Not furry, but we like them anyway.
Black Skirt Tetra
Gymnocorymbus ternetzi
Also called Black tetra, Black widow tetra, Butterfly tetra, Petticoat tetra, High-fin black skirt tetra
From South America: the Paraguay and Guaporé river basins in Brazil (largely the Pantanal), Bolivia, Paraguay and northern Argentina123
A friendly guide, not veterinary advice. For anything about your pet's health, ask your vet.
At a glance the quick version
Looks how to spot one
Small scaled characin (tetra) with an adipose fin
A deep-bodied, rather flat tetra with a tall dorsal fin and a broad, flowing anal fin that looks like a little skirt. The body shades from pale silver-grey at the nose to near black towards the tail, with two dark vertical bars just behind the gill cover. Young fish are the darkest and the colour softens a little as they mature. Males are slimmer, with more pointed dorsal and anal fins.32
Personality what they are like
An easygoing shoaling fish that gets along well with livebearers, danios, rasboras and other tetras. It is livelier and more settled in a big group, which also keeps any playful fin nipping in check, so long-finned or very slow tankmates are best avoided.2
Daily activity how busy a day looks
Active swimmer that uses the middle and upper parts of the tank; give it open swimming room alongside planted areas.12
Grooming and care the hands-on bits
No grooming needed. Regular partial water changes and a varied diet keep it in top shape. All fish in the trade are captive bred and adapt readily to a wide range of tap water.2
Home where they are happiest
Tank of at least about 60-75 cm long (around 68 litres) for a group. Temperature 20-26 °C, pH 6.0-8.0 (Seriously Fish suggests 6.0-7.0), hardness about 5-20 dGH.12
Food basics what goes in the bowl
Omnivore. In the wild it eats worms, small crustaceans and insects; in the aquarium it takes flakes and granules plus small live or frozen foods such as Daphnia and bloodworm.12
Company who they like around
Shoaling fish: FishBase advises groups of 5 or more, while Seriously Fish recommends a shoal of at least 12 to keep behaviour calm.12
The story where it all began
Described by George Albert Boulenger in 1895 as Tetragonopterus ternetzi, it has since become one of the most widely available tetras in the hobby. Fish sold today are bred in captivity, and the species was also one of the fish used to create the fluorescent GloFish lines.32
Fun facts for the dinner table
- 1
The flowing black anal fin is what earned it the nickname 'black skirt' or 'petticoat' tetra.3
- 2
It was one of the species used to make the genetically modified GloFish, which come in a rainbow of fluorescent colours.3
- 3
Juveniles show the deepest black colouring, which gently fades to grey as the fish grow up.2
- 4
A leucistic form with a pale, almost white body is sold as the 'white skirt tetra'.2
Recognised by the official bits
- IUCN Red List
- Least Concern (assessed 4 March 2021)1
- FishBase
- Rated highly commercial in the aquarium trade1
The care rhythm Furry Diary remembers it for you
A typical home-care rhythm for a Black Skirt Tetra. It is our own starting plan, not a vet's advice, and you can change every line in the app.
- FeedingSmall amounts once or twice a dayevery day
- Temperature checkevery day
- Water changeAbout 25% of the waterevery week
- Water testevery week
- Glass cleanevery week
- Filter rinseRinse in old tank water, never tap waterevery month
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Where this comes from
Every breed page shows where each fact comes from. If we got something wrong, sorry, we are pet people, not a science magazine. Tell us at support@furrydiary.app and we will fix it.
- FishBase species summary: Gymnocorymbus ternetzi (Black tetra) fishbase.seused for origin, maximum length, water parameters, natural diet, IUCN status, trade use
- Seriously Fish species profile: Gymnocorymbus ternetzi seriouslyfish.comused for aquarium size, water parameters, diet, behaviour, group size, sexing, naming
- Wikipedia: Black Skirt Tetra en.wikipedia.orgused for other names, appearance, lifespan, history, fun facts
Checked 2026-09-30. Text is written in our own words from these sources.