swimming space, shaded areas and gentle to moderate water movement. Floating plants, darker décor and planted edges can help the fish feel secure while leaving enough room for group movement.

Appearance & Adult Size:

Black Widow Tetras have a deep, laterally compressed body with a silver to grey base colour, dark vertical shoulder bars and a blackish anal fin that gives the fish its “skirt” appearance. Young fish are usually darker and more strongly marked, while mature adults may become paler or more silvery with age.

Adults usually reach around 5–7 cm, with females often fuller-bodied and slightly larger than males. Males are usually slimmer and may show more defined fin shape.

Aquarium Suitability:

This is a hardy and adaptable community tetra for mature tropical aquariums. Black Widow Tetras suit planted community tanks, mixed tetra displays and peaceful South American-style aquariums. They are more robust than very small tetras, so they can work well with other medium-sized peaceful fish.

They are not ideal for tiny nano aquariums, very shy species, delicate long-finned fish, male bettas, fancy guppies or slow fancy varieties that may attract fin-nipping.

Recommended Aquarium Size:

A practical minimum is 75 litres for a group, with a tank length of at least 60 cm recommended. Larger aquariums of 90–120 litres or more are better for larger groups and mixed community setups.

Keep in a group of at least 6, with 8 or more preferred. A larger shoal helps reduce chasing, improves confidence and keeps most social interaction within the group.

Water Conditions:

Temperature: 20–26°C
pH: 6.0–8.0
Hardness: Soft to moderately hard
Additional Notes: Black Widow Tetras are adaptable if water quality is stable. Keep ammonia and nitrite at zero, maintain low nitrate and avoid sudden water-chemistry changes. They do not need extreme blackwater conditions, but they appreciate clean water, plant cover and some shaded areas.

Temperament & Tank Mates:

Aquarium Category: Community Fish

Black Widow Tetras are peaceful community fish when kept correctly, but they are active and may nip fins if kept in too small a group. Suitable tank mates include other medium peaceful tetras, rasboras, danios, peaceful barbs, Cory-type catfish, bristlenose plecs, dwarf cichlids, rainbowfish and calm livebearers in compatible water.

Avoid male bettas, fancy guppies, angelfish with extended fins, long-finned gouramis, very shy nano fish and slow fancy fish. Keep them in a group so their energy is directed toward natural shoaling and mild in-group bickering rather than tank mates.

Feeding:

Black Widow Tetras are easy-feeding omnivores. Offer quality flakes, small granules or micro pellets as the staple diet. Supplement with frozen or live foods such as daphnia, cyclops, brineshrimp, mosquito larvae and small bloodworm. Occasional vegetable-based or spirulina foods can be included for balance.

Feed small amounts that are eaten quickly. A varied diet helps maintain condition, colour and activity.

Behaviour in the Aquarium:

This species usually swims in the middle and upper areas of the aquarium. It is active but not overly frantic, often moving in a loose group rather than a tight school. Some chasing, displaying and bickering is normal, especially between mature individuals.

Black Widow Tetras are egg scatterers and do not provide parental care. If spawning occurs in a community tank, eggs and fry are usually eaten unless a separate breeding setup is used.

Care Notes:

Add Black Widow Tetras only to a mature, fully cycled aquarium. Keep them in a proper shoal, provide open swimming space and avoid slow long-finned tank mates. They are hardy, but still require regular water changes, good filtration and stable conditions.

Long-finned and pale colour forms are sometimes sold under related trade names. Avoid artificially dyed varieties, as dyeing is harmful and should not be supported.

Recommended For:

Beginner to intermediate

Availability:

Common / Usually captive-bred

Image Disclaimer:

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Natural variation in size, body colour, fin colour, bar intensity and markings can occur between individual fish.