Fish, Tanks and Ponds

Fish, Tanks and Ponds
A comprehensive guide to fish

Gymnocorymbus ternetzi

Black widow tetra

Black widow tetra, Gymnocorymbus ternetziBlack widow tetra, Gymnocorymbus ternetzi
Photos by Andy Rapson


Gymnocorymbus: Greek, gymnos = naked + Greek, korymb = summit, cluster of fruits and flowers

General Notes:

There is a completely white aquarium bred morph of this fish which is used in the dyedDyed fish fish trade. Dye in injected in to the fish giving the fish a blue, green or pink colour. None of these are natural and there is a high mortality in fish being dyed. The dye will slowly fade over several weeks too. When asked some dealers will try to mislead customers about these fish by saying they have been fed on a special colour food rather than admit the true nature of the dyeing process. This is of course rubbish, no such food exists.

Black widow tetras are great community fish which is reliably peaceful. Black widow tetras should be kept in a group of at least five individuals. If kept singly they sometimes nip the fins of other fish which have long flowing fins. Provide these fish with a lot of open swimming space which they need due to their lively nature. They don't require any particular type of set up since these fish are very easy to please and will accept a wide range of conditions as long as you avoid extremes.


Wild black widow tetras feed on insects, crustaceans and worms. In captivity they are bold, unfussy feeders. Use a good quality flake food and supplement this with live or frozen food such as bloodworms, daphnia, glass worms and cyclops.


Female black widow tetras are larger and more plump than are the males.


Black widow tetras are one of the easier characins to breed, a well conditioned pair in a 60 litre aquarium which is bare apart from some plants tied in to bunches and a temp of 78F is all that is required. The eggs are scattered over the plants and fertilised as the male chases the female. The parents will eat their eggs if not removed immediately after spawning. The fry can be reared on micro worms, newly hatched brine shrimps or a commercial powdered flake food.

Wild status

The wild populations of black widow tetras have not been evaluated. Almost all specimens offered for sale are captive bred.

Information at a glance

pH: 6 - 8
dGH: 5 - 19
Temperature: 22 - 28°C (72 - 82°F)
Diet: Omnivore
Size: 6cm (2.5in)
Min tank size: 60 litres
Difficulty level: Easy
Aquarium type: Community
Swimming level: Middle

Distribution and habitat

distribution map for Black widow tetra, Gymnocorymbus ternetzi

Origin: South America: Paraguay and Guaporé River basins to Argentina

Habitat: Slow moving rivers and streams with vegetation.


Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Characiformes
Family: Characidae
Genus: Gymnocorymbus
Species: G. ternetzi (Boulenger, 1895)

Common names:
Black widow tetra, Black tetra, Black skirt tetra

Synonyms: Tetragonopterus ternetzi