Costae Tetra or Blackline Tetra (Moenkhausia costae)

Add a touch of sophisticated movement to your aquarium with the Costae Tetra (Moenkhausia costae), also frequently known as the Blackline Tetra or Fortune Tetra. Distinguished by its sleek silver body and a bold, deep-black horizontal stripe that extends through the lower lobe of the tail fin, this species is a standout choice for hobbyists seeking an active, schooling fish with a unique silhouette.

Place of Origin

The Costae Tetra is native to South America, specifically the São Francisco and Itapicuru River basins in Brazil. They are typically found in large schools within clear to slightly turbid river channels and floodplains, where they navigate through driftwood and aquatic vegetation.

Care Level & Environment

• Care Level: Easy to Moderate. They are hardy fish but thrive best in well-maintained environments with consistent water parameters.

• Water Conditions: They are adaptable but prefer slightly alkaline to neutral water.

  • Temperature: 72°F - 82°F (22°C - 28°C)

  • pH: 6.5 - 7.5

  • Hardness: 5 - 15 dGH

• Aquarium Setup: To best display the Blackline Tetra, provide a long aquarium with plenty of open swimming space. A landscape featuring a dark substrate, river stones, and hardy plants like Vallisneria or Echinodorus(Amazon Swords) mimics their natural riverine habitat. Using driftwood branches can provide a natural aesthetic while offering minor retreats.

Tank Size

Because the Costae Tetra is a powerful and energetic swimmer, they require more lateral space than smaller tetra species.

• Minimum Tank Size: 30 to 40 gallons is recommended for a small school.

• Schooling Requirements: To see their natural behavior and reduce stress, they should be kept in groups of at least 6 to 10 individuals. In larger groups, their synchronized schooling behavior is truly impressive.

Diet & Feeding

Moenkhausia costae is an unfussy omnivore with a high metabolism.

• Staple Diet: High-quality dry flakes or small floating pellets.

• Live/Frozen Foods: They will show improved color and vigor if supplemented with brine shrimp, bloodworms, and daphnia.

• Feeding Tip: They are top-to-middle dwellers and are very fast during feeding time, so ensure that slower bottom-dwelling tank mates are also receiving food.

Tank Mates

The Costae Tetra is a peaceful but very active fish. Their speed can sometimes startle very slow-moving or shy species.

• Ideal Tank Mates: Similarly sized tetras, Rainbowfish, larger Rasboras, Corydoras catfish, and peaceful South American Cichlids like Geophagus or Blue Rams.

• Avoid: Very small shrimp (which may be seen as food) or extremely long-finned, slow fish that might be bothered by the Costae’s fast-paced swimming.

Breeding Costae Tetras

Breeding Moenkhausia costae in the home aquarium is considered a challenge but is possible for the dedicated breeder.

1. Preparation: Condition a group with high-quality live foods. Use a separate breeding tank with soft, slightly acidic water and a mesh bottom or "spawning grass" to protect the eggs.

2. Spawning: They are egg-scatterers. Morning sunlight often triggers spawning.

3. Fry Care: Adults must be removed immediately after eggs are laid. The fry will hatch in 24–36 hours and will require infusoria or specialized liquid fry food until they are large enough to accept baby brine shrimp.

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