The Costae Tetra (Moenkhausia costae), also frequently called the Blackline Tetra or Black Line Tail Tetra, is a sleek, energetic schooling fish native to the river basins of eastern Brazil. Known for its shimmering silver body and a distinct black horizontal line that extends into its tail fin, it is a popular choice for planted community aquariums due to its active nature and tight schooling behavior.
Key Characteristics & Behavior
Appearance: Features a metallic silver-to-green body with a subtle golden or blue sheen. Its defining trait is the sharp black line running from the midsection or anal fin through the tail.
Size: Typically grows to a maximum length of 5–7 cm (2–2.75 inches).
Social Dynamics: They are highly social and must be kept in groups of at least 6 to 10 individuals. In smaller groups, they can become nervous or exhibit nipping behavior toward tank mates.
Activity Level: Known for being fast-moving and energetic, they occupy the middle and upper levels of the tank. They are also prone to jumping, so a tightly covered lid is essential.
Aquarium Care Requirements
To keep Costae Tetras healthy, aim for the following conditions:
Tank Size: A minimum of 60–100 litres (approx. 15–25 gallons). Long tanks (at least 30 inches) are preferred over tall ones to allow for their active swimming.
Water Parameters:
Temperature: 22°C to 28°C (72°F to 82°F).
pH: 6.0 to 7.5.
Hardness: 2 to 15 dGH.
Environment: Thrives in planted aquascapes with driftwood and some floating plants to provide shade, as they prefer moderate to dim lighting.
Diet: Omnivorous and undemanding. They readily accept high-quality flakes, pellets, and frozen or live foods like brine shrimp, daphnia, and bloodworms.
Community Compatibility
They are generally peaceful and pair well with other non-aggressive species like smaller tetras, rasboras, Corydoras catfish, and peaceful dwarf cichlids. Avoid housing them with slow-moving or long-finned fish, as they may occasionally nip if their own school is too small.
SKU: RBM
