Black Skirt Tetra (Gymnocorymbus ternetzi)

Gymnocorymbus ternetzi, the Black Skirt Tetra (also called Black Widow Tetra or Petticoat Tetra), is one of the hardiest and most adaptable tetras available in the aquarium hobby. Native to the Paraguay and Guaporé River basins in Bolivia, Brazil, and Argentina — including the extraordinary Pantanal wetlands — it is a resilient species that tolerates a very wide range of water conditions.

The juvenile and young adult colouration is distinctive: a silver body with two dark vertical bars behind the head and large, flowing black dorsal and anal fins that taper toward the tail, creating the 'skirt' silhouette. As fish age, the black colouration fades somewhat to a more grey-silver, though young specimens are boldly marked.

Black Skirt Tetras are available in several additional colour morphs including the 'GloFish' fluorescent varieties and a long-finned variant with dramatically extended fins. These captive-bred forms are popular in the wider aquarium market.

This species is notably more fin-nipping prone than many tetras, particularly when kept in small numbers or with very slow, long-finned fish. Keeping groups of eight or more significantly reduces fin-nipping as intra-group interaction dominates. A robust community tank with other active, medium-sized fish and no Angelfish or Bettas is the ideal setting.

Tank Setup: A minimum 80-litre aquarium for a school of eight. Moderate to strong filtration. Provide open mid-water swimming space with plants along the sides and back. Not particularly demanding about decor or substrate — very adaptable.

Water Parameters: Temperature 20–26°C; pH 6.0–8.0; GH 5–20 °dH; KH 3–15 °dH. Exceptionally tolerant of a wide range of water conditions — suitable for virtually any tap water in Belgium. One of the most adaptable tetras available.

Feeding: Omnivore. Accepts virtually any aquarium food: flake, pellets, frozen and live foods. Feed two to three times daily. Active and enthusiastic feeders that compete well at mealtimes.

Tank Mates: Best with robust, active species of similar size. Compatible with barbs, danios, medium tetras, corydoras, loaches, and rainbowfish. Avoid very slow fish with flowing fins (Bettas, Angelfish, Guppies) due to fin-nipping tendency. Keep in groups of 8+.

Behaviour: Active, fast-moving schooling fish. Fin-nipping tendency is significantly reduced in groups of 8 or more. Males may chase each other briefly but this is harmless within the school.

Health: One of the hardiest tetras in the hobby. Rarely ill when kept in appropriate conditions. Tolerates a wide range of temperature and chemistry. Weekly 25% water changes recommended for long-term health.