Lake kutubu rainbowfish - Melanotaenia lacustris

Scientific name: Melanotaenia lacustris

Common name: Lake kutubu rainbowfish

Family: Melanotaeniidae

Usual size in fish tanks: 11 - 13 cm (4.33 - 5.12 inch)

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Recommended pH range: 7.4 - 8.4

Recommended water hardness: 10 - 18°N (178.57 - 321.43ppm)

0°C 32°F30°C 86°F

Recommended temperature range: 24 - 27 °C (75.2 - 80.6°F)

The way how these fish reproduce: Spawning

Where the species comes from: Oceania

Temperament to its own species: peaceful

Temperament toward other fish species: peaceful

Usual place in the tank: Middle levels

General Information

The Lake Kutubu Rainbowfish (Melanotaenia lacustris) is a robust, schooling rainbowfish endemic to Lake Kutubu and its outlet (Soro/Kikori system) in Papua New Guinea. Adults commonly reach 11–13 cm in aquaria. In nature they inhabit very clear, still to slow waters with aquatic vegetation, submerged roots and logs, congregating mid–upper water. Note: the species is assessed as Endangered (IUCN); choose sustainably sourced stock.

Food & Feeding

Omnivore. Use quality spirulina/algae-rich flakes or small pellets as the staple and rotate frozen/live foods (daphnia, Artemia, mysis; bloodworms in moderation). Offer small portions 1–2× daily to maintain water quality and colour without overloading filtration.

Sexing

Males develop deeper bodies with more intense turquoise/blue and reddish/orange in the fins; females remain slimmer and paler. Juveniles look similar until maturity.

Breeding

A classic egg-scattering, plant/mop spawner that will deposit small adhesive eggs over days rather than in one event. For controlled spawning, use spawning mops or fine-leaved plants in a separate, dim tank. Remove mops/eggs or the adults post-spawn. Eggs typically hatch in ~7–8 days (temperature dependent); start fry on infusoria/microfoods, then newly hatched brine shrimp. Avoid messy egg-yolk feeds.

Lifespan

Commonly 5–8 years with excellent water quality, oxygenation and a varied diet.

Tank Requirements & Water Parameters

Tank size: active shoaler—use a long tank of at least 120 cm / 4′ for a group (6–8 ), with open lanes and planted margins.
Water chemistry (key): prefers hard, alkaline water. Lake Kutubu itself runs about pH 7.6–8.1 with measurable mineral content; aim for pH ~7.4–8.4, GH/KH in the mid–high range. Stability matters more than the absolute number.
Temperature: 24–27 °C (75–81 °F) is ideal; tolerates roughly 21–25 °C on the cooler side.
Filtration & flow: strong biofiltration and oxygenation; minimal to moderate current to mimic clear lake conditions.
Aquascape: plants, wood/roots and smooth rock with large open water zones; tight-fitting lid recommended for lively shoals.
Maintenance: weekly water changes; avoid abrupt parameter swings.

Compatibility & Tank Mates

Peaceful, fast-moving shoaler. Keep in groups of 6–8 to show best colour and reduce sparring. Suitable with other medium rainbowfishes, robust rasboras/barbs, larger tetras, and peaceful catfishes. Avoid tiny, very slow or long-finned species that may be stressed by activity.

Behaviour & Usual Place in the Tank

Occupies the middle (to upper) water column and appreciates strong light and clear water for display; retreats among plants and wood when startled.

Short Description

Lake Kutubu Rainbowfish is a striking, endangered PNG endemic that thrives in hard, alkaline, clear water with space to school. Provide a long tank, stable high-quality water, a mixed omnivorous diet, and spawning mops if you wish to breed them.