Black Skirt Tetra Care Guide

The black skirt tetra is a hardy, deep-bodied, cool-tolerant schooler with a dramatic black 'skirt' of dorsal and anal fin — a genuine beginner fish with two catches a buyer must understand: it is an occasional fin-nipper that needs a big shoal and the right neighbours, and it is one of the most heavily abused species in the dyeing trade. The single most important sourcing rule for this fish: never buy the artificially dyed 'fruit', 'tropical', 'color' or 'blueberry/strawberry' tetras.

Black Skirt Tetra at a glance

The sourced figures the welfare engine uses to judge Black Skirt Tetra — the parseable key facts.

Where it comes from

Black skirts come from the Paraguay and Guaporé River basins down to northeast Argentina — south-central Brazil's Pantanal, Bolivia, Paraguay — small, slow-moving creeks and streams with dense overhanging vegetation, occupying the middle and upper water layers. The southern, subtropical reach (to about 30°S) is the key to its care: FishBase records the wild species across 20-26 °C, pH 6.0-8.0, dH 5-19, a notably wider, more neutral-to-slightly-alkaline envelope than the blackwater neon or cardinal. That is why it reads as 'hardy', does not need soft acidic water, and tolerates the cool end down to about 20 °C — a good option for a low-heat community. The vegetated-creek origin is why it wants planted cover with open mid-water swimming lanes.

Did you know?

• A 130-year-old hobby classic, described by Boulenger in 1895 as Tetragonopterus ternetzi — one of the longest-established aquarium tetras.
• The black 'skirt' fades with age: the dramatic dark dorsal and anal fin and dark rear body dull to silvery-grey as the fish gets older, so an old black skirt can look like a paler, different fish entirely.
• It is one of the world's first GM pets. The black skirt was turned into the 'GloFish Tetra' using fluorescent-protein genes from jellyfish and sea coral (the technology traces to Dr Zhiyuan Gong's team at the National University of Singapore around 1999); GloFish was later commercialised by Yorktown Technologies and bought by Spectrum Brands in May 2017, with trademarked colours such as Starfire Red, Electric Green and Cosmic Blue.
• The same GM fish is legal in most of the USA but contraband in the EU: the FDA cleared GloFish in December 2003, California banned them in 2003 then lifted the ban in 2015, and the European Union prohibits their import, sale and possession. The fluorescence is hereditary, but the licence forbids breeding and selling the offspring.
• Unlike the soft-warm-water cardinal or neon, the black skirt is a neutral-pH, cool-tolerant (down to about 20 °C) subtropical fish — a good unheated-community tetra.
• IUCN Least Concern (assessed 2021), abundant and 'highly commercial' in the trade.

Tank size — and why

A 20 US gallon long with roughly a 60 cm footprint is the practical floor, with bigger better; 15 gallons is a bare minimum for a minimal school only. The real driver is not bioload but group size and swimming room — the whole strategy for keeping this fish peaceful is a large shoal in a long tank, and a bigger footprint is what lets you keep ten to twelve fish so the pecking-order aggression disperses and fins stay intact. Prioritise length over height for the active mid-water school. This is a deep-bodied, fairly tall fish (taller than it is long), so it looks bigger than a slim tetra of the same length; a lid is sensible.

As a guide, a 20-gallon tank comfortably suits about 6–8 Black Skirt Tetra as a single-species display, leaving room for tankmates.

How big does it really get?

Full-grown Black Skirt Tetra reach about 6 cm (2.4 in) long, but they are usually sold at only about 2.5 cm (1 in) — a typical shop size (estimate). At full size, Black Skirt Tetra needs roughly a 20-gallon tank, about 76 cm long; a common 10-gallon starter kit is only about 51 cm.

Adult size is sourced; the shop size is a typical-juvenile estimate; tank length is approximate for a standard 20-gallon aquarium.

Water parameters in practice

Forgiving and adaptable. The primary-source comfort band is 20-26 °C, though the species clearly tolerates the upper 70s to low 80s °F in hobby practice, so a ceiling around 27-28 °C is defensible; the low end of 20 °C is what makes it a usable unheated-tank tetra. On chemistry it is near-neutral and undemanding — sources cluster at pH 6.0-7.5 with FishBase extending to 8.0, and it handles moderately hard tap water happily, so there is no need to chase soft acidic blackwater (save that for breeding). Seriously Fish sums it up: 'not very demanding as far as water quality goes... recommended to the freshwater beginner.' As always, a cycled, stable tank with regular water changes matters more than a perfect number.

