Keeping Rainbowfish in the Aquarium

An edited version of this article was originally published in the November 2004 issue of Practical Fishkeeping magazine.
Introduction Rainbowfish are active yet peaceful fishes, which are hardy and tolerate a variety of different water parameters. As the name suggests, they often show spectacular colour. Hardy, active, colourful, peaceful… surely the perfect aquarium fish? Despite all these attributes, Rainbows are not as popular as many other commonly available fish. One of the main reasons for this is undoubtedly the lack of colour in juvenile fish. The juveniles of most species show only the barest hint of the wonderful colour they will display as adults. For this reason, they are easily by-passed as fishkeepers scan the tanks of their local store for a colourful and interesting addition to their aquarium.
Rainbows may also be a little more expensive than other familiar shoaling fish like the more common species of barbs and tetras - another reason why the relatively drab juveniles might be passed over in favour of more colourful alternatives. However, give these juveniles a year or two of the right care, and the stunning adult fish will more than reward the small extra expense.	Melanotaenia australis has become more commonly available recently.
The rainbows originate mainly from New Guinea and Australia, with a few species coming from Madagascar and Southeast Asia. The fishes of the family Melanotaenidae are regarded as the “true” rainbows. This family includes the largest genus, Melanotaenia, containing about 50 species, along with six other genera. In addition, members of related families such as the Pseudomugilidae (“blue-eyes”) and Atherinidae (silversides) are often included under the banner of rainbowfish.
Rainbows in the Aquarium Although the natural environment of rainbows covers a wide area, a temperature between 22-28oC (72-82oF) is suitable for most rainbows in aquaria, so a middle value of about 25oC (77oF) will be ideal for a mixed community tank containing them.
Rainbows come from natural waters with a range of different water chemistries. They appear to be extremely adaptable to varying hardness and pH values, as long as extremes are avoided. Most species will thrive in water from fairly soft and slightly acidic, to hard and alkaline. Species which originally come from soft, acidic water seem to thrive in harder water, and medium-hard, neutral to alkaline water is probably the best choice for most species of rainbows in aquaria.
Irrespective of their adaptability to different water chemistry, the water quality must not be neglected. Rainbows will show their best colours, and be more inclined to breed, in clean well-filtered water, with high oxygen content and minimal wastes.
This is probably best achieved using internal power filters for small to medium-sized tanks. These filters provide plenty of circulation (and hence aeration) and are good mechanical filters as well as providing biological filtration. In larger tanks (around 200 litres or 40-50 gallons or more), the combination of an internal power filter and an external canister filter would be ideal.
Wastes can be minimised with frequent water changes, and in general, rainbows seem to thrive on frequent large-scale water changes. In a mixed community tank, the needs of the other fishes will also influence the water change schedule, but for the rainbowfish themselves, weekly water changes of around 30% would be ideal. Rainbows are generally peaceful fishes, and although individuals can vary as with any fish, it is unusual to see aggressive behaviour, apart from the boisterous activity of male rainbows towards each other when spawning. They are shoaling fish and should ideally be kept in groups of five or more.
They are also fast-swimming and active fish, and for this reason the larger species may not be the ideal choice with timid or delicate companions, which may have difficulty competing for food. However, there are some smaller and less boisterous species available, see the notes on individual species below.
Suitable companions could include bottom feeders such as loaches and Corydoras catfish, as well as algae-eaters like Bristlenose catfish (Ancistrus species) or the true Siamese algae eater (Crossocheilos siamensis).
Rainbowfish sharing a planted tank with large Rasboras.	Other active mid-water or upper level shoaling fish like barbs, rasboras, danios and larger tetras should also get along fine with rainbows. Larger species of rainbows can be combined with many cichlids.
Rainbows are generally a good choice for planted tanks, and probably look their best when kept this way. Some species may nibble on soft-leaved plants. Artificial plants can of course be used as an alternative. Whichever is used, select a variety of colours and leaf shapes to provide a nice contrast, planting taller stem plants to the rear and small foreground plants near the front. Some pieces of bogwood or inert rocks will break up the aquascape and make it more interesting. Leave plenty of open swimming space at the front for these active fish. The larger species (10cm/4” or more) would be best housed in tanks no less than 122cm (4 feet) in length.
Most rainbows are not fussy feeders, and will accept most foods offered. However, this should not lead to complacency in providing a varied diet. Many rainbows feed primarily on insects and their larvae in the wild. In the aquarium, a range of flake, granular and pellet foods can be offered, supplemented with plenty of frozen and/or live foods.

