Turquoise Rainbowfish

With the iridescent turquoise-blue color of its body, the turquoise rainbowfish has the brightest blue of all rainbowfish. It is endemic to Lake Kutubu in the highlands of Papua New Guinea, and because its natural habitat is limited to a single lake, it is considered a vulnerable species. Fish in the aquarium have long been obtained through captive breeding.

It is a fast-swimming fish that reaches 11–12 cm. Its blue tones change with age, light and mood; the backs of displaying males turn navy blue. Juveniles are silvery and dull, and the real colors appear over a few months.

Lake Kutubu is a clear lake set in limestone terrain about 800 m above sea level. Its water is moderately hard and slightly alkaline; because of the altitude it is somewhat cooler than the waters of the tropical lowlands. The fish live along the lake's planted shores and in the stream that flows out of it.

• Volume: at least 200 liters and 120 cm of length for a school of 6–10.
• Water: 23–26°C, pH 7–8, moderately hard water. Stable, clean water matters more than high temperature; do a 25–30% water change every week.
• Decor: Dense plants and roots along the edges, with a wide open swimming area in front.
• Lighting: Good lighting and a dark background make the turquoise shine.
• Lid: A good jumper; the lid must be tight.

Omnivorous and greedy. It feeds on quality flakes and granules, frozen brine shrimp, mysis, bloodworms and daphnia; give a spirulina-enriched food several times a week. Feed small amounts often; overfeeding leads to bloating and poor water quality.

Peaceful but very energetic. Males display to each other with spread fins in the mornings, and a light-colored line appears on their foreheads. It outcompetes small and slow fish at feeding time; it eats baby shrimp and small shrimp.

Good companions: Large rainbowfish from other genera (e.g. the red rainbowfish), Congo tetras, rosy barbs, corydoras, synodontis, bristlenose plecos (Ancistrus), loaches (botias).

Avoid: Neocaridina shrimp, slow long-finned fish, aggressive cichlids; other Melanotaenia species if you plan to breed.

At least 6, ideally 10 or more individuals. A group set up with 2 females per male is balanced; several males displaying to each other bring out the turquoise color at its most intense. Fish kept singly or in pairs stay shy and pale.

A continuous-spawning egg scatterer. Pairs lay a few eggs every day in the morning hours on fine-leaved plants, Java moss or a wool spawning mop; the eggs attach with sticky threads. Because the parents eat the eggs, move the mop to a separate container regularly. The fry hatch in about 7–12 days; they are first given infusoria and liquid fry food, then newly hatched brine shrimp.

Hybridization: It hybridizes easily with other Melanotaenia species, especially similar-sized species in the same tank. To preserve a pure line, breed the species separately and do not distribute hybrid offspring.

• White spot: Can appear after sudden drops in temperature; keep the temperature stable.
• Bloating: Seen with overfeeding and a monotonous diet; one fasting day a week helps.
• Color fading: The first sign of stress and poor water.
• Generally hardy; it lives long in clean, stable water.

Males are larger, deeper-bodied and far more intensely turquoise; during display their backs turn dark navy. Females are smaller, slimmer and greenish-silver, with paler, shorter fins.