Black skirt tetra

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Feeding

An undemanding omnivore. Flake, pellets, frozen bloodworm, frozen brine shrimp, frozen daphnia, live foods, and small bits of blanched vegetable are all accepted. The fish is fast at the surface and not at all shy at feeding time, so in a community it will get its share and usually a little extra. Twice a day in modest amounts works well. Variety improves colour and fin condition; a diet of dry food alone is enough to keep the fish alive but not at its best.

Compatibility

• Hardy and active, with a touch of pushiness. Not a dedicated fin-nipper like a tiger barb, but it will chase and nip occasionally, mostly when kept in small groups or alongside slow long-finned fish
• Best in groups of six or more (suggests twelve or more for nipping to be confined to the school), paired with mid-sized, robust tankmates: other tetras, barbs, rainbowfish, peaceful cichlids, and corydoras-class bottom dwellers
• Avoid the obvious bad pairings with long-finned fish: bettas, angelfish, fancy guppies. The flowing fins are the trigger
• Confusingly marketed under multiple names (black skirt, black widow, petticoat, blackamoor, white skirt for the albino), and also as artificially coloured 'fruit tetras' and as transgenic GloFish. The GloFish variants need the same care as the parent species; the dyed fish are best avoided
• Tolerant of a wide range of water conditions, which is part of why this is a long-standing beginner's tetra

Origin and habitat

A characin from the rio Paraguai basin in south-central Brazil (mainly the Pantanal), Paraguay, and northeastern Argentina, with additional populations in the upper Parana and rio Paraiba do Sul that were almost certainly introduced through the ornamental trade. Older records from the Guapore river have since been reassigned to a separate species, G. flaviolimai, described by Benine and colleagues in 2015 and confined to the Madeira basin. Boulenger described the species in 1895, originally placing it in Tetragonopterus, and the current placement is in the genus Gymnocorymbus within the American-characin family Acestrorhamphidae. Wild habitat is small, slow tributaries shaded by overhanging forest. The body is roughly tetragonal in outline and compressed sideways, with a greyish ground colour that grades from a near-black tail to a paler head; two prominent dark vertical bars sit behind the gills, and the long, deep anal fin gives the species its 'skirt' silhouette. Long-finned and albino strains exist; the albino is the basis of the so-called 'white skirt' tetra. The dark colour fades as fish age and old specimens look noticeably greyer than juveniles. Adults usually reach about 6 cm, with reports up to roughly 7.5 cm. IUCN Least Concern. Two consumer-trade issues sit alongside the species: dyed 'fruit tetras' (sometimes labelled Berry Tetra or Painted Tetra) are white-skirt fish dipped in coloured dye, a process that injures the fish and shortens its lifespan and is widely condemned by welfare-aware retailers; and the fluorescent GloFish tetras (sold in trademarked colours Starfire Red, Moonrise Pink, Sunburst Orange, Electric Green, Cosmic Blue, and Galactic Purple) are genetically modified G. ternetzi with fluorescent protein genes inserted, so the colour is permanent rather than applied.

Breeding

Spawns as an open-water egg scatterer and is one of the easier tetras to breed at home. Condition a chosen pair on frozen food for a week or so. The breeding tank wants fine-leaved plants or a spawning mop, soft water (GH below about 8), and a temperature around 26 to 27 C. Spawning happens at dawn after a courtship of roughly three hours, with the female releasing batches of slightly adhesive eggs that fall among the plants while the male fertilizes them. The parents will eat their eggs once spawning ends, so they need to come out promptly. Hatching takes around one to one and a half days at typical aquarium temperatures. The fry are fairly large for a characin and start on baby brine shrimp not long after they become free-swimming. The species is bred commercially in large numbers, which is why it remains inexpensive in the trade. Sexual maturity is reached at about two years.

Common problems

The colour fading that happens with age is the most common 'is something wrong with my fish' question. Juveniles are strikingly dark and adults of two or three years look noticeably greyer; this is normal development, not a disease. A darker substrate and dimmer lighting hold the contrast a little longer but do not stop the process. Ich is fairly common in newly bought fish, particularly from high-turnover stores; standard treatments are well tolerated. The other regular issue is fin-nipping behaviour. The species has a reputation as an occasional nipper despite being mostly peaceful otherwise, and the standard mitigation is to keep them in a larger group (suggests at least twelve, others put the minimum lower) so that the squabbling stays inside the school rather than spilling onto long-finned tankmates.

Bioload

Further reading

• Why your angelfish ate your neons