Introduction

Almost all rainbowfishes sold in the aquarium hobby today are bred in captivity. This is due in the main to the difficulties involved in collecting and transporting live rainbowfishes from their natural habitats in remote areas of Australia and New Guinea. This is even more relevant in New Guinea where dense rainforests, virtually no infrastructure like roads and airports has meant that organised collecting for the aquarium trade is just simply not possible. Most rainbowfish species that have been introduced to the aquarium hobby has been by various private collectors. Rainbowfishes spawn readily in captivity and there are now large captive populations that satisfy most of the demands for the hobby, thus negating the need for wild-caught fish. There is probably some limited collection of wild fish by commercial merchants in New Guinea, although reliable data is lacking.

In Australia, the relevant authorities of the States and Territories control the collection of rainbowfishes from the wild and permission will only be granted where the taking of the species from the wild is not detrimental to the survival of that species or its habitat. The export of rainbowfishes from Australia is also controlled by the Wildlife Protection (Regulation of Exports and Imports) Act 1982. This Act regulates the importation and exportation of most live animals and plants. Approvals to export live rainbowfishes may be given where the fish have been bred in captivity or taken under an approved collecting permit.

Rainbowfishes form the most speciose group of fishes inhabiting freshwaters within the Australia-New Guinea region. Despite this, relatively little is known about rainbowfish biology or ecology in their natural habitat. Most information is mainly based on aquarium observations.

In their natural environment rainbowfishes are generally aseasonal breeders, spawning opportunistically at intervals over a period of about four to five months of the year. Most however, show a peak in reproductive development during the early-wet season. Rainbowfishes usually move out of their dry season habitats to take advantage of the extensive flooding, which often causes an increase in plankton and other foods. Flooding also increases the area and diversity of aquatic habitats available. The young are spawned when food is plentiful and when aquatic plant communities are most dense, affording them protection from predation.

Spawning activity normally peaks during the wet season (November to May) in floodplain rivers, but can also occur in streams during the dry season (August to November). Although, spawning will vary from region to region and in some cases from headwaters to lowland reaches when flow rates are reduced and the occurrence of a water flow resulting from sudden rain is significantly reduced. However, rainbowfishes will normally breed when environmental conditions ensure maximum larval survival.

The precise regulatory role of environmental factors on the reproductive cycles of rainbowfishes is not known. Spawning is regulated by external environmental factors that trigger internal biological functions. The internal biological functions that regulate spawning are similar for most fishes. External environmental factors that control spawning, however, vary considerably. Environmental factors that have been shown to play a significant role in the reproduction cycle of rainbowfishes are: photoperiod; water temperature; water quality; flooding and water flow; rainfall and availability of food. These factors do not function independently of each other, but are interrelated. Actual spawning occurs in response to short-term stimuli such as colouration or pheromones of a mate. Pheromones are chemical messengers like hormones but instead of carrying information within an individual they carry information between individuals of the same species.

Male rainbowfishes can be highly territorial and will engage in the acquisition and defence of spawning sites (submerged logs, rocks, vegetation). Females move between territories, inspecting males along the way. Males play an active role in courting females and will often swim over to display to passing females. If successful in his efforts, the female will follow the male to his territory and scatter her eggs among aquatic vegetation. After spawning, the female will leave, while the male remains displaying to passing females and thus defending his territory and the fertilised eggs.

Rainbowfishes generally spawn small numbers of eggs over a large area in slow-flowing waters and the backwaters of floodplain areas. This strategy increases the chances of some eggs surviving. The presence of extensive spawning substrate enables them to 'spread the risk' from predators. The eggs are attached by adhesive threads or tendrils to a range of submerged physical structures, including gravel substrates, woody debris, root masses, aquatic vegetation and submerged marginal (riparian) vegetation, which hide them from predators. However, the eggs are subject to desiccation if the water level drops or to dispersal if there is a flood.

Fortunately, rainbowfishes in captivity are very adaptive and will breed under a variety of conditions, and are in the main, influenced by photoperiod and temperature. Subtle changes in water chemistry will also have some influence on the spawning of rainbowfishes. Therefore, maintaining them in an appropriate captive environment will ensure successful breeding. First, you do not breed your fish; they breed themselves. What you have to do is provide them with suitable conditions and they will do the rest. Successful breeding will depend on a number of things such as nutrition, temperature, the number of fish in the aquarium, the age of the fish, and sex ratio.

In addition to the regular aquarium, breeding usually requires one or more separate aquariums for conditioning the breeders, spawning, and rearing the juveniles. Before attempting to breed your rainbowfishes, you should feed them with the best food you have available for at least two preceding weeks. Most species will breed successfully when fed commercially manufactured fish food (43% protein; 12% lipid), but feeding with live and high-protein frozen foods will maximise egg numbers. Feed at least every day making sure you don't overfeed. To increase your success, and prevent uncontrolled spawning, try separating the males from the females during this two-week period. Separation of the sexes elicits a synchronisation of spawning that result in a larger number of eggs.

Rainbowfishes are sexual dimorphic and can be sexed by their colour and finnage. Males are generally very colourful, have extended finnage, while females are pale by comparison, and have smaller or more rounded appearance in the fins. Generally, the larger males can usually be identified from the elongation of posterior rays in the second dorsal and anal fins. In addition, males generally are larger and have a deeper body than females. These physical differences make it relatively easy to identify mature males. However, female characteristics such as plumpness of the abdomen are subjective and can be misleading. If you are unable to sex your fish, then have someone with more experience do it for you.

