Rainbowfish is a name used for the small and colorful found in the family Melanotaeniidae within the order Atheriniformes. The largest genus within this family is Melanotaenia. The name is derived from the word “melano” which means black in Ancient Greek and “taenia” which means ribbon. This is an aptly chosen name, since Rainbowfish species within the genus Melanotaenia display black markings on the soft dorsal and anal fins.

Rainbowfish species are small and very colourful and therefore popular in freshwater aquariums. They originate from Australia and New Guinea and are also found on a few nearby islands. In the wild, the Rainbowfish populations have been decimated since the Mosquito fish, Gambusia affinis, was introduced to this part of the world.

Rainbowfish is considered very easy to keep in aquariums and is recommended even for beginners. They can be kept in aquariums with live plants without harming the plants, and unlike many other fish species they will not dig around in the bottom substrate. They are all comparatively small which means that they can do well even in a smaller aquarium, as long as the aquarist is skilled enough to keep the water levels up. The aquarium should however always be at least 45 centimetres wide and must contain plenty of surface area. Rainbowfish do not swim vertically, they swim horizontally, and the surface area is therefore more important than the depth of the aquarium. The Rainbowfish will spend most of its time at the surface or in mid-water in the aquarium. When you decorate the aquarium you should leave some open spaces for the fish to swim around in. If you are a novice aquarist, a larger aquarium is recommended since a large aquarium is much easier to maintain than a small one. Since the maximal size of each Rainbowfish species vary, you must always research the particular species that you are interested in to find out how much space it requires.

The Australian and New Guinean waters where your can find Rainbowfish are usually soft, which means that you might need to adjust your tap water if it is hard. The pH varies from habitat to habitat and the best way of finding out the ideal pH for your Rainbowfish is therefore to find out exactly where it lives in the wild. Generally speaking, a Rainbowfish can live in a pH between 6 and 9, but this does not mean that any of the extremes are ideal for it. If the pH goes below 6 or beyond 9, one of the first signs will be stunted growth. As the pH drops below 4 or goes up above 10, the Rainbowfish will die.

Melanotaenia boesemani, a common rainbowfish.
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The water temperature should be between 20 and 24 degrees Celsius when you keep Rainbowfish. If you want to coax your Rainbowfish into spawning, you can increase the water temperature up to 28 degrees Celsius. In the wild, Rainbowfish can be exposed to temperatures ranging from 5° C up to 35° or even more. Such conditions are however far from favourable for the Rainbowfish and they should definitely be avoided in the aquarium.

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