Black Skirt Tetra Care Guide: Tank Size, Tank Mates & Breeding

Based on Jan's hands-on keeping experience · Updated September 2026

Also called: Black Tetra, Black Widow Tetra, Black Widow, Skirt Tetra; pale domestic forms are sold as White Skirt Tetras.

Black Skirt Tetra (Gymnocorymbus ternetzi)

Quick answer: Black Skirt Tetras (Gymnocorymbus ternetzi) are hardy, active South American schooling fish that are best kept in a group of at least six, preferably eight to ten or more. They usually reach about 5-6 cm in aquariums, although FishBase records up to 7.5 cm standard length. A tank around 75 cm long and roughly 70 litres / 18-20 US gallons is a much more practical minimum for a proper adult school than a 10-gallon tank. Keep them at about 20-26°C (68-79°F), feed a varied diet, and choose tank mates carefully because this otherwise peaceful tetra can nip long fins.

Scientific nameGymnocorymbus ternetzi

Adult sizeUsually 5-6 cm; up to 7.5 cm SL recorded

Group size6 minimum; 8-10 preferred

TankAbout 75 × 30 cm / ~70 L or larger

Temperature20-26°C (68-79°F)

pHAbout 6.0-8.0

HardnessAbout 5-19 dGH

DietOmnivorous; especially takes small animal foods

Do not judge this tetra by the word “peaceful” alone.

Black Skirts are community fish, but they have a real fin-nipping tendency. A proper school helps keep social chasing inside the group, while slow-moving fish with long fins can still become targets. This matters especially for Bettas, fancy Guppies and long-finned varieties of other species.

Black Skirt Tetra, Black Tetra or Black Widow Tetra?

All of these common names normally refer to the same species, Gymnocorymbus ternetzi. The fish is deep-bodied and laterally compressed, with two strong dark vertical bars behind the gill area and a broad black anal fin that gives the “skirt” appearance.

Young fish are usually darker and more strongly patterned. Adults often become greyer as they age, so some loss of the intense juvenile black colour is normal and does not automatically mean that the fish is ill.

Several domestic forms occur in the aquarium trade:

White Skirt / White Tetra: a pale domestic form of the same species.
Long-fin Black Skirt Tetra: selectively bred for elongated fins; care requirements are otherwise the same.
Fluorescent GloFish Tetras: transgenic lines derived from G. ternetzi. They are biologically the same species for normal husbandry purposes, although their colour is genetically produced rather than a natural wild-type colour.

Natural Range and Habitat

Black Skirt Tetras are native to South America. FishBase places the species in the Paraguay and Guaporé river basins extending toward Argentina, and specialist references describe populations in Brazil, Bolivia and Argentina. They inhabit freshwater systems and occupy mainly the middle and upper parts of the water column.

Correction to the older Aqua-Fish guide

The previous version said that Black Skirts also naturally inhabit the Rio Negro. We could not verify that claim in the current FishBase distribution data, so it has been removed. Their documented range is centered on the Paraguay and Guaporé systems rather than the Amazonian Rio Negro blackwater system.

Small slow-moving creeks, tributaries and streams with overhanging vegetation are typical habitat descriptions. In the aquarium this does not mean the tank must be dark or packed wall-to-wall with plants. A better layout is a combination of planted or shaded areas and plenty of open horizontal swimming space.

How Big Do Black Skirt Tetras Get and How Long Do They Live?

Most aquarium Black Skirts are around 5-6 cm (2-2.4 in) as adults. FishBase records a maximum of 7.5 cm standard length, which excludes the tail fin. Females are often deeper-bodied and visibly larger when mature.

A realistic aquarium lifespan is around 3-6 years under good conditions. Individual fish can fall outside that range, so lifespan should be treated as an expectation rather than an expiry date.

Why size figures differ between websites

Some sources give total length, while scientific references often use standard length, which stops at the base of the tail. A 6 cm aquarium estimate and a 7.5 cm scientific maximum are therefore not necessarily contradictory.

Black Skirt Tetra Tank Size and School Size

The most useful way to plan for Black Skirts is by tank length school size, not litres alone. FishBase recommends groups of five or more and a minimum aquarium length of 60 cm. Seriously Fish recommends a footprint around 75 × 30 cm, roughly 68-70 litres, for a group.

For everyday keeping we prefer a slightly more conservative rule: six fish is the minimum social group, while eight to ten or more usually gives a better display and distributes chasing more naturally.

Tank	Practical recommendation
10 US gal / ~38 L	Too cramped for the adult school we recommend. The problem is limited swimming length as much as water volume.
13-15 US gal / ~50-57 L	Borderline. It can hold a small group, but it leaves little margin for adult body size, social chasing and tank mates.
18-20 US gal / ~68-76 L, preferably a long tank	A practical starting point for a proper school of six to eight adults.
100 L	Better for a larger school and community tank, with more room for open swimming space and compatible tank mates.
200 L	Excellent space for a substantial school, but there is no need to force the tank toward the old article's “30-40 fish” figure.

Horizontal room matters more than height.

