Fish
Flag Tetra
Hemigrammus heterorhabdus
Origin: The flag tetra originates from the Amazon River basin in Brazil, primarily the Rio Negro and Tocantins rivers. It inhabits soft, acidic blackwater streams and forest pools rich in organic matter. Natural habitats feature dense vegetation, submerged leaf litter, and dark, tannin-stained water.
Also known as: Hemigrammus heterorhabdus, Flag Tetra
Fact sheet
- Size
- 4 cm
- Lifespan
- 4 years
- Minimum tank size
- 60 L
- Temperature
- 23–27 °C
- pH
- 6–7
- Hardness GH
- 2–8 °dH
- Temperament
- Peaceful
- Social behavior
- Schooling
- Swimming zone
- Middle
- Diet
- Omnivore
- Jumps out
- Yes
- Eats plants
- No
Overview
The flag tetra is a small characin prized for its striking tricolor horizontal stripe resembling a flag. Its peaceful temperament and vivid coloration make it a favorite in community aquaria. Best kept in groups of 8–10 or more, the fish displays bolder colors and more natural behavior in a school. A well-planted tank with soft, slightly acidic water replicates its natural biotope. Driftwood, almond leaves, and subdued lighting enhance the setup. Compatible with other peaceful small tetras, danios, and dwarf catfish, the flag tetra is relatively undemanding once stable water parameters are maintained. Consistent water quality is the key to vibrant coloration.
Appearance
The body is slender and semi-transparent with a silvery base color. The signature feature is a horizontal tricolor stripe: a bright red section near the tail, a black central band, and a golden-white sheen toward the head, evoking a national flag. Fins are transparent, slightly longer in males. Adults reach 4–4.5 cm. Sexual dimorphism is subtle; females are slightly larger and plumper.
Care
Provide a tank of at least 60 L with soft water (GH 2–8), pH 6.0–7.0, and temperature 23–27 °C. Good filtration and 25–30% weekly water changes are essential. Decorate with driftwood, Indian almond leaves, and live plants. Subdued lighting or floating plants reduce stress. Maintain stable parameters, as fluctuations cause color fading and disease susceptibility.
Feeding
An omnivore with a small mouth. Accepts quality flake food and micro-pellets; relishes live or frozen cyclops, baby brine shrimp, and daphnia. Feed twice daily in small portions. A varied diet preserves vibrant coloration and overall health.
Compatibility
Peaceful and schooling. Excellent tankmates include other small tetras, danios, rasboras, dwarf gouramis, and small Corydoras. Avoid housing with large or aggressive species. Keep in groups of at least 8 to minimize stress and encourage natural shoaling behavior.
Breeding
Spawning is triggered by very soft water (GH under 4) and pH 6.0–6.5. Fish scatter eggs among fine-leaved plants. Remove adults after spawning to prevent egg predation. Eggs hatch in 24–36 hours; fry become free-swimming after 3–4 days and accept infusoria or micro-worm as first foods.
Fun facts
The tricolor stripe acts as a shoal cohesion signal. The common name 'flag tetra' directly references this pattern. The species was described by Ulrey in 1894. Under stress or poor conditions, the stripe noticeably fades.