Black widow tetra
Gymnocorymbus ternetzi
A hardy, deep-bodied tetra with black 'skirt' fins; easy for beginners, but a small group nips the fins of its tank mates.
Key facts
- Body length
- 2.4 in without fins
- Minimum tank
- 22 gallons
- Group
- 12+
- Temperament
- Peaceful
- Care level
- 1 / 5
- Lifespan
- Not well documented
- Diet
- Flakes, micro pellets, frozen bloodworm and daphnia
- Origin
- Paraguay and Guaporé basins, South America
- Hardier than59%
- Bigger than36%
- Calmer than68%
Water: their range vs yours
Black widow tetra tank mates
- Neon tetraGets along in shared water.Good mates
- Harlequin rasboraGets along in shared water.Good mates
- Panda corydorasGets along in shared water.Good mates
- OtocinclusGets along in shared water.Good mates
- Cherry shrimpGets along in shared water.Good mates
- Tiger barbGets along in shared water.Good mates
- Amano shrimpGets along in shared water.Good mates
- Black neon tetraGets along in shared water.Good mates
- Blood parrot cichlidGets along in shared water.Good mates
- Bristlenose plecoGets along in shared water.Good mates
- Bronze coryGets along in shared water.Good mates
- Cardinal tetraGets along in shared water.Good mates
- Fancy guppyMay nip guppy tails in small groups.Risky
- AngelfishAngelfish eats small fish: Black widow tetra.Risky
- DemasoniDemasoni (aggressive) will bully the peaceful Black widow tetra.Risky
- Firemouth cichlidFiremouth cichlid can eat young or small Black widow tetra; adults are big enough to be safe.Risky
- Golden mbunaGolden mbuna (aggressive) will bully the peaceful Black widow tetra.Risky
- GoldfishGoldfish can eat young or small Black widow tetra; adults are big enough to be safe.Risky
- BettaBlack widows nip betta fins.Avoid
- Blue dolphin cichlidBlue dolphin cichlid can eat Black widow tetra: prey body depth 2.4 cm ≤ mouth 6.3 cm.Avoid
- Convict cichlidConvict cichlid can eat Black widow tetra: prey body depth 2.4 cm ≤ mouth 3.8 cm.Avoid
- Iridescent sharkIridescent shark can eat Black widow tetra: prey body depth 2.4 cm ≤ mouth 32.5 cm.Avoid
- Jewel cichlidJewel cichlid can eat Black widow tetra: prey body depth 2.4 cm ≤ mouth 3.8 cm.Avoid
- OscarOscar can eat Black widow tetra: prey body depth 2.4 cm ≤ mouth 12.3 cm.Avoid
How we check
The numbers the tank model uses for black widow tetras: water as ideal and tolerated ranges, bioload from adult mass, space, flow and how they act on other species.
- Standard length
- 6 cm (SL)
- Adult mass
- 7.74 g
- Bioload at 25 °C
- 3.93 BU
- Min. water
- 68 L net
- Min. footprint
- 75 × 30 cm per group
- Group
- 12+ (best 12)
- Swims in
- middle
- Flow
- low
- Body / fins
- deep bodied, normal fins
- Diet type
- omnivore
- Fin nipper
- occasional
- Sensitive to
- —
Sources: Seriously Fish: Gymnocorymbus ternetzi · FishBase: Gymnocorymbus ternetzi
Care notes
Black widow tetras come from slow, overgrown streams of the Paraguay and Guaporé basins. They are tough and adaptable, and long-finned, albino and GloFish forms are sold alongside the wild type.
Keep a group of twelve in a 20 gallon tank or larger with a 30-inch footprint; in a big group the nipping mostly stops. Avoid long-finned or slow tank mates, and skip artificially dyed fish, which live noticeably shorter lives.
Questions
What size tank does a black widow tetra need?
At least 22 gallons (68 litres of water after decor). Adults reach about 2.4 inches without fins.
How many black widow tetras should be kept together?
Keep at least 12, ideally 12 or more: fewer feel exposed and hide or turn nippy.
What water do black widow tetras need?
68–79 °F, pH 6–7 and 5–20 dGH. Black widow tetras come from Paraguay and Guaporé basins, South America.
How long do black widow tetras live?
Not well documented with good care.
What fish can live with black widow tetras?
Good tank mates include Neon tetra, Harlequin rasbora, Panda corydoras, Otocinclus and Cherry shrimp. Each is checked both ways for size, fin nipping, temperament, territory and shared water.