Lake Kutubu Rainbowfish

The Lake Kutubu Rainbowfish (Melanotaenia lacustris), commonly known as the turquoise rainbowfish or blue rainbowfish, is a striking freshwater fish endemic solely to Lake Kutubu and its outlet in the Kikori River system of Papua New Guinea. Renowned for its brilliant, shifting hues of cobalt, aqua green, and turquoise, it is a highly prized yet sensitive choice for dedicated aquarium hobbyists.

Quick Species Overview

Parameter	Detail
Scientific Name	Melanotaenia lacustris
Adult Size	4 to 5 inches (10 to 12.5 cm)
Lifespan	Up to 8 years in ideal conditions
Social Behavior	Peaceful, active shoaling fish (Keep in groups of 6 or more)
Water Type	Strictly alkaline/hard water
Conservation Status	Listed as Vulnerable/Endangered on the IUCN Red List (All aquarium specimens are captive-bred)

Aquarium Care & Tank Set-Up

Because Lake Kutubu is a highland, limestone-rich lake, replicating their unique natural chemistry is critical for keeping them healthy and vibrant.

Tank Size: A minimum of 55 gallons (or a tank at least 4 feet long) is highly recommended. They are fast, energetic swimmers that require plenty of open swimming room.
Water Parameters:
- pH: 7.5 to 8.5 (They will lose color and vitality in soft, acidic water).
- Temperature: 70°F to 80°F (21°C to 27°C).
- Hardness: dH 9 to 18.
Aquascaping: Use a layout featuring dense vegetation (like Vallisneria) along the back and sides, leaving the central area open. Bogwood and dark substrates help make their neon colors pop.
Filtration: They require pristine, well-oxygenated water. Weekly 50% water changes and a strong canister filter are ideal. [1]

Diet & Behavior

Diet: They are omnivorous. Provide a high-quality base of flakes or pellets supplemented frequently with live or frozen foods like brine shrimp, daphnia, and bloodworms to enhance their coloration.
Color Shifting: Their color is highly dynamic and changes with mood, hierarchy, and time of day. They display their most intense, breathtaking colors first thing in the morning or immediately after a water change.
Community Life: They are exceptionally peaceful and make great community fish. Despite their size, they have remarkably small throats and will not prey on smaller tank mates. Always maintain a ratio of multiple females per male to spread out amorous male energy and prevent stress.