Description
The black tetra, or black widow tetra, has an unmistakable outline: a tall, compressed body, two dark vertical bars at the front and a rear half, dorsal and anal fins included, washed in black like a skirt.
It is one of the hardiest tetras there is. It comes from subtropical southern waters, so it handles lower temperatures and harder water than Amazonian tetras.
Two things are worth knowing before buying: with age the black fades to silvery grey, and in a small group it tends to nip other fish's fins. Neither is serious if you know beforehand.
Behavior
Active and shoaling. In groups of ten or twelve the energy stays among themselves; with three or four, it spills over onto neighbours as fin nipping.
It lives well with similar-sized, short-finned fish: other sturdy tetras, danios, cherry barbs, corydoras, kribensis.
Avoid housing it with slow, long-finned fish: bettas, pearl or blue gouramis, young angelfish and male guppies.
Habitat
Gymnocorymbus ternetzi lives in the Paraguay and Guaporé basins in Brazil, Bolivia, Paraguay and Argentina: slow rivers, lagoons and backwaters with vegetated banks.
It is a seasonal climate: the water cools in winter, which is why the black tetra copes with a temperate home better than most of its relatives. In the aquarium, plants along the sides and open water in the middle are enough.
Tetra negro is a schooling species, which means that in the wild it lives and moves in large, coordinated groups.
Keep at least 6 individuals so they feel comfortable and their stress level stays low.
Habitats
Fish sharing this habitat
These fish appear in one or more habitats linked to this profile. It doesn't mean they are directly compatible in an aquarium.
Details
🌊 Water parameters
🐠 Minimum tank size
Breeding
A prolific egg scatterer. It spawns among fine plants or moss, and a well-fed pair releases hundreds of eggs.
The parents eat the spawn, so a separate tank with a mesh or dense moss is needed. The fry hatch within a day and start on infusoria before moving to brine shrimp nauplii.
Diet
Omnivorous and voracious, it accepts everything.
- Staple: quality flake or micropellets.
- Supplement: frozen daphnia, brine shrimp and mosquito larvae, twice a week.
Well fed, it nips less: some of the fin biting is hunger, not temperament.
What about your tank?
Enter your tank's values to see only the compatible species that fit them. Litres apply to fish.
Compatible fish
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 6–7 and 22–26 °C.
They share water: pH 6.5–7.5 and 24–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 20–25 °C.
They share water: pH 6.5–7.5 and 20–24 °C.
They share water: pH 7–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 25–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 7.5 and 24–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7.5 and 24–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6–7 and 20–26 °C.
They share water: pH 6.5–7.2 and 22–26 °C.
They share water: pH 6–7.5 and 20–26 °C.
They share water: pH 6–7.5 and 20–22 °C.
They share water: pH 6.5–7.5 and 20–24 °C.
They share water: pH 7–7.5 and 22–26 °C.
They share water: pH 6–7 and 26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6–7 and 22–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 6–6.5 and 24–26 °C.
They share water: pH 6–7 and 23–26 °C.
They share water: pH 6–7.5 and 23–26 °C.
They share water: pH 6–7.5 and 23–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 7–7.5 and 22–26 °C.
Compatible invertebrates
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 7–7.5 and 20–26 °C.
They share water: pH 6–6.5 and 20–24 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 7–7.5 and 20–25 °C.
They share water: pH 7.5 and 24–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7–7.5 and 22–26 °C.
They share water: pH 7–7.5 and 22–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6–6.8 and 20–24 °C.
They share water: pH 6–6.8 and 20–24 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 7–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 7–7.5 and 22–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
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They share water: pH 7–7.5 and 20–26 °C.
Sources
- FishBaseFroese, R. and D. Pauly. Editors. 2026. FishBase. World Wide Web electronic publication.
- Seriously FishSeriously Fish. Gymnocorymbus ternetzi. Ficha de especie; consultada 2026-08.
Plan your next aquarium
Is this fish right for you? Plan a suitable aquarium before setting it up.