Rainbowfish Species: Why They Look Dull in the Shop
Rainbowfish are sold as juveniles before their colour develops, which is why they look grey in the shop tank. Which species to pick, and what they need to colour up.
The photograph problem
Rainbowfish have the widest gap in the hobby between what the fish looks like in the shop and what it looks like in two years. They are sold as juveniles, and juvenile rainbowfish are grey-silver with a hint of what is coming. The photographs that sell them are of mature males in breeding condition.
This costs the group sales it should win, and it also causes the most common disappointment: someone buys three, keeps them in a quiet tank, and the colour never arrives. Colour in rainbowfish is a function of maturity, of being in a group, and of having something to display against.
The species compared
Reading that table
Size is the first filter, and length is the real constraint. The dwarf species stay around 5-7cm; the larger Melanotaenia reach 10-12cm and are strong, constant swimmers. For this group the footprint of the tank matters more than its volume — a long tank of modest depth suits them better than a tall one holding the same litres.
Not everything called a rainbowfish is closely related. The Celebes rainbowfish comes from Sulawesi rather than Australia and New Guinea, and the forktail is a blue-eye rather than a Melanotaenia. They are grouped by appearance and by trade convention, so check the individual profile rather than assuming the water and the adult size carry across the group.
They are hard-water fish more often than not. Many of the Australian and New Guinean species come from neutral to alkaline water, which puts them at odds with the soft-water tetras and rasboras they are often stocked alongside. It is not usually fatal — they are adaptable — but it is worth checking against your tap water before committing.
Getting them to colour up
Four things, in rough order of effect:
Keep enough of them. Six is a floor, not a target. Males colour when they have rivals, and a single male in a peaceful tank has no reason to.
Give them time. Full colour takes months, sometimes more than a year in the larger species. The fish you bought is not the fish you will have.
Feed properly. Varied food, including live or frozen, shows in the colour of this group more visibly than in most.
Give them a dark substrate and some plants. Rainbowfish wash out over bright gravel, and the contrast of a planted tank does half the work before the fish has done anything.
Where to start
The dwarf neon and the Boesemani-type species are the usual entry points: widely available, hardy, and colourful enough at a size that suits a normal community tank. The Celebes rainbowfish is the outlier worth knowing about — smaller, more delicate, and a different fish from the rest of this list.
Individual profiles below cover parameters, sexing and breeding for each species.