The old guide said deep tanks were better than shallow ones. We would reverse that advice. Black Skirts are active mid/upper-water swimmers, so a longer footprint is generally more useful than extra vertical depth.

How to decorate the aquarium

Keep open swimming space across the middle of the tank.
Use taller plants, wood or other structure around the back and sides.
Floating plants can soften strong lighting.
Fine gravel or sand both work; this species does not depend on a particular substrate.
Use reliable filtration with moderate current rather than extreme flow.

Black Skirt Tetra Temperature and Water Parameters

Parameter	Useful range
Temperature	20-26°C (68-79°F)
pH	6.0-8.0
General hardness	5-19 dGH
Ammonia	0 mg/L
Nitrite	0 mg/L

These fish are adaptable, which is one reason they have remained popular for decades. Do not use that adaptability as an excuse for unstable water. A consistent temperature, zero ammonia and nitrite, and regular partial water changes matter more than chasing an exact pH of 7.0.

Behavior: Peaceful Schooling Fish or Fin-Nipper?

The correct answer is both, depending on the situation. Black Skirts are social schooling/shoaling tetras and are usually good community fish, but mild chasing and fin-nipping are real parts of their behavior. It becomes more troublesome when the school is too small, the tank is cramped or slow long-finned fish are available as easy targets.

A larger group lets much of the social interaction happen among Black Skirts themselves. You will often see fish chasing, displaying and briefly sparring without serious injury.

From Aqua-Fish keeping experience

In our tanks these tetras were active, alert fish that reacted quickly to movement around the aquarium. Group interactions and short chases were normal. They were not territorial cichlids, but neither were they passive background fish. This is one reason a proper school and enough swimming room make such a visible difference.

Black Skirt Tetra Tank Mates

Choose tank mates that are peaceful but not excessively slow or delicate, and that share similar temperature and water requirements. Other robust tetras, many Corydoras, suitable rasboras and similar community fish can work well.

Be more cautious with:

Bettas: long fins can invite nipping.
Fancy Guppies: possible, but the flowing tails make them a less reliable match than the old guide implied.
Angelfish and other long-finned cichlids: adult size and fins create a risk in both directions.
Very timid fish: fast Black Skirts can dominate feeding time.
Aggressive cichlids: Black Skirts are not built to compete with territorial bruisers.

Can Black Skirt Tetras live with shrimp?

Adult Amano shrimp and other large robust shrimp may coexist with a well-fed school, but small shrimp and shrimplets are potential food. Black Skirts naturally eat small invertebrates, so no dwarf-shrimp colony should be considered completely safe with them.

What Do Black Skirt Tetras Eat?

FishBase records worms, small crustaceans and insects in the natural diet. Aquarium fish readily accept flakes, small pellets and granules, but dietary variety is worthwhile.

Food	How to use it
Quality flakes / micro-granules	Routine staple
Artemia, Daphnia, Cyclops	Excellent live or frozen variety
Bloodworms / mosquito larvae	Occasional protein-rich food
Plant-containing prepared foods	Useful dietary variety, but the species is not primarily herbivorous

From Aqua-Fish keeping experience: feeding time is not subtle

Our Black Skirts were very fast eaters. Food hitting the surface or water column could trigger an immediate rush and disappear almost instantly. In a mixed community aquarium, watch that slower fish actually receive their share instead of assuming food distributed around the tank reaches everyone.

Feed one or two small meals per day in amounts the fish finish quickly. The old article included a mandatory Sunday fast “to prevent digestive issues”; there is no need to make a weekly fasting day a rule for healthy adult Black Skirts. Avoiding chronic overfeeding is more important.

Male vs. Female Black Skirt Tetra

Mature females are normally larger, deeper-bodied and rounder, especially when carrying eggs. Males tend to be slimmer, somewhat smaller and may appear darker. Fin-shape differences are sometimes used by breeders, but body shape and fullness are generally easier clues in mature fish.

Sexing juveniles is unreliable. If breeding is the goal, condition a group and select obviously mature, well-fed adults rather than trying to identify tiny young fish by fin shape.

How to Breed Black Skirt Tetras

Black Skirts are egg-scattering fish with external fertilization and no parental care. FishBase classifies them as open-water/substrate egg scatterers. Adults will eat eggs, so a separate breeding aquarium gives dramatically better results.

Condition mature adults with a varied diet including small live or frozen foods.
Prepare a separate breeding tank with clean, stable water around 24°C and gentle aeration/filtration.
Protect the eggs with fine-leaved plants, Java moss, spawning mops, marbles or a mesh/grid that lets eggs fall beyond the adults' reach.
Introduce a conditioned pair or selected breeders. Spawning commonly takes place after courtship, often around morning light.
Remove the adults after spawning. They do not guard the eggs and may eat them.
Keep the eggs and larvae stable. Avoid abrupt temperature changes and very strong light or flow.

How many eggs?

The previous Aqua-Fish version said a pair could produce more than 1,000 eggs in one spawning. A controlled developmental study reported roughly 150-200 eggs per female per spawn. Much larger figures exist in hobby literature, but 1,000 should not be presented as a normal expectation.

