Often overlooked as 'dull silver fish' in shop tanks, rainbow-fish develop their color as they mature and are amongst the most robust and colorful fish available for the aquarium
Everyone must know the story of the ugly ducking who felt left out and dejected until one day upon seeing its reflection, saw the image of the beautiful swan he had become. This could also be the story of the rainbowfish - those dull silvery fish with high price tags you may have seen for sale. One day these fish will become the most colourful fish in their aquarium and the pride of the plucky aquarist who purchased them. In fact, rainbowfish have quiet a lot going for them which may not be apparent at first glance
Rainbowfish are a large group of fish from varied natural environments, In fact there is a rainbowfish suited to almost every aquarium setup. For the purposes of this article we will concentrate on the true rainbowfishes from the family Melanotaeniidae
In evolutionary terms, the true rainbowfish are a very young family of fish being only around 200,000 years old. For the vast majority of this time the land they occupied around Australia and New Guinea was undergoing a continual changing of environment.
The young rainbowfish family are therefore still rapidly evolving and this can be seen today in the large variations of colour forms within the same species.
At some point it is likely that these regional variations will become different species. For the fishkeeper, this means that identifying rainbowfish can become very tricky without the help of a comprehensive guide of species and colour variations.
Its all in the genes
Even within the true rainbowfishes there is such a variety of natural habitats that it would be difficult to generalise ideal aquarium conditions if it were not for the fact that rainbowfish are incredibly adaptable and lend themselves so well to the aquarium.
It is common knowledge amongst aquarists and good retailers that rainbowfish generally prefer harder water conditions, however this does not always mimic their natural environment. Whilst rainbowfishes from New Guinea almost always come from moderately hard water with pH values typically between 7-8, rainbowfishes from Australia almost always come from soft acidic waters.
Because the group are only recently evolved from marine species, those that are found in soft water have a much greater adaptability to hard water than you would see in other softwater species. All rainbowfish will do well in hard water but if you have a softwater aquarium, do a little research and you will find that many common rainbowfish are also ideally suited to softwater.
Both Australian and New Guinea rainbowfish experience a wide range of natural water temperatures. In Australia, the temperature difference is dictated by regional differences whilst in New Guinea differences occur based on the altitude that the fish may be found.
It is not uncommon to find rainbowfish in waters as low as 12C or as high as 30C depending on where you find them. In the aquarium most will do best at a normal temperature of between 24-26C, but once again do a little research and you will find rainbowfish well suited to unheated temperate aquaria.
Exploring new surroundings
Most rainbowfish come from open rivers with little vegetation or lakes so planting is not as important in the aquarium as open swimming spaces with hiding spots amongst roots. A few plants and dense patches around the edges of the aquarium will still benefit the fish.
Rainbowfish also find comfort in being in groups so at least five or six should be kept together, although they do not always have to be the same species it is best to make groups up of similarly shaped and sized species.
Rainbowfish are all very peaceful active swimmers and will mix with most community fish. Most rainbows can get to a reasonable size of between 10-15cm (4-6") so very small tankmates should be avoided and a minimum tank size of at least 90cm (36") is essential.
The futures bright
When young most rainbowfish do not show a fraction of their adult colour, so they are often missed by fish-keepers and remain in the shop tanks until a more experienced aquarist purchases them or the staff quite rightly persuades someone to purchase them.
This low turnover means their price remains relatively high and you may have to search a little for a greater variety of species, but at an average price of around £6 a piece I would still consider them a worthwhile investment. Rainbows are generally very hardy but it is still worth checking for good health before purchase. It is especially worth checking for ulcerations which rainbowfish can be quite prone to when they are moved around different environments.
For more experienced aquarists or those looking for a good challenge, breeding rainbowfish can be a satisfying achievement. Sexing rainbowfish is tricky at best and sometimes impossible with young fish. In adults males have elongated dorsal fins, are often more prominently coloured and sometimes display an intermittent stripe across the top of the head to the dorsal fin.
Rainbowfish are permanent spawners which means they can continually spawn, sometimes daily throughout their adult lives. To encourage successful spawning you can try avoiding water changes for a while then carrying out a moderately large water change and also allow some sunlight to reach the aquarium. If the rainbows are allowed natural sunlight in the morning, this often encourages mating displays and is a great way to see your fishes best colours.
When the fish are ready they will spawn easily and should be provided with some spawning mops or dense finely leaved vegetation such as some cabomba or Java moss in which to drop their eggs. Eggs normally hatch after 5-7 days and the young can be fed on the usual newly hatched brineshrimp, live daphnia, crushed flake and vegetation.