Black Skirt Tetra
Gymnocorymbus ternetzi
Hardy deep-bodied shoaler with a dark finBeginner
- Lifespan
- 3-5 years
- Size
- 5-6 cm / 2-2.5 in
- Social needs
- Shoaler; keep 6+ together
- Time
- Low; daily feeding, weekly water change
- Cost
- Low
- Diet
- Omnivore; flakes, pellets, frozen foods
Overview
What is this animal?
- The black skirt tetra is a deep-bodied characin from the Paraguay and Guapore river basins, recognised by its silvery-grey body, twin black bars and dark flowing anal fin.
- Larger and sturdier than most tetras, it is a long-standing community favourite.
- It is hardy and adaptable, tolerating a range of conditions, which makes it beginner-friendly.
- Be wary of dyed or injected colour variants, which raise welfare concerns and often show reduced vitality.
Temperament
- Generally peaceful but semi-active, black skirts can become nippy, especially toward long, flowing fins, when kept in groups that are too small.
- A shoal of six or more diffuses this behaviour and keeps them calmer.
- They suit lively community tanks with similarly sized, robust species and open swimmers.
- Avoid pairing them with slow, long-finned fish such as bettas or fancy guppies, and keep them in numbers to reduce fin-nipping.
A good fit for
- Beginners wanting a hardy, forgiving shoaler
- Active mid-sized community aquariums
- Keepers in areas with variable tap water
- Those who like a bold, contrasting fish
Common mistakes to avoid
- Fin-nipping when kept in too-small groups
- Pairing with slow, long-finned tankmates
- Buying dyed or injected colour variants
- Undersized tanks limiting their active swimming
Enclosure
Minimum 75 litres (20 US gallons) — for a group of 6
Cannot be kept alone. The minimum is 6, and the space above is for that group.
- Keep a shoal of at least six in 75 litres (20 gallons) or more, filtered and heated to 22-27C.
- Their adult size and active swimming call for more horizontal space than tiny tetras, with planted edges and driftwood framing open swimming room.
- They accept a range of soft to moderately hard water but value stability most.
- A well-cycled tank with steady parameters and gentle to moderate flow suits their robust temperament.
Supplies
Setup
- Tank and stand
- Filter
- Heater and thermometer
- Substrate, plants and decor
- Liquid test kit
- Dechlorinator and starter supplies
Ongoing
- Micro-pellet or finely crushed tropical flake
- Frozen daphnia and cyclops
- Frozen or live baby brine shrimp
- Microworm culture (optional, for fry and conditioning)
- Spirulina-based flake
- Fine net for removing leftovers
- Small feeding spoon for accurate pinches
Safe substrate: Inert aquarium gravel · Fine, smooth sand · Aquasoil for planted tanks
Care routine
Daily
- Check temperature and equipment
- Feed
- Head-count and look everyone over
Weekly
- Top up evaporationevery 3 days
- Clean glass and clear algae
- Count the school
- Test the water
- Water change and gravel vacuum
Monthly
- Trim and thin the plantsevery 2 weeks
- Check supplies and reagent dates
- Rinse the filter media
Less often
- Replace chemical filter media (Carbon/Purigen)every 2 months
Vet: Quarterly school and stability review — every 3 months
Top resources for more info
Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-09-19.
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Diet
- Black skirts are unfussy omnivores.
- A quality flake or pellet forms a reliable staple, rotated with frozen or live bloodworm, daphnia and brine shrimp, plus occasional plant-based or algae food for balance.
- Feed small amounts once or twice daily, only what is consumed in a minute or two.
- They eat enthusiastically and can outcompete shy tankmates, so make sure slower feeders also reach the food.
Health
- These are among the more disease-resistant tetras, with most problems traceable to chilling, poor water quality or stress.
- Ich and fin rot are the usual concerns and respond well to corrected conditions and early treatment.
- Long-finned varieties are more prone to fin nipping and damage.
- Quarantine new stock, maintain weekly partial water changes, and avoid dyed or injected colour-variant fish, which carry higher disease and mortality risk.
Is your enclosure big enough?
Is this urgent?
In a fish tank the patient is usually the water. Test before you treat — dosing a healthy tank for a disease it does not have makes things worse.
Go now
Today
Soon
Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.
What it really costs
Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.
Bedding and substrate
Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.
Safe
With a caveat
Never
This is our general list for freshwater fish. We have not built one specific to Tetras yet.
My kit says 0.25 ppm. Is that dangerous?
A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature — each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.
Compare with other animals
The same axes for every animal, side by side — the way the guides are written makes that a fair comparison rather than two articles.
Tetras, side by side
Same axes, same care guides — the honest way to choose between types.
See all Tetras side by side →