Black Skirt Tetra Eggs, Hatching Time and Fry

Scientific work gives us unusually good detail for this species. In a controlled study at 24 ± 0.5°C, the eggs hatched after about 20-21 hours. The eggs were roughly 0.98 mm in diameter, spherical and adhesive/demersal. Newly hatched larvae averaged only about 1.44 mm total length.

SpawningEggs are scattered and externally fertilized.

~20-21 hours at 24°CHatching in controlled laboratory conditions.

Day 3 after hatchingThe mouth opens.

Day 3-4Yolk is absorbed and larvae begin active free swimming.

~Day 32Larval development was complete and juveniles had formed in the published study.

This corrects another weakness in the old guide. It stated that eggs hatch within 36 hours at 26°C and that fry are not ready for food until about day seven. Hatching can actually be faster, while the critical point for feeding is when the mouth opens and the fry become free-swimming.

What to feed Black Skirt Tetra fry

The first foods need to be extremely small: infusoria/paramecia, rotifers or a suitable commercial microdiet. As the fry grow, introduce newly hatched Artemia and progressively larger foods. Baby brine shrimp are excellent, but the smallest newly free-swimming larvae may initially need finer prey.

Clean water is crucial. Use gentle sponge filtration and small water changes rather than heavy flow. A large spawn produces a surprisingly heavy feeding and waste load once the fry begin growing.

Health and Common Problems

Black Skirts are hardy, but “hardy” does not mean disease-proof. Ich, fin damage, bacterial problems and fungal infections can appear under the same poor conditions that affect other aquarium fish.

Before treating symptoms, test the water. Ammonia or nitrite, sudden temperature changes, chronic overcrowding or stress from unsuitable tank mates can create exactly the conditions in which disease follows.

Quarantine new fish when practical.
Keep ammonia and nitrite at zero.
Do regular partial water changes.
Do not crowd a full school into a short nano tank.
Watch for persistent fin damage that may be social rather than infectious.

Black Skirt Tetra Frequently Asked Questions

How big do Black Skirt Tetras get?

Most aquarium adults are around 5-6 cm. FishBase records a maximum of 7.5 cm standard length.

How long do Black Skirt Tetras live?

Around 3-6 years is a realistic aquarium expectation with good care, though individual lifespan varies.

How many Black Skirt Tetras should be kept together?

Keep at least six. Eight to ten or more is even better if the tank is large enough, because social behavior is distributed across a proper school.

Can Black Skirt Tetras live in a 10-gallon tank?

We do not recommend a 10-gallon tank as permanent housing for a proper adult school. A longer 18-20 gallon aquarium around 75 cm in length is a much better starting point.

How many Black Skirt Tetras can live in a 20-gallon tank?

A group of about six to eight is a sensible starting point in a standard long 20-gallon aquarium. Exact stocking also depends on filtration, tank dimensions and whether other fish are present.

Are Black Skirt Tetras aggressive?

They are usually community fish, but they chase and may nip fins. Small groups and cramped tanks can make this behavior more troublesome.

What are good Black Skirt Tetra tank mates?

Choose peaceful, active fish of similar size that share the same water range. Avoid very aggressive species and be cautious with slow, long-finned fish such as Bettas and fancy Guppies.

Can Black Skirt Tetras live with shrimp?

Large adult shrimp may coexist, but small shrimp and shrimplets can be eaten. They should not be considered fully shrimp-safe.

What temperature do Black Skirt Tetras need?

About 20-26°C (68-79°F) is the established range. Stable temperature is more important than trying to keep them at the warmest end.

Do Black Skirt Tetras lay eggs?

Yes. They are open-water/substrate egg scatterers with external fertilization. The adults provide no parental care and may eat the eggs.

How long do Black Skirt Tetra eggs take to hatch?

In a published laboratory study they hatched in about 20-21 hours at 24°C. Temperature affects development, so aquarium timing can vary.

How can you tell a male Black Skirt Tetra from a female?

Mature females are generally larger, rounder and deeper-bodied, while males tend to be slimmer and somewhat smaller. Sexing juveniles is much less reliable.

Is a Long-fin Black Skirt Tetra a different species?

No. It is a selectively bred long-fin form of Gymnocorymbus ternetzi and has the same basic water and social requirements.

Black Skirt Tetra Pictures

The large photo collection below is part of the value of the original Aqua-Fish article. It shows the species in different positions, ages and lighting rather than relying on one perfect catalogue photograph.

These Aqua-Fish images may be reused on another website if a direct credit link to Aqua-Fish.Net is included on each page where they are displayed.

Video

Our original Black Skirt Tetra video is still available here: Black Skirt Tetra video (MPEG-1, 640 × 480).

References and further reading

This revision combines Aqua-Fish's own long-term aquarium experience with current biological and specialist sources. See FishBase: Gymnocorymbus ternetzi, Seriously Fish: Black Widow Tetra, Çelik et al. (2012): embryonic and larval development, FishBase reproduction summary, and Fisheries and Oceans Canada: environmental assessment of G. ternetzi lines.

The older Aqua-Fish version also cited Miloslav Michalik, Akvarium Terarium 1982/5; useful firsthand and historical material has been retained where it remained consistent with current knowledge.