Common name
Black skirt tetra
Scientific name
Gymnocorymbus ternetzi
Category
Freshwater fish
Group
Tetras and characins
Environment
Mature freshwater aquarium with open middle-water space and planted or wooded margins
Origin
Paraguay and Guaporé river basins in southern South America
Care level
Beginner to intermediate
Adult size
About 6 cm standard length; around 7.5 cm total length
Expected lifespan
Plan for approximately 5–8 years and potentially longer under stable schooling care.
Minimum housing
At least 90 L with an 80 cm or longer footprint for ten or more fish
Temperature
22–27 °C
pH
Unknown; stable source-matched chemistry is more important than chasing a generic value
Hardness / minerals
Unknown; avoid abrupt mineral change
Salinity
Freshwater, 0 ppt; routine salt addition is not recommended
Lighting
Moderate, with shaded refuge
Placement / zone
Middle water
Filtration
Use mature biological filtration sized for the complete adult black skirt tetra group, with guarded intakes and accessible mechanical capture. Keep flow moderate with open swimming lanes and dependable surface exchange where the fish lives, and maintain undetectable ammonia and nitrite.
Aeration
Maintain reliable surface agitation and oxygen exchange at all times. Increase aeration during warm weather, medication, transport recovery, heavy feeding or any sign of rapid breathing.
Maintenance
Perform regular matched-water changes guided by nitrate and waste, remove uneaten food and trapped detritus, clean mechanical media without disrupting the biofilter, and record feeding, body condition, respiration and aggression.

Identity and search names

Single-species profile for Gymnocorymbus ternetzi, including ordinary black, white and long-fin domestic forms. Commercial branded colour lines are not separate species.

Search names: Black widow tetra, Black tetra, White skirt tetra

Environment and housing

Provide a long open swimming lane, planted or wooded margins, mature filtration and secure cover.

Social structure: Keep at least ten; larger groups reduce directed fin-nipping

Feeding and nutrition

Feeding ecology: Omnivore; fine prepared foods plus small invertebrate foods

Feeding routine: Offer one or two small measured meals daily

Breeding, reproduction or spread

Iteroparous batch-spawning egg scatterer; adults provide no care and may eat eggs

Detailed care and app-ready planning

Identity scope
Single-species profile for Gymnocorymbus ternetzi, including ordinary black, white and long-fin domestic forms. Commercial branded colour lines are not separate species.
Adult size and space
Adults reach about 6 cm standard length and roughly 7.5 cm total length. Use at least 90 L with 80 cm or more of frontage for ten or more fish.
Social structure
Maintain at least ten. Larger groups spread chasing and reduce the chance that one fish receives repeated fin-nipping.
Swimming zone or placement
Middle water, using open lanes between planted or wooded margins.
Feeding ecology
Generalist omnivore taking small aquatic invertebrates and other appropriately sized foods.
Feeding plan
Offer quality flakes or small pellets and small frozen invertebrates once or twice daily. Feed over a broad area.
Water stability
Maintain 22–27 °C with zero ammonia and nitrite and no rapid temperature or chemistry changes. Reliable universal pH and hardness limits were not independently established.
Habitat structure
Use open horizontal swimming space, planted or wooded borders, subdued refuge and mature filtration.
Compatibility plan
Choose active peaceful tankmates of similar size. Avoid long fins, very slow feeders and fish small enough to be bullied.
Breeding or reproduction plan
Use a separate spawning aquarium with fine plants or mesh, remove adults after spawning and provide microscopic first foods for fry.
Quarantine
Quarantine in a separate cycled aquarium with dedicated nets, containers and siphons. Match temperature and mineral chemistry gradually, confirm normal feeding, respiration, skin, fins and waste, and never pour transport water into the established aquarium.
Welfare checks
Check school cohesion, fin edges, body depth, respiration, colour and equal feeding access.
Biosecurity and release
Never release fish, fry, eggs, aquarium water, sediment, plants or foods into drains, dams or natural waterways. Check the exact accepted scientific name in current BICON and applicable South Australian rules before import, sale or movement; import eligibility does not authorise release or wild collection.
Main risk
An undersized group concentrates chasing and fin damage; domestic colour does not change that requirement.
Adult projected load
Project biological load from the full adult black skirt tetra group, adult body mass, feeding pattern, activity and social requirement rather than juvenile sale size. A school of deep-bodied tetras creates a moderate combined biomass and feeding load; long fins and domestic colours do not remove normal social needs.
Filtration
Use mature biological filtration sized for the complete adult black skirt tetra group, with guarded intakes and accessible mechanical capture. Keep flow moderate with open swimming lanes and dependable surface exchange where the fish lives, and maintain undetectable ammonia and nitrite.
Aeration
Maintain reliable surface agitation and oxygen exchange at all times. Increase aeration during warm weather, medication, transport recovery, heavy feeding or any sign of rapid breathing.
Maintenance
Perform regular matched-water changes guided by nitrate and waste, remove uneaten food and trapped detritus, clean mechanical media without disrupting the biofilter, and record feeding, body condition, respiration and aggression.
Overridable warnings
Non-overridable: do not accept persistent ammonia or nitrite, oxygen distress, starvation, chronic aggression or inadequate adult space. Different equipment, stocking or maintenance methods may be used only when measured water quality and adult welfare remain equivalent or better. A group of ten or more and enough footprint to distribute chasing are mandatory; dyed, tattooed or severely deformed fish should not be purchased.

Compatibility, welfare and risk

Compatibility: Use active similarly sized community fish; avoid very slow, timid or long-finned tankmates.

Welfare: Check schooling, fin condition, body depth, feeding access and whether one fish is repeatedly targeted.

Main warning: Domestic colour and fin forms do not reduce adult size or social needs. Do not use a branded trade name as though it were a separate species.

Biosecurity and release

Never release fish, fry, eggs, aquarium water, sediment, plants or foods into drains, dams or natural waterways. Check the exact accepted scientific name in current BICON and applicable South Australian rules before import, sale or movement; import eligibility does not authorise release or wild collection.

Sources