By far the best combination for breeding is 3 males and 2 or more females. With 2 males one will dominate the other and in effect prevent him from breeding. While a single male may cause undue pressure on the female/s. Three on the other hand will keep inter-male aggression within bounds and spares the females physical abuse. In a large aquarium, it is possible for males to have their own spawning space. This will allow the females to choose their own mate and in doing so; a variety of genes will be passed on to the next generation. In addition, this method should provide you with more eggs.

Pair breeding is also an acceptable way for obtaining eggs. This method is especially well suited for selecting individual fish for genetic reasons. However, group spawning is the method of choice because it produces less stress on the fish. Females spawn a limited number of eggs at a time, and on average, 60~80% of females set up for group spawning will produce eggs. Group spawning with multiple males and females is more natural. In the wild, a female has the choice of either spawning or fleeing. In captivity, the flight of the female is reduced or confined to the size of the breeding aquarium. Therefore, the size of the breeding aquarium is vitally important and should be appropriate for the species being bred. Breeding aquaria should not be less than 55-L in size, and are probably best left completely bare with a small internal sponge or box filter. Water temperature can be maintained at around 28°C (± 2°C). A photoperiod of 16 hours light: 8 hours of darkness usually gives the best result. Water chemistry is not a major factor providing it falls within that shown in the following water chemistry table.

Choose your breeders and place them in the breeding aquarium. Spawning activity should commence within 24 to 48 hours. Spawning behaviour typically begins half an hour after the lights are turned on in the aquarium, with a peak of activity around 1~2 hours later. Activity then gradually declines until all spawning activity has finished, usually by mid afternoon.

Males display to each other by extending their dorsal and anal fins, while at the same time intensifying their colouration [M. trifasciata] - photo© Gunther Schmida

Males display to each other by extending their dorsal and anal fins, while at the same time intensifying their colouration. The extension of the fins is an illusionary aspiration by the males to increase their overall body size as they complete with each other for the attention of a female. This is often accompanied by a side-slapping action while swimming together side by side throughout the aquarium. Extended fin and colour intensity is also undertaken by the male when displaying to a female, only this time it is an attempt to increase their overall attractiveness to the females.

During pre-spawning activity, males can become quite aggressive and actively pursue the females. Actual spawning is preceded by vigorous coercing by the male. The male swims around the female with all his fins expanded, making repeated sideways motions or "nods" in the direction of the female, while at the same time intensifying his colouration. During this procedure the colours in both sexes become more intense, but to a lesser extent in the female. Males frequently "flash" an instantaneous brightly coloured band that runs from the upper lip to the first dorsal fin, which they flash on and off like a neon sign. The colours range from white to yellow, orange, rustic red and light blue, depending on the species.

Males frequently flash an instantaneous brightly coloured band that runs from the upper lip to the first dorsal fin, which they flash on and off like a neon sign [M. maccullochi] - photo© Neil Armstrong

When receptive, the female will enter the spawning site first, closely followed by the male. In the final phase of spawning, the male presses against the side of the female and, accompanied by much trembling action from both fishes, eggs are expelled directly among the plants or spawning medium. Spawned eggs are adhesive, negatively buoyant in freshwater and average 1.5 ± 0.5 mm in diameter, are usually clear to light amber in colour and hang by a fine thread. Usually one to three eggs are deposited at a time, during which time 50~100 eggs can be produced. In captivity, however, with limited area and artificial substrate, females may spawn all their eggs at the same time. The number of eggs shed by a single female is directly related to the size of the female with large females spawning from 40 to 250 eggs, with a fertilisation success rate generally around 70~80%. The total number of eggs released will increase with the maturity and size of the fish. Females usually only spawn once each day; however, males will often spawn with more than one female in one day. The eggs hatch into well-developed larvae after an incubation period of around seven days. They are good swimmers, efficient feeders and fast growers; maturing within one year.

Despite what you may hear or read most rainbowfish will eat their eggs, maybe not all of them, but they will certainly eat what they can find and I have never seen a rainbowfish that doesn't eat fish eggs. The breeding male will attempt to keep all the other fish away from his spawning site and eggs, but by and large it doesn't work too well. To insure maximum egg survival, check the spawning mops regularly.

If you have a continuing problem with egg eating, you might like to use a stiff bottle brush as a spawning medium. Commercial breeders use these to spawn tropical fishes that regularly eat their eggs. The stiff bristles function as a medium in which the adhesive eggs can be laid, while at the same time, discourages the breeders from eating the spawned eggs. Feeding live foods can also reduce any egg-eating behaviour. A notorious egg-eater often encountered when breeding rainbowfish is a little freshwater flatworm called planaria. If you get them in a breeding aquarium, they can consume a whole spawning of eggs within hours.

Java moss or any similar 'aquatic moss' is a suitable live plant for breeding rainbowfishes and grows well under the low light conditions of most breeding set-ups. Even so, spawning mops are my preferred spawning medium. Spawning mops can consist of bundles of fibrous material arranged in a variety of forms and made from a variety of different materials. However, one of the easiest methods is to use acrylic thread (about 8 ply), boiled to remove excess dye, cut to the desire length and tied together in the middle. For a more natural appearance, you could use green coloured thread to simulate aquatic vegetation. Typically, spawning mops are suspended in the water column or laid along the bottom or sides of the breeding aquarium. The mops can be attached to a block of styrene foam and floated in the water. You can provide several mops to offer the males a choice of spawning sites and females a choice of hiding places. Egg-filled mops are removed from the spawning aquarium and placed in another aquarium for incubation and larval rearing.

Before being used for different rainbowfish species, mops should always be boiled or sterilised to destroy any eggs or pests, which may still be attached to the mops. This procedure effectively precludes inadvertent hybridisation resulting from accidental carryover of eggs from the breeding aquarium of one species to another, and demonstrates a significant advantage that artificial spawning medium has over live plants.

© Copyright Adrian R. Tappin
Updated December, 2008.