Diet & feeding

An omnivorous micro-predator — in the wild worms, small crustaceans and insects. In the tank a good-quality flake, granule or micro-pellet makes the base and it readily takes dry food, topped up with small live or frozen foods such as bloodworm, daphnia and brine shrimp for condition and breeding colour. Feed small amounts once or twice a day and don't overfeed. It is an active, competitive mid-to-upper-water feeder that gets to the surface fast — sometimes too fast for shyer tankmates, which is one more reason to pair it carefully.

Gear & setup

A heater (unless running a deliberately cool tank), a filter giving gentle turnover (a slow-creek species — avoid strong current), sand or fine gravel, and a planted layout with dense edges and overhanging or floating cover that mimics the vegetated creek, plus open mid-water swimming room. Dark substrate deepens the colour. An active upper-water swimmer, so keep it covered.

Temperament & behaviour

Generally peaceful within a proper large school, but a genuine, well-documented occasional fin-nipper — not a myth. AquariumStoreDepot puts it bluntly: 'They are fin nippers and that is not negotiable.' The behaviour is driven by an internal pecking order, and the honest framing is situational rather than vicious: Seriously Fish notes the reputation 'can usually be rectified by keeping it in a small shoal of at least 12 specimens.' A larger group spreads the dominant fish's aggression across many individuals and redirects nipping inward, among themselves, rather than at tankmates' fins. Kept as two or three, they become the worst nippers. The practical consequence is that long-finned and slow community fish — bettas, angelfish, fancy guppies and fancy gouramis — are the classic disaster: their trailing fins are an irresistible target, which is why those species are vetoed from this fish's recommended tankmates regardless of what a coarse size-and-temperament match might suggest.

Group & social needs

An obligate shoaler with a pecking order. Six is the FishBase floor, but the welfare-safe target is much higher: Seriously Fish explicitly says at least 12, and hobby guides say 8-10+, specifically to contain the nipping. Sell yourself on ten to twelve or more, especially for the long-finned strain, and treat six as a bare minimum, not a goal — kept too few, the black skirt becomes a bully. Females are larger and rounder; males are slimmer and smaller with a more pointed dorsal fin.

Compatible tank mates (preview)

A short, engine-cleared shortlist — the species TankStocking's welfare engine clears with Black Skirt Tetra and that suit its size and temperament best. Tap any to load the pairing in the planner.

• Amano Shrimp — Peaceful temperament, similar adult size.
• Bamboo Shrimp (Wood/Fan Shrimp) — Peaceful temperament, similar adult size.
• Black Neon Tetra — Peaceful temperament, similar adult size.

One caveat on the shrimp and snails here: engine-cleared means a size, temperament and water-needs fit — it is not a guarantee of safety. An individual Black Skirt Tetra may still hunt shrimp or pick at small snails, and temperament varies from fish to fish, so add invertebrates cautiously, give them cover, and watch the first encounters.

This engine-cleared shortlist is Black Skirt Tetra's tankmate surface for now — a dedicated tank-mates guide can follow for high-demand species.

Breeding & sexing

Sexing is straightforward in condition: females are noticeably larger and rounder (egg-filled), males slimmer with a more pointed dorsal and a differently shaped anal fin. Breeding is easy-to-moderate — among the more readily bred egg-scattering tetras. Use a separate spawning tank (~10 gal) with fine-leaved plants, a spawning mop or Java moss to catch the eggs, slightly softer, warmer, more acidic water, and condition the pair on live and frozen foods first. They are egg-scatterers that eat their own eggs, so remove the adults straight after spawning; eggs hatch in roughly 18-36 hours, fry free-swimming a few days later, raised on infusoria then microworm and baby brine shrimp. Note that GloFish strains can interbreed, but intentional breeding or sale of GloFish offspring is prohibited by licence.

Lifespan

Three to five years in a well-maintained tank, with six or more achievable on stable water and a varied diet; sexual maturity takes about two years. What shortens it is unstable water, too small a group (chronic stress), and — most dramatically — artificial dyeing, which one care guide reports cuts lifespan 'from the species' normal 3 to 5 years down to 6 to 18 months in most cases' (a single-source figure, treated as approximate).