Commonly available species of Rainbowfish The genus Melanotaenia contains many of the commonly available species. These include Boeseman’s rainbow (M. boesemani), the Banded rainbow (M. trifasciata), the Lake Kutubu rainbow (M. lacustris), and the Dwarf Neon rainbow (M. praecox).
The popular Boeseman’s rainbow shows a distinctive contrasting half-and-half colouration of steel-blue on the anterior (front) half of the body, and a golden-orange colour on the posterior. They originate from Irian Jaya (the western half of New Guinea) which is part of Indonesia. Like the other species covered here, the fish in the hobby are likely to be farm bred. Adults reach about 15cm (6”) maximum.
The Banded rainbow is a truly stunning fish as an adult, with orange/red coloured fins and a myriad of greens, golds and other colours displayed in the body. There are literally dozens of colour variations arising from different geographical areas of its range in northern Australia. Some of these also exhibit differences in size and body shape, and might eventually be described as subspecies or new species. Adult size is 10-15cm (4-6”).
The Lake Kutubu rainbow, sometimes called the turquoise or blue rainbow, is another species which exhibits stunning colour as an adult. The upper half of the body shows beautiful blue or blue-green colouration, and the lower half is usually silvery-white to gold. However, like many rainbows, this species is capable of changing its colouration quite rapidly. This species is found only in Lake Kutubu and its tributaries, in Papua New Guinea. This slightly smaller species reaches about 10cm (4”) maximum.
A smaller member of the Melanotaenia genus is the Dwarf Neon rainbow, Melanotaenia praecox, sometimes known simply as the praecox rainbow, which attains about 5cm (2”). Its smaller size and peaceful nature make this species a good choice for smaller community tanks with other peaceful tankmates. Their silvery bodies exhibit a wonderful neon blue sheen, which catches the light quite spectacularly. The fins of males are deep red, whereas the females have yellow-orange fins – this difference is apparent even in young fish.
Other relatively common representatives of the large Melanotaenia genus are an old favourite, the Dwarf Australian rainbow (M. maccullochi) and the Splendid rainbow (M. splendida), which has a number of subspecies.
The Red rainbow, Glossolepis incisus, is by far the most commonly encountered of its genus. The stunning red colouration of adult males has ensured their popularity. Juveniles and females are a silvery yellow-brown colour. This is another species hailing from Irian Jaya, which reaches about 15cm (6”) in length. They are suited to medium to large display aquaria with plenty of open swimming space.
The Threadfin rainbow, Iratherina werneri, is a little different to the other species covered here and the only member of its genus. They are smaller and more delicate fish which are best kept in either a species tank or with a few peaceful companions such as Corydoras catfish and peaceful tetras like Neons, Glowlight tetras or Rummy Nose tetras. They should never be mixed with any fish with the potential to fin-nip, as their long and delicate fins would be an obvious target. This species comes from northern Australia and the Irian Jaya, and reaches about 5cm (2”). Males are slightly larger and have dramatic extensions to their second dorsal and anal fin. Despite their delicate appearance, they should prove relatively hardy fishes once established in the aquarium.
Although not as commonly encountered as the species mentioned above, Bedotia geayi, one of a small number of rainbowfish from Madagascar, is occasionally available. It is slimmer in shape than the Melanotaenia species, and attains 8-9cm (approx 3-4”) in length. The species normally encountered in the hobby may actually be B. madagascariensis rather than B. geayi.
For smaller tanks, two other groups are worth mentioning and will provide interesting little subjects for the enthusiast. The first of these is the “blue-eyes” (Pseudomugil species), many of which are at least partially brackish in their natural environment. The other is the Celebes rainbow (Marosatherina ladigesi or Telmatherina celebensis) and related species, originating from the island of Sulawesi (formerly Celebes).

Breeding Male rainbows generally display brighter colours, and in most species mature males have noticeably deeper bodies. Additionally, the first dorsal fin is longer in males of most species, and tends to overlap the second dorsal fin when laid flat. Rainbows will display their most impressive colours when ready to breed, and they are not generally difficult to spawn in the aquarium. If you intend to breed rainbows, you should avoid keeping similar species of the same genus together, or mixing subspecies or regional variants, to avoid creating hybrid fish. Promoting vigorous health with a good diet and high water quality is the most important step towards encouraging the fish to spawn. Rainbows commonly spawn in the morning, and the lighting used in and around the tank could have a strong influence on spawning. A little morning sun dappling the water may prove an effective trigger, though even the flash from a camera has been reported to trigger repeated spawning events! At their peak breeding age, rainbows will spawn on a fairly constant, even daily, basis.
A group of spawning rainbowfish is a spectacular sight. Males dash about with short bursts of speed and then stop suddenly, extending their fins fully in an impressive display to the females. It is possible to breed rainbows as pairs, harems or larger groups. Due to the fact that males chase each other around as they display in front of the females, it’s best to have at least three males in a potential breeding group, so that it’s not simply a case of one male dominating a second male. Because the males usually chase each other in this way rather than directly harassing the females, a breeding group can consist of three or more males and two or more females. In pairs, males can sometimes become quite aggressive when attempting to drive a reticent female towards the spawning site.
Rainbowfish will tend to eat both eggs and fry after spawning. “Unplanned” spawning in the display or community tank may produce a few surviving fry if they have plenty of cover to hide in. However, if you wish to raise as many fry as possible, you will need to spawn the adults in a separate aquarium, and remove them after spawning – or remove the spawning substrate.
A spawning/rearing tank should be kept simple. No substrate is necessary, and a bare glass bottom will make siphoning off debris easier. Provide a heater and a pre-matured sponge filter. Do not use power filters in fry tanks, as the fry may get sucked into the filter. Provide artificial spawning mops (usually made with strands of wool) or fine leaved plants such as Cabomba, Myriophyllum or Java Moss. Adhesive eggs will be scattered during the spawning process. The eggs take about a week to hatch.
The fry are very tiny at first and infusoria/green water or commercial liquid foods are ideal for the first week or two. Cultures of infusoria (various microorganisms) or green water can be created by simply leaving a jar of aquarium water on a windowsill in direct sunlight for a week or two. Various additions are sometimes suggested including a slice of banana or potato peelings. A small amount of this culture is then poured into the water, as close to the fry as possible (alternatively, a small plastic dropper/pipette can be useful). Newly hatched baby brine shrimp makes an ideal second-stage food, which can be combined with powdered fry foods. Microworms are another alternative, and are easy to culture. Smaller frozen foods such as Cyclops are also useful in the early stages. Simply crushing flake, etc intended for adult fish is not ideal, as the nutritional needs of young fry are different; however, this approach can be used with older fry. Ideally, fry should be fed small amounts at least 2-3 times per day. Any uneaten food and wastes should be siphoned off regularly. At a normal growth rate, fry should be sexable by the time they reach 3 months old. Between 6-12 months they will become sexually mature and able to breed themselves.

This article Copyright © 2004 Sean Evans. All rights reserved.

 

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