Rainbowfish

Schooling fish from New Guinea whose colour depends on water and food. Shy, jumpy and always on the move.

Melanotaenia · Other · Reference · updated 11 November 2026

What it is and where it comes from

Rainbowfishes are the genus Melanotaenia, family Melanotaeniidae, with more than fifty species. Home is New Guinea and northern Australia, where they live in lakes, streams and swamps. Boeseman's rainbowfish is known only from the Ajamaru lakes in Irian Jaya, the neon from the Mamberamo system. Lake water there is hard and alkaline, up to pH 9, yet some populations hold on in soft tributaries at around pH 6.

In tanks you mostly see Boeseman's, neon and three-striped. Nearly all are farm fish from South-East Asia and Eastern Europe; wild specimens are practically absent from the trade. Boeseman's is rare and on the Red List in nature, and more numerous in aquariums than at home.

Housing and conditions

Requirements depend on the species: the neon rainbow likes 23–28 °C, Boeseman's prefers 27–30. The overall range is 23–30 °C, pH 6.5–8.0, hardness 5–20 °dGH. Boeseman's takes soft acid water badly, so hardness and a stable pH matter more to it.

From 100 l for the large species, on a base of 120 by 30 cm; small ones do in 60–80 l. Moderate current, good aeration, bright light with shaded patches. Dense plants along the sides, open water in the middle. The lid must fit tightly, because these fish are shy and jump at a sudden light or a knock.

Feeding

Omnivores: flakes, granules, frozen bloodworm, brine shrimp, daphnia. Feed twice a day in small portions, one or two minutes per meal. Colour follows the diet, and without live and frozen food the fish pales, males first.

Overfeeding shows as a heavy belly and lethargy, followed by obesity, breathlessness and a refusal to feed. A fasting day a week suits adults; fry and juveniles are never restricted.

Lifespan

Usually five to eight years. Exact figures per species are rarely published and the spread in the sources is wide: small species live less, large ones more. Boeseman's matures slowly and reaches full colour only by two years.

Temperament and tank mates

Peaceful and very fast. In a school of six to eight they are bolder, and the males display colour at each other all day. They get on with slow neighbours but startle them with sudden darts.

• good: danios, barbs, large tetras, corydoras, labeo;
• avoid: large cichlids, veil forms, small shrimp;
• a school of six or more, otherwise stress and pale colour.

Diseases

The usual set for an active schooling fish:

• Ich. White spots, rubbing against plants. Treat with malachite green.
• Oodinium. Golden dust and mucus, the fish hanging near the surface.
• Fin rot. Ragged fins after fights or in dirty water.
• Injuries. Strikes against glass and lid when startled, torn lips.

A vet makes the diagnosis; guessing with antibiotics does harm.

Breeding

Spawning is easy: these are egg scatterers that care for nothing afterwards. A tank from 40 l, water at 24–27 °C, pH around 7.5, moss or a synthetic mop instead of gravel. A pair spawns daily for weeks and the eggs hang on threads. Move the eggs to a separate tank; incubation takes 7–12 days, and the fry start on infusoria before moving to brine shrimp nauplii.

Who it suits

A beginner, given 100 l and the wish to keep a school. The fish is hardy, eats anything, does not dig and leaves plants alone. Weak points: shyness, jumping, price, and the slow colouring of Boeseman's. The strong side is movement in the upper layers and colour you can see across a room. The calculator shows how many rainbowfish a tank will hold.

Calculator

The calculator takes your dimensions and works out glass, weight, stand and doses.