Black Widow Tetra (Gymnocorymbus ternetzi) 4cm

The Black Widow Tetra (Gymnocorymbus ternetzi), also widely known as the Black Skirt Tetra, is a hardy, active, and popular freshwater schooling fish native to the Paraguay River basin in South America. It is highly recommended for beginner aquarium hobbyists because it adapts easily to a wide range of water parameters and is very budget-friendly.

Species Overview

Scientific Name: Gymnocorymbus ternetzi

Adult Size: 2 to 3 inches (5 to 7.5 cm)

Lifespan: 3 to 5 years

Temperament: Generally peaceful but prone to fin-nipping

Diet: Omnivore

Tank Setup & Water Parameters

Black Widow Tetras are mid-to-top level dwellers that thrive in well-planted setups with plenty of open swimming space.

Minimum Tank Size: 20 gallons (approx. 75-114 liters) to accommodate a proper school.

Temperature Range: 68°F to 79°F (20°C to 26°C).

pH Range: 6.0 to 7.5.

Water Hardness: Up to 15 dGH.

Decor: They prefer dim lighting, floating plants, and dark substrates to mimic their natural river canopy environments.

Diet and Feeding

These fish are not picky eaters and will accept almost any food offered. To keep their colors vibrant and support health, offer a varied diet:

Base Diet: High-quality tropical flake foods or small sinking pellets.

Treats: Live or frozen brine shrimp, daphnia, bloodworms, or mosquito larvae.

Pro Tip: Ensure food particles are small enough to fit into their tiny mouths.

Behavior and Tank Mates

You must keep Black Widow Tetras in schools of at least 5 to 7 fish. Keeping them in a proper shoal keeps them feeling secure and significantly reduces aggressive bickering or fin-nipping behavior directed at other species.

Good Tank Mates: Peaceful, fast-moving fish of a similar size like other tetras (e.g., Neon Tetras), rasboras, Corydoras catfish, and opaline gouramis.

Fish to Avoid: Slow-moving fish with long, flowing fins like Bettas, Angelfish, or fancy guppies, as the Black Widow Tetra will nip at their fins. Avoid housing them with very tiny shrimp, which may be viewed as food.