Turquoise Rainbowfish, Melanotaenia lacustris, is a large rainbowfish native to Papua New Guinea. Its natural distribution is centered around Lake Kutubu and the nearby Soro River drainage in the Southern Highlands region. These waters are clear, warm, and well oxygenated, with moderate vegetation, submerged wood, and open swimming areas typical of upland lake and river systems. Adult Turquoise Rainbowfish typically reaches about 4 to 5 inches in length. The body is deep and laterally compressed with large reflective scales that give the fish a metallic appearance. Mature males develop an intense turquoise to blue-green coloration across the body, often with darker edging on the scales that creates a subtle reticulated pattern. The dorsal and anal fins are elongated and may show yellow to orange highlights. Females remain slightly smaller and less intensely colored, usually displaying softer blue-green tones. A tank of at least 55 to 75 gallons is recommended for a proper group. Turquoise Rainbowfish is a schooling species and should be kept in groups of six or more to encourage natural behavior and reduce stress. The aquarium should provide long open swimming areas with plants, driftwood, or rocks arranged along the edges. Moderate water movement and strong filtration help replicate their natural habitat and maintain high water quality. Water conditions should remain stable and clean. Temperatures between 74 and 80 degrees Fahrenheit are appropriate, with a pH range of roughly 6.5 to 8.0 and moderate hardness. Turquoise Rainbowfish are adaptable but perform best in well-maintained aquariums with regular water changes and good oxygenation. Feeding Turquoise Rainbowfish is straightforward. In nature they feed on insects, small crustaceans, and other aquatic invertebrates. In the aquarium they readily accept high-quality flakes, pellets, and frozen foods such as brine shrimp, bloodworms, and daphnia. A varied diet enhances coloration and supports strong growth. Temperament is peaceful but energetic. Turquoise Rainbowfish does well with other similarly sized, non-aggressive fish that can tolerate their constant activity. Suitable tankmates include other rainbowfish, larger tetras, peaceful cichlids, and robust catfish. Very small fish may be intimidated by their size and speed. Breeding is possible in captivity. Like other rainbowfish, they are egg scatterers that deposit adhesive eggs among fine-leaved plants or spawning mops. Adults do not provide parental care, and eggs or fry should be removed if breeding is desired. Melanotaenia lacustris, the Turquoise Rainbowfish, is a striking and active species that becomes a centerpiece in larger aquariums. With ample swimming space, clean water, and a varied diet, it rewards aquarists with brilliant turquoise coloration and constant schooling movement.