Common mistakes

• Keeping too few. Two or three black skirts become the worst nippers; buy ten to twelve or more and treat six as a bare minimum, not a goal.
• Mixing with long-finned or slow fish — bettas, angelfish, fancy guppies and fancy gouramis get their fins shredded. This is the single most common compatibility mistake, and why those species are excluded from this fish's recommended tankmates outright even when a simple size match would clear them.
• Buying the long-finned ('high-fin') strain in a small group — it is more vulnerable to nipping by its own schoolmates and should always be kept in a group of eight or more for that reason.
• Expecting permanent jet-black colour. Normal black skirts fade to grey with age — that is a trait, not a defect or an illness.
• THE big one — buying dyed 'painted', 'fruit', 'tropical' or 'color' tetras. These are standard (usually white skirt) tetras chemically bleached and injected with dye; the practice strips the slime coat, causes puncture wounds and immune suppression, the colour fades within months, and lifespan collapses to roughly 6-18 months. Reputable stores refuse to stock them; buying them funds the abuse. Never buy dyed fish.

Signs of trouble

• Persistent colour loss beyond normal age-fade, with clamped fins and hiding — chronic stress, often from too small a group or poor water.
• Frayed or nipped fins — usually intra-group nipping in an undersized school, which can lead to secondary fin rot.
• White spots with flashing or scratching — ich, typically after a chill or unstable water.
• A fish being singled out and relentlessly chased rather than briefly squabbled with — a sign the school is too small to diffuse the pecking order.

Is this fish right for you?

Don't buy black skirts if you can't house a group of ten to twelve in a 20-gallon-plus long, if your tank centres on bettas, angelfish or other long-finned or slow showpieces, or if the only stock available is dyed 'fruit/color' tetras — walk away. On stock quality, prefer standard, leucistic White Skirt, or GloFish stock from reputable sellers. GloFish are genetically modified, not dyed: the fluorescence is hereditary and harmless and they are NOT the welfare problem that dyed fish are — but note the legal restrictions below.

Bringing one home

Add black skirts only to a cycled, stable tank, acclimating gently to match temperature and chemistry before netting them across, and quarantine new stock. If you are mixing them into an existing community, add the full shoal at once and avoid introducing them to a tank built around long-finned or slow showpieces.

Common questions

Are black skirt tetras fin nippers?

Yes — they are a genuine occasional fin-nipper, not a myth ('they are fin nippers and that is not negotiable'). The behaviour is situational, driven by a pecking order, and is contained by keeping a large shoal of 10-12 or more so the nipping is redirected inward rather than at tankmates' fins. Kept as two or three, they become the worst nippers.

Can black skirt tetras live with bettas, angelfish or guppies?

No. Long-finned and slow fish — bettas, angelfish, fancy guppies and fancy gouramis — are the classic disaster: their trailing fins are an irresistible nipping target and they can't escape. This is the number-one compatibility mistake for the species, so those fish are excluded from its recommended tankmates.

Should I buy dyed, 'fruit' or 'color' tetras?

Never. 'Fruit', 'tropical', 'color' and 'blueberry/strawberry' tetras are standard tetras chemically bleached and injected with dye — the colour fades within months, the process strips the slime coat and suppresses the immune system, and lifespan drops to roughly 6-18 months. Reputable stores refuse to stock them, and buying them funds the abuse.

Are GloFish the same as dyed tetras?

No — GloFish are genetically modified, not dyed. The fluorescence comes from inserted jellyfish and coral genes, is hereditary and harmless, and is a completely different thing from the welfare abuse of dyeing. Note, though, that GloFish are legal across most of the USA but banned in the EU, and the licence forbids breeding and selling their offspring.

How many black skirt tetras should I keep?

Ten to twelve or more is the real target — Seriously Fish recommends at least 12 specifically to contain the fin-nipping. Six is a bare minimum, not a goal, and the long-finned strain needs at least eight because it is more vulnerable to nipping by its own school.

Why is my black skirt tetra turning grey?

That is normal age-fade. The dramatic black skirt and dark rear body naturally dull to silvery-grey as the fish ages — it is a trait, not an illness. Persistent colour loss combined with clamped fins, hiding or frayed fins is the version to worry about.

What temperature do black skirt tetras need?

The primary-source comfort band is 20-26 °C, and the species tolerates the upper 70s to low 80s °F in practice. The low end of about 20 °C makes it a good cool-water or unheated-community tetra, unlike the warmth-loving cardinal.

Sources & confidence

Sources & confidence (9 species)

These back the Black Skirt Tetra figures and the previewed tank mates above. Each figure is read from the TankStocking species database (v2026.06); below is the care reference behind it and how confident we are in that data. Confidence reflects the source quality, not whether any pairing is safe. Full source list and the welfare model are on the methodology page.

