A Rainbow in the Tank

A Rainbow in the Tank

Those of us who live in areas where the kettle is permanently coated with a layer of white fuzz and you need half a bottle of shampoo to get a few bubbles may well look at all the pretty discus and their cousins in the shop, but know that our hard water is likely to see them turning up their fins in a very short space of time. With suitable investment, it is possible to clean water in a hard water tap area to soft, or you could collect rain water, which poses its own problems when you live under a major flight path, but overall the easiest solution is to choose fish that will put up with it.

This isn't as bad as it may seem. All the popular tough customers in the fish shop have already been acclimatised to the water, so don't pose any problems transferring from shop to tank. However, if you like to see little fish families appearing, it becomes a much greater consideration. Many fish that will tolerate living in water that is not their natural water chemistry will not even consider spawning in it. If they try, eggs are far more sensitive to water chemistry and often will not hatch. Guppies, of course will breed anywhere, and so will some of the other more common fish. But for something a little different hard-water area dwellers may have to give the matter a bit more consideration. Gobies are generally quite good (with the exception of the beautiful but soft-water peacock goby) as even the freshwater ones are only a short step away from being brackish-water fish. They do, however, tend to be rather brownish, or at least those that show up with any regularity in the shops do. What if you want something a little better-looking? Fortunately there is a family of fish which are certainly no slouches in the beauty stakes, are generally quite hardy, a reasonable size and usually very active. Next time you are in the shop, take another look into the tanks of rainbow fish. These are streamlined, slightly flattened fish native to Australia and New Guinea, where they inhabit streams. Each stream can have its own variant or species, which means there is a huge range of fish to choose from (although it may be a while before you can get the ones you want and it may be as well to choose several 'possible' species before you go shopping). All are striking, attractive, and relatively small. Wild species seldom grow over four inches, and although aquarium specimens can grow a bit bigger with a good and regular diet, they are never going to turn into huge fish.

One of my favourites is the Lake Kutubu rainbowfish, Melanotaenia lacustris. These are a beautiful deep metallic blue, with a brilliant yellow stripe up from the nose along the dorsal edge to the dorsal fin and more yellow along the sides. From Papua New Guinea, they prefer water on the hard side of neutral, with a recommended pH of 7.3. Growing up to just under four inches, they are a manageable size for most community aquaria. They like lots of plants and driftwood, but a good open swimming space is needed, as they do like to zoom around when the mood takes them. They are peaceful and friendly fish which quite happily coexist with each other, other rainbowfish, and other community fish. They are, in my opinion, one of the most beautiful fish available for the aquarium, although they don't always show their best colouration in a busy shop.

Another eye-catching fish is Boeseman's rainbowfish, Melanotaenia boesemani, also at around four inches. The male looks as though he cannot possibly have gained his colouration naturally, looking rather like two halves of different fish spliced together. The front end is a dark blue, while the rear end is a rich orange. In some of these fish the division between the two colours is blurred, but in others it is a sharp delineation. The females are more sombre, being a silvery pale green.

For a smaller aquarium, consider the Dwarf rainbowfish, Melanotaenia praecox. These are also an iridescent blue, but the males have brilliant scarlet fins. At only two inches each, a little group of five or so won't take up too much aquarium space. Like the other fish mentioned these are peaceful and friendly - if anything they are a bit on the shy side and can be bullied by boisterous tankmates.

Also small, although slightly large than the dwarfs at about three inches, is the Celebes rainbow. Telmatherina celebensis is from a different family, but just as good to keep as its Melanotaenia cousins. The fish will happily live in water with a pH of up to 8.3 - in fact, they will be happier in a community with some salt added to the water and some brackish companions, rather like the bumblebee goby which also usually appears in the freshwater section but is happier with salt added (In fact, the two make good tank compatriots). Although they will prefer harder water, they are very sensitive to changes in the water chemistry, so if you plan to make a change form the conditions they were in when you bought them it must be done very slowly, bit by bit. The Celebes rainbowfish likes the same sort of setup as the others, with plants to hide in and some open swimming space. These are also very striking fish. There are two dorsal fins. The first is very small, but the first rays of the second develop into long threadlike trailing tendrils, as with the anal fin. These extensions are longer in the male than in the female. They are mostly yellowish, with black leading edges to the fins and an iridescent blue-green stripe stretching along the flank.

Although they are quite tolerant of water chemistries, they aren't tolerant of water pollution (as is true of most fish) so make sure the water is clean and well-maintained. They will appreciate a good current to swim around in (if you direct a filter output along the front of the tank this leaves it a bit quieter at the back). They aren't fussy feeders, and will quite happily devour flake, but you will be missing out on half the fun if you don't give them live food. A bag of daphnia will soon have the fish chasing energetically in all directions. This works with frozen daphnia or bloodworm too - just drop it in the filter current so that it blows round the tank. They are surface and midwater feeders, who won't have much interest in food that has sunk to the bottom. With all these conditions met for happy and healthy fish, their concerns will soon turn to starting a family. A little group is best - the males can be a bit boisterous, so their attention needs diverting. If you have two males and a female the males will chase each other some of the time. Two females and a male is another possibility, but most people prefer the brighter males. To spawn your rainbow fish successfully you ideally need some floating plants, but failing that you can make a little floating mop with a cork and a ball of wool - it's not the most natural décor, but the fish won't mind at all. They like to spawn at dawn and dusk, so if they are a bit stubborn then creative use of lighting might encourage them - most fish tanks get lights on or lights off, with very little transition between. Once they start chasing in earnest, little round eggs will be deposited in the mop or plants, where they will stick. This is a good time to transfer your mop, or plant, with its attached load of eggs, into your prepared fry tank. Little rainbowfish look very like live food, and in the main tank the odds of their survival are low. Once the eggs hatch you can feed the fry on proprietary foods, and baby brine shrimp will help encourage them to grow - although not much. This is the only real drawback of rainbowfish - they are incredibly slow-growing. Spawns of other fish will have come, reached full size and gone, while your little rainbowfish brood grow imperceptibly. This is one of the reasons they tend to be on the expensive side in shops - it's not that it's hard spawning them, but rearing takes a long time.

Although rainbowfish do cost that little bit more, they are an investment well worth making. There's one of a suitable size for most communities (and some brackish ones, like the Celebes mentioned here), and their addition will always guarantee both beauty and activity in your tank. With a limited space in this article it is possible to only skim the surface of the variety of rainbowfish; there are plenty more of a similar disposition than those mentioned here. Their appearance in the shops is rather haphazard and unpredictable though, so once you've made out your candidates list it might take a while before you find one in a shop. If you really can't find them or your aquarium shop is unhelpful, the Rainbowfish and Goby society will generally be pleased to help.


This article has been kindly provided by Kathy Jinkings and cannot be reproduced without her permission.

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