Rainbowfish breeding and spawning

Rainbowfish sexing

Most rainbows can be sexed fairly easy since the males tend to develop more vibrant colours and longer dorsal and anal fins. If you keep species such as Boeseman's rainbowfish (Melanotaenia boesemani) or Banded rainbowfish (Melanotaenia trifasciata), sexing will be somewhat trickier, especially in younger specimens. Even in these species, there is however normally a difference in length when it comes to the first dorsal fin. If the first dorsal fin reaches the beginning of the second dorsal fin or proceeds even longer, you are most likely looking at a male rainbowfish.

Breeding rainbowfish

If you wish to breed rainbowfish, you must of course start by having at least one specimen of each sex in the aquarium. This part is not very tricky, since rainbowfish is fairly easy to sex. Some species spawn in pairs while others spawn in groups. It is always advisable to obtain species specific information before you attempt to breed rainbowfish. By doing so, you will learn more about the breeding behaviour of your particular species and how to increase the chance of successful breeding in the aquarium. Species that spawn in groups should normally be kept in groups consisting of 2-3 females for each male.

Breeding aquarium

If you want to, you can set up a separate breeding aquarium for your fish. A breeding aquarium doesn’t have to be as big as a normal aquarium. A majority of the rainbowfish species will breed in aquariums no larger than 40-50 litres (11-14 gallons). Cover the bottom with a thin layer of gravel and include java moss or spawning mops to act as spawning sites. If you use mops, make sure that they almost reach the bottom of the aquarium since many species of rainbowfish are accustomed to spawning roughly one decimetre (4 inches) above the bottom. Aeration is mandatory, but a lack of filtration can be remedied by small and frequent water changes.

Courting and spawning

Rainbowfish normally spawn during early morning. The male will pick out a spawning place in the aquarium and court the female by swimming rapidly back and forth in front of the spot to attract her. He will keep his dorsal and anal fins fully erect to look as strong and dazzling as possible. It is common for courting males to display an intensely dark fin margins, and many species will also be decorated with a neon stripe on the forehead. The female can watch him swim back and forth for several minutes before she decides if she wants to go to the spawning place. Sometimes the male can be seen nudging the female near her pelvic base now and then for a period of up to five minutes, before the actually spawning starts. During spawning, the two fishes will take up position next to each other with their heads pointing in the same direction. While the eggs are released, both fishes will tremble forcefully. Healthy and well-fed rainbowfishes are capable of laying eggs almost everyday during the breeding period.

Eggs

The number of eggs varies; sometimes a female will release less than five eggs and sometimes a batch turns out to contain over 30 eggs. The eggs are adhesive and will stick to the java moss or mop. Each egg is around 2 mm long and clear.

Since rainbowfish are known to eat their own eggs, it is safest to move the eggs to a separate fry rearing container. A 2-litre plastic container from the kitchen is large enough to work as fry aquarium for 25 fry while the fry are still young. Use water from the breeding aquarium to fill them, that why the eggs does not have to adapt to new conditions. Make sure that the temperature is kept up in the fry aquarium. One way of achieving this is to let the containers float in another aquarium or in a tub where you have placed an aquarium heater or two. The temperature should be kept in the 25-28 degrees C (77-83 degrees F) range.  

You should ideally check the breeding aquarium for new eggs several times each day; otherwise the parents might eat the eggs before you notice them. Take the java moss or mop out of the water and squeeze out the water before you start removing the eggs. When you find a strand where eggs have been attached, you simply break or cut it loose and put it in the fry rearing container. How long you have to wait for the eggs to hatch varies greatly between the species. Some species have eggs that hatch within a week, while others need several weeks to develop even when the temperature is kept within the recommended range.  

Fry

When the fry hatches they will be roughly 4 mm (1/6 inch) long. They fall down to the bottom as they hatches and stay there for a day or two, before they swim up to the surface. The aeration should be kept gentle once the eggs have hatched.  When the fry have consumed their yolk sacs you can start feeding them infusoria or liquid fry food. As the fry grow bigger, you can give them newly hatched brine shrimp and microworms. It is important to keep the water quality up in the fry rearing container. Remove all uneaten food after each feeding and carry out small and frequent water changes. Large water changes can shock the fry.

Hybrids and geographical varieties

If you keep more than one species of rainbow fish in your aquarium it can result in hybrids. Unlike many other animals, rainbow fish can quite easily breed with each other even if they belong to different genera. Even in the wild, hybrids between New Guinea rainbowfish (Melanotaenia affinis)andHighlands rainbowfish (Chilatherina campsi) have been found. Hybrids are a problem for the hobby since it makes it difficult to tell which species you actually keep and what its genetic heritage and requirements are. Hybrids should therefore not be sold or given away, since that means giving up control over the hybrid. There is no way for you to know what will happen to that hybrid; it might end up in the hands of a dishonest or simply uninformed person that will try to pass it of as a true species or even sell it as a “new” species. If you want to keep several species of rainbowfish together, the safest course of action is to let the fry become live food for adult fish or keep them to yourself for the rest of their life. 

When breeding Rainbowfish, it is also of interest to separate the various geographical varieties from each other to preserve their uniqueness. If you know that your rainbowfish have been wild caught in a certain location or are 100% sure that they hail from such ancestors, it is advisable to breed them only with other rainbows from that exact location. Rainbowfish are assigned geographical codes which are used to separate the various populations from each other. Melanotaenia trifasciata (commonly known as the Branded Rainbowfish) is for instance known as Melanotaenia trifasciata - Archer River, Melanotaenia trifasciata - Giddy River, Melanotaenia trifasciata - Goyder River, Melanotaenia trifasciata - Running Creek, and so on depending on geographical location.

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