• Black Skirt Tetra Gymnocorymbus ternetzi — Seriously Fish (seriouslyfish.com/species/gymnocorymbus-ternetzi) high confidence
• Amano Shrimp Caridina multidentata — Aquarium Co-Op amano shrimp care; Aquadiction high confidence
• Bamboo Shrimp (Wood/Fan Shrimp) Atyopsis moluccensis — Aquariadise (aquariadise.com/caresheet-bamboo-shrimp-atyopsis-moluccensis) high confidence
• Black Neon Tetra Hyphessobrycon herbertaxelrodi — Seriously Fish / Aqua-Fish (Hyphessobrycon herbertaxelrodi) high confidence
• Black Phantom Tetra Hyphessobrycon megalopterus — Seriously Fish (Hyphessobrycon megalopterus) high confidence
• Bleeding Heart Tetra Hyphessobrycon erythrostigma — Seriously Fish (Hyphessobrycon erythrostigma) high confidence
• Boesemani Rainbowfish Melanotaenia boesemani — Seriously Fish; Aquarium Co-Op Boesemani guide high confidence
• Bolivian Ram Mikrogeophagus altispinosus — Seriously Fish (seriouslyfish.com/species/mikrogeophagus-altispinosus) high confidence
• Brilliant Rasbora Rasbora einthovenii — Seriously Fish (seriouslyfish.com/species/rasbora-einthovenii) high confidence

Care-guide sources (8)

This guide synthesises the references below; where they disagree, the range and the disagreement are noted in the text above. The figures in the key-facts box are read from the TankStocking species database (v2026.06). Full welfare model on the methodology page.

• FishBase — Gymnocorymbus ternetzi — authority (Boulenger 1895), family (Acestrorhamphidae), max 7.5 cm SL, temp 20-26 °C, pH 6.0-8.0, dH 5-19, Paraguay & Guaporé basins to Argentina, pelagic, IUCN Least Concern (2021), diet/trophic 3.1, 'groups of 5 or more / 60 cm' note, highly commercial
• Seriously Fish — Gymnocorymbus ternetzi (Black Widow Tetra) — family (Characidae), common names, range, habitat 'dense overhanging vegetation', 6 cm, temp 20-26 °C, pH 6.0-7.0, GH 5-20, 20-gal-long tank, fin-nipper quote ('rectified by keeping it in a small shoal of at least 12 specimens'), beginner-friendly quote, diet, sexing, breeding, varieties (long-finned, leucistic, dyed-harmful, GloFish)
• AquariumStoreDepot — Black Skirt Tetra Care — size 1-2.5 in/up to 3, temp 70-82 °F, pH 6.0-7.5, GH 5-20, 15-20 gal, group 8+, 'they are fin nippers and that is not negotiable', avoid bettas/angelfish/fancy guppies/long-finned, good tankmates, diet, breeding, GloFish (GM, same care), dyed-fish warning, age colour-fade
• Wikipedia — GloFish — origin (Gong/NUS ~1999, jellyfish/coral GFP), Yorktown Technologies, Spectrum Brands (May 2017), species incl. black tetra, trademarked colours, FDA cleared Dec 2003, California banned 2003 / lifted 2015, EU import/sale/possession prohibited, breeding-prohibition licence quote
• Wikipedia — Black tetra — Boulenger 1895, synonym Tetragonopterus ternetzi, family Acestrorhamphidae, range (Pantanal/Paraguay/Paraná/Argentina), size 7.5 cm, lifespan 3-5/6+ yr, two black shoulder bars + grey body, egg-scattering, maturity ~2 yr, leucistic & GloFish variants
• Aquarium Source — Black Skirt Tetra 101 — lifespan 3-5 yr, ~3 in, temp 70-85 °F, pH 6.0-7.5, 15-20 gal, sexing, breeding difficulty 'Low', 'prone to nipping at flowy fins of betta fish or angelfish', tankmates
• fishstores.org — Black Skirt Tetra Care Guide — dyed/'fruit/color' tetra welfare quote ('bleaching strips the protective slime coat... cuts lifespan... down to 6 to 18 months'), dye process/legality, GloFish (GM, harmless, hereditary, can interbreed), long-finned strain needs 8+ group, core parameters, 8-10 redirects aggression inward
• Our Aquarium Life / GloFish.com store — long-finned strain more vulnerable to schoolmate nipping (keep 8+), size ~2.5-3 in, lifespan 3-5/6+, GloFish long-fin colour collections corroborating the GM long-fin product line (corroboration, not sole source for any number)

More on Black Skirt Tetra

Related guides on TankStocking — each scored by the same welfare engine as the planner.

This care guide is a sourced planning reference, not veterinary advice — individual fish, filtration and maintenance all matter. Cycle the tank, test your water, and observe your fish. How TankStocking works →