Black Widow Tetra - Gymnocorymbus ternetzi

Black Widow Tetra (Gymnocorymbus ternetzi)

The Black Widow Tetra is a classic and hardy freshwater shoaling fish, recognised by its deep-bodied silver-grey shape, bold black vertical bars and dark flowing anal fin. Also known as the Black Skirt Tetra or Black Tetra, this species is active, adaptable and well suited to mature community aquariums. It is generally peaceful, but because it is lively and can occasionally nip long fins, it is best kept in a proper group with robust, peaceful tank mates rather than slow or delicate species.

Common Name:
Black Widow Tetra. Also commonly referred to as the Black Skirt Tetra, Black Tetra, Petticoat Tetra or Blackamoor Tetra.

Scientific Name (Latin):
Gymnocorymbus ternetzi

Maximum Size:
Around 6–7.5 cm, with mature females usually becoming slightly larger and fuller-bodied than males.

Water Type:
Freshwater

Origin / Natural Habitat:
Native to South America, including the Paraguay and Guaporé River basins, with records extending towards Argentina. In the wild, Black Widow Tetras occupy middle and upper water layers in freshwater habitats where they swim in groups and feed on small invertebrates.

Water Parameters:
Temperature: 20–26°C
pH Range: 6.0–8.0
Hardness: soft to moderately hard water, around 5–19 dH

Temperament:
Generally peaceful, but active and occasionally nippy if kept in too small a group or with unsuitable tank mates. Best kept with other confident community fish that will not be stressed by its movement or occasional chasing.

Diet:
Omnivorous. In nature, it feeds on worms, small crustaceans and insects. In the aquarium it should be offered a varied diet including quality flake, small pellets, micro granules, frozen daphnia, brineshrimp, cyclops, bloodworm and occasional live foods.

Minimum Tank Size:
A practical recommendation is at least 80–100 litres for a proper group, with a 60 cm aquarium or larger as the minimum and a longer aquarium preferred for more natural swimming behaviour.

Behaviour & Activity:
This is an active mid-to-upper level shoaling fish that should be kept in a group of at least 6, ideally 8–10 or more. In good numbers, Black Widow Tetras are more confident, display better behaviour and are less likely to bother tank mates. They appreciate planted edges, open swimming space, subdued areas and a secure lid, as active tetras may jump when startled.

Aquarium Category:
Community Fish
This species is suitable for a robust peaceful community aquarium. Suitable tank mates include other medium-sized tetras, rasboras, danios, peaceful barbs, Corydoras, bristlenose plecos, dwarf cichlids and other confident non-aggressive fish. Avoid bettas, fancy guppies, long-finned fish, very timid nano fish, aggressive cichlids and large predators.

Special Requirements or Care Notes:
Best kept in a mature, well-filtered aquarium with clean water, stable parameters and regular maintenance. A darker background, planted cover and open swimming space will help show natural behaviour. Keeping this species in too small a group can lead to increased chasing and fin-nipping, so group size is one of the most important care points.

Suitable for:
Beginner to intermediate fishkeepers

Availability:
Common in trade, usually as captive-bred stock

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Please note that Mother Nature is a wonderful thing, and variation in patterns and colours will occur — that is part of the unique beauty of these animals.