Black Skirt Tetra
Gymnocorymbus ternetzi
Min Tank Size
75L
Adult Size
6 cm
Lifespan
5 years
School Size
6+
About
Native to the Paraguay and Guapore river basins in South America, black skirt tetras have been a staple of the hobby for decades. And honestly, it's easy to see why.
Young fish come in with that striking deep black coloration across the rear half of the body and flowing anal fins, though fair warning: that bold black fades considerably as they age, often shifting to a dull gray by adulthood. It's one of the more common surprises for new keepers who bought them for their looks. They're sold under a few names, including petticoat tetra, and you'll also find albino (White Skirt) and fluorescent GloFish variants at most chain stores. All are the same species underneath.
Water parameters are refreshingly flexible. They handle a pH anywhere from 6.0 to 7.5 and tolerate temperatures on the cooler side compared to many tropicals, down to around 20°C. That broader range makes them genuinely beginner-friendly. They're not fussy eaters either. Flake, micro pellets, frozen bloodworms, daphnia, and brine shrimp all get eaten without hesitation.
Where things get more nuanced is their temperament. Black skirts are confirmed fin nippers, not occasional offenders. Long-finned tankmates like bettas, angelfish, and guppies are going to have a bad time sharing a tank with them. In a well-matched community they're fine, active schoolers that add movement to the mid-water column. Keep them in groups of at least six or the nipping behavior amplifies and you'll start seeing stressed tankmates.
Browse real builds featuring this species to see how experienced keepers work around their quirks while getting the most out of their energy and activity.
Water Parameters
Temperature
°CpH
GH
dGHKH
dKHSwimming Level
Flow Preference
Keeping multiple Black Skirt Tetra together
Black Skirt Tetra are shoaling fish and need company of their own kind. Keep a group of at least 6. Smaller groups leave them stressed, washed-out in color, and prone to hiding.
Compatibility
Good tankmates are similarly sized, short-finned, and fast enough to hold their own. Zebra danios, tiger barbs (which can actually nip back), Buenos Aires tetras, corydoras, and larger rasboras all tend to coexist fine. Mid-sized plecos and robust bottom dwellers work well too since black skirts stay in the mid column and don't bother them. Hard no's include bettas, fancy guppies, angelfish, and any fish with flowing finnage. Dwarf shrimp are sometimes picked at, especially smaller juveniles. In tanks over 120 liters they become much easier to manage in mixed communities.
Commonly kept with
Species this one is most often paired withCommonly tried but avoid
Often paired, but shouldn't beCare Notes
The most common beginner mistake is buying two or three and wondering why the tank dynamic falls apart. Six is the real minimum, and eight works better. The other thing people get wrong is pairing them with angelfish or bettas because they look nice together, only to find shredded fins within a week. Their color fading with age also catches people off guard. Good filtration with moderate flow, regular water changes, and a varied diet keep them healthy with minimal effort. They're genuinely one of the easier tetras to keep alive long-term.
Behavior & Aggression
Black skirt tetras are reliable fin nippers, not occasional ones. The behavior is most intense with long-finned or slow-moving fish like bettas, angelfish, guppies, and fancy livebearers. Nipping tends to increase when schools are small (under six fish), when the tank is overcrowded, or when food is scarce. Keeping a larger school redistributes their attention internally and reduces targeted harassment of other species. Well-fed, properly schooled groups in a spacious tank are considerably calmer, but the underlying tendency never disappears completely.
Things to Know
- Habitual fin nipper, avoid tankmates with long flowing fins
- Keep in groups of 6+ or nipping behavior worsens significantly
- GloFish and White Skirt variants are the same species, same care
- Can be nippy, especially towards slow, long-finned fish.
- Must be kept in a school of 6+ to reduce stress and aggression.
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