Axelrod's Rainbowfish (Chilatherina axelrodi)

Chilatherina axelrodi, Axelrod's Rainbowfish, is a prized and relatively uncommon rainbowfish species native to the highland river systems of New Guinea (Papua New Guinea). Named in honour of Herbert R. Axelrod, the prolific American ichthyologist and aquarium publisher, this species represents the Chilatherina genus — a small group of rainbowfish closely related to Melanotaenia but with some distinct morphological differences.

Males are strikingly beautiful, displaying a deep blue to blue-green iridescent body that shimmers with different tones depending on the angle of light. The fins are adorned with orange to red colouration, particularly vivid in the dorsal and caudal fins, creating a dramatic contrast against the iridescent body. Females are less colourful, displaying a silver-green body with more muted fin colouring.

Like most rainbowfish, Axelrod's Rainbowfish is a schooling species that benefits greatly from being kept in groups of six or more. In a species school, males engage in constant competitive displays — fanning their fins and intensifying their colours — creating a dynamic and eye-catching spectacle. The species is entirely peaceful and makes an excellent community fish with other rainbowfish, larger tetras, barbs, and similarly active species.

This species prefers well-oxygenated, cool to moderate temperature water with good water quality. A spacious aquarium with open swimming space and some planted sections at the edges suits this active swimmer well.

Tank Setup: Minimum 120 litres for a school of six. Provide open mid-water swimming space with planted edges and background using hardy plants like Vallisneria or Cryptocoryne. Moderate to strong filtration with good water movement. A tight-fitting lid is recommended as rainbowfish can jump.

Water Parameters: Temperature 22–26°C; pH 7.0–8.0; GH 8–18 °dH; KH 5–10 °dH. Prefers slightly hard, neutral to slightly alkaline water — common in Belgian tap water and ideal for this species.

Feeding: Omnivore. Feed quality floating flake food, micro pellets, frozen bloodworm, brine shrimp, and Daphnia. Feed two to three times daily. Varied diet enhances colouration in males.

Tank Mates: Excellent with other rainbowfish, medium tetras, barbs, corydoras, loaches, and peaceful cichlids. Avoid slow-moving or very small fish that may be outcompeted at feeding time.

Behaviour: Peaceful, active, and energetic schooling fish. Males display constantly to each other when kept in a group — this is normal and non-harmful. Best kept in a ratio of two females per male to reduce male-male competition intensity.

Health: Hardy once acclimated. Sensitive to nitrate accumulation — keep below 20 ppm with regular water changes. Weekly 25% changes recommended.