Allen's Rainbowfish

Allen's rainbowfish grows to about 10 cm as an adult. The colour displays a wide spectrum of shades: predominantly blue, light blue, red and orange. All colour variants share a noticeable blue stripe running along the lateral line. The dorsal, anal and caudal fins have red edges.

This species is endemic to New Guinea and inhabits river systems in the West Papua region. The fish live in both small forest streams and large rivers, preferring areas with moderate current and abundant sunlight. In their natural habitat, the substrate typically consists of gravel or sand with fallen leaves and driftwood. Water parameters in nature vary widely: temperature ranges from 24–31 °C, and pH from 6.0 to 8.4.

These fish are quite mobile and peaceful, with a natural tendency to school. Buy them in groups of 6–8 individuals. They get along well with most other non-aggressive species. However, slower tank mates may struggle to compete for food, so choose companions carefully.

For a group of 6–8 individuals, the aquarium should be at least 150 litres. Arrange the tank to provide both open swimming space and sheltered areas made from dense plants and driftwood. The fish adapts easily to different water parameters, which simplifies care, provided pH and dH remain stable. It prefers bright lighting and warm water; avoid prolonged temperatures below 24 °C. Tank maintenance is standard: weekly partial water changes with removal of organic waste. In nature its diet consists of small insects falling into the water, their larvae, and zooplankton. In captivity the fish readily accept all popular foods: dry, frozen and live.

In nature, this fish feeds on small insects and their larvae, as well as zooplankton that falls into the water. In the aquarium it adapts easily to various foods, including frozen, live and dry.

For breeding, use a separate spawning tank with fine-leaved plants or synthetic substrate to anchor eggs. Spawning is paired or in groups, triggered by raising water temperature and feeding live foods generously. The female deposits eggs in portions over several days. The incubation period at 22–24 °C lasts about 15 days. Fry require small starter foods such as infusoria or specialized dry fry food, and grow rapidly with regular water changes.

Allen's rainbowfish has a robust immune system when kept in clean, well-aerated water. Like other rainbowfishes, this species is sensitive to accumulation of organic compounds and nitrogen cycle breakdown products; neglecting tank hygiene can trigger bacterial infections or fin damage. The most likely problems under poor conditions include fin rot, shown by destruction of fin edges; white spot disease, which occurs after sudden temperature swings or introduction of infected fish; and skin parasites caused by poor water quality. Prevention involves regular water changes, maintaining stable parameters, and quarantining new fish. Avoid overcrowding, as stress from territorial competition weakens resistance to infectious disease.

When selecting fish, pay attention to activity and behaviour: healthy rainbowfish should be mobile, show interest in their surroundings and school together. Examine the body carefully for damage, spots, sores or signs of parasites. Avoid fish showing signs of emaciation, a sunken belly, or abnormally clamped fins. Young fish may have less vivid colour, but the overall body shape should match the species standard without spinal deformations.