An Introduction to Black Skirt Tetras
Gymnocorymbus ternetzi, commonly called the black skirt tetra or black widow tetra, is native to the Paraguay and Guaporé river basins of Brazil, Bolivia, and Paraguay. It is a larger tetra than most community species, reaching 2 to 3 inches at full size. Its signature feature is a pair of deep black vertical bars on the anterior body and a large, flowing black anal fin that gives the species its "skirt" nickname.
As black skirt tetras mature, their bold black coloration often fades to gray — this is normal and not a sign of illness. Long-finned varieties exist, and genetically modified GloFish versions (fluorescent green, pink, orange, and blue) are widely available, though long-finned and GloFish varieties are slightly less hardy than the wild-type.
Tank Size
Black skirts need more space than most small tetras. Minimum tank size is 20 gallons for a school of 6. A 29-gallon long tank handles 8 to 10, and 40-breeder or larger tanks accommodate impressive schools of 12 or more plus tank mates.
Horizontal swimming space is critical. Black skirts are active mid-water swimmers and quickly become frustrated in short tanks. Never keep them in tanks under 24 inches long.
Water Parameters
Black skirts are one of the hardiest tetras available. They tolerate a wide range of water conditions, making them ideal for beginners and hard-water keepers. Target temperature is 72 to 80°F (22 to 27°C). Target pH is 6.0 to 7.5. Target hardness is 5 to 20 dGH — they handle moderately hard water well.
This flexibility is why black skirts remain popular despite being overshadowed by flashier species. They survive the common beginner mistakes that kill more sensitive tetras.
Behavior and Potential Fin Nipping
Black skirts are usually peaceful, but under-schooled individuals can become fin nippers, especially targeting long-finned tank mates like angelfish, bettas, and guppies. The solution is always the same: keep a proper school of 6 or more (ideally 8 to 10). In proper schools, the fish focus on their own group dynamics and ignore tank mates.
Avoid keeping black skirts with any long-finned or slow-moving species. Good companions include other similar-sized tetras, Corydoras catfish, peaceful barbs, rainbowfish, and small peaceful cichlids.
- ✦Keep in schools of 6-10 minimum to prevent fin nipping
- ✦Avoid long-finned tank mates like angelfish, bettas, and fancy guppies
- ✦Pairs with active mid-water species well
- ✦Long-finned and GloFish varieties need identical care but are slightly more delicate
Feeding
Black skirts are enthusiastic omnivores with larger mouths than most tetras. They accept standard flake food easily, along with pellets, frozen foods, and live foods. Feed a high-quality tropical flake as the daily staple with 2-3 weekly treats of frozen bloodworms, brine shrimp, or daphnia.
Adult black skirts can be aggressive at feeding time and may outcompete smaller tank mates. Feed at multiple spots in the tank, or use sinking pellets to ensure bottom-dwellers get their share.
Breeding
Black skirts are egg scatterers and moderately easy to breed in captivity. Set up a small 10 to 15-gallon breeding tank with soft, slightly acidic water, a spawning mop or dense plant cover, and dim lighting. Condition a pair with live foods for 1 to 2 weeks.
Spawning produces several hundred eggs scattered over plants. Adults will eat the eggs — remove them immediately after spawning. Fry hatch in 24 to 36 hours and become free-swimming at 4 to 5 days. Feed infusoria, then baby brine shrimp as they grow.