• Scientific name: Melanotaenia lacustris
• Synonyms: Blue Rainbowfish, Turquoise Rainbowfish
• Common name: Lake Kutubu Rainbowfish
• Group: Rainbowfish
• Habitat: Asia; Papua New Guinea
• Size: 12 cm
• Biotope: Lake Kutubu and the River Soro, which flows out of the lake.
• Social behavior: A peaceful active shoaling fish. They can be skittish and does far better when kept in a small group. Can be kept in a species aquarium or be combined with other non-aggressive species of similar size.
• Diet: Omnivorous; They accept most foods including pellet and flake as well as live/frozen foods such as bloodworm and brine shrimp.
• Breeding: Quite easy
• Tank: Minimum 110 litres
• Population: 6-8 fishes for 200 litres
• Decoration: Provide areas of dense vegetation, along with some open areas for swimming. Water movement should be kept to a minimum.
• Temperature: 20-25 °C
• pH: 7-9
• Hardness: 10-20 NK°
• Lifespan: 5-8 years

Description: Lake Kutubu is the 2nd largest lake in Papua New Guinea (50 km²), and was formed when debris from an erupting volcano blocked off a valley. The water of Lake Kutubu is clear, and the lake reaches a depth of 70 m. The surrounding environment consists of limestone and the water in the lake is really alkaline with a pH-value of 8.5-9.0. Wild populations of the fish are being decimated by over harvesting and environmental destruction. The Lake Kutubu Rainbowfish is listed as “Vulnerable” on the IUCN Red List of Threatened Species. Their body is long and it deepens as the fish ages. The body of the fish is usually blue to on top, and fade through green to silver or yellow on the bottom. From the base of the tail, the fish has a dark blue stripe that disappears around the middle of the body. The fins are light blue, and may show black edges. Lake Kutubu Rainbowfish have the ability to change their colors quickly. Mature males are larger and have brighter colouration than females.
The breeding aquarium should be at least 80 cm long and contain slightly hard, alkaline water (pH 7.5) and a temperature of 23-24°C. The tank should be filled with fine-leaved plants such as java moss. Before spawning condition the males and females in a separated tank with live and frozen foods. The males develop an orange patch above their gill flaps, and the females become plumper. At this point select the best colored pair, and put them into the spawning tank. The pair will spawn for a period of several weeks, laying batches of eggs each day. After spawning the eggs should be removed, as the parents are egg scatterers. The number of the eggs can be 200. The eggs hatch after 7-12 day, which depends on the temperature, and should be fed infusoria or a liquid fry food until they are able to eat small live foods. Sinking pellet foods are not good, as the fry usually stay very close to the water surface. A fairly slow growth rate is perfectly normal, even for fry kept in ideal conditions. A fairly slow growth rate is normal, even for fry kept in ideal conditions.