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female guppy livebearer
Female Guppy, photo: CC Wolfgang

Breeding Aquarium Fishes, Part 1 Livebearers


Some of the more popular Livebearers which we are all very familiar with and which most of us kept in our first community aquarium are without doubt the easiest of fishes to breed in captivity. Many of the people reading this will have switched the light of their aquarium on in the morning and found a brood of tiny fish which were then placed in a breeding net and hung on the side of the tank where the fry grew ever so slowly and really didn’t do all that well and proved to be worthless when it came to trying to sell a few.
This scenario takes place with monotonous regularity and it is such a shame because with just a few small changes it is possible to raise a full brood of healthy little fish which would be easy to sell or exchange for some fish food at your local aquatic pet store.


female guppy livebearer

Female Guppy, photo: CC Wolfgang

How to do it properly

Selecting the parents: Using guppies for this example. First it is important to select some good parents. These are best obtained from a breeder who has a good healthy recognised strain and where the sexes are kept apart so that the female guppy isn’t already pregnant. This is important because female guppies can store sperm and they will produce several broods from a single mating. Any adult female which has been kept with males will be pregnant and we will have no idea about the quality of the father. Select fish which are quite young about 3 – 4 months old if possible which is the stage where the fish should look almost adult but not quite at their peak for size and colour. They should be free from deformities and have a good deportment. Avoid males where their tails look to heavy when they swim or fish with bent spines as this indicates to much inbreeding.

Pre-breeding care: Set up an aquarium of about 100 litres using just a very thin layer of substrate for ease of cleaning, a mature air operated sponge filter and lots of floating plants such as Indian fern, Ceratopteris thalictroides which will quickly cover the surface and send down lots of trailing roots which offer a great habitat for very small guppies. Keeping the sexes apart keep them in slightly alkaline water with a pH of 7.4, but remember guppies are very adaptable fish and a pH anywhere between 6.5 to 7,8 is acceptable.  the temperature should be slightly higher than it would be for normal maintenance and should be set around 24 – 26°C.
For the next 3 or 4 days feed the fish with a high protein diet of live or frozen food such as daphnia, cyclops, brine shrimps, and similar. On the fifth day place the fish (1m and 2f) in the breeding aquarium and leave them to it. They will begin mating almost immediately but due to the size of the tank and floating plants the male won’t harass  either female to much.

Breeding: Being live-bearers the females eggs are retained within the mothers body and so they have to be fertilised inside her, for this to happen the male has a specially modified anal fin which acts like a sex organ in mammals. The anal fins of all male live-bearers are modified in this way and because of this modification they are called “gonopodium” rather than anal fin. The gonopodium makes it very easy to sex live-bearers because the anal fin of the female is unmodified.

Guppies don’t require any particular triggers to initiate mating, simply keeping the two sexes of healthy individuals in the same aquarium is all that is required. The male will be seen approaching the female with his fins held erect and quivering, which is his way of showing what a good male he is. The female appears to ignore his advances but he will persist even chasing her if necessary. When he manages to get in to position the actual act of mating is often over with faster than you can see it but it will occur many times per day.

After a week or so the male can be removed from the breeding tank and the females will then be left in peace, by this time the likelihood is that both will pregnant. If the females are fed extensively with live food such as daphnia to the point where they begin to lose interest in it and ignore live daphnia in their tank they will be far less likely to eat their own fry (young fish).

The birth and raising the fry

Guppies are born at a much later stage than most other fish. When egg layers hatch they still have a large yolk sac attached and are unable to swim, they remain like that for about a week after hatching and then once the yolk sac is used up they will begin free swimming and looking for food. Guppies remain inside the female for the early stages and when they are eventually born they are quite large and well developed compared to the fry of most egg layers. As the female gets closer to giving birth she will become much fatter and a dark spot (gravid spot) above her anal fin will darken. When the fry are born they may still be in a membrane which will break open almost immediately and the newly born fry will rest on the bottom of the tank for a short time. After a minute or so the fry will swim up towards the light and take refuge among the hanging roots of the Indian fern (any fine leaved plant will do if it is allowed to float if you can’t get Indian fern) and once there the fry will be relatively safe. Once both females have finished giving birth they will show no further interest in their fry except perhaps as food. At this stage for the fry’s safety the females should be removed too and the fry left in the tank on their own.

The care that the fry receive in these early days will have an influence on how they grow up. The two main influences are food and water quality and both are of equal importance. The fry will accept finely crushed flake food right from day one but using this alone isn’t the best option because very young rapidly growing fry need lots of protein or their growth will be stunted. Newly hatched brine shrimps, micro worms, hard boiled egg yolk (in very small amounts smeared on the inside of the glass are all very good for providing extra protein and they should be used to supplement the flake food. The flake food is important too because it has added vitamins and important minerals and will help to provide a complete diet.

When carrying out tank maintenance such as water changes, filter cleaning and substrate cleaning don’t be to pedantic about making the sponge filter spotless. A sponge filter will trap small fragments of food and it will quickly develop a bio-film on its surface where all manner of small microscopic organisms will be in abundance. The fry will often be seen grazing on the surface of the filter and it is a great source of food for them, don’t waste it by trying to be too clean.

Water changes are absolutely vital too. The usual 25% per week is far to little for growing fry, a far better option is 20% daily to begin with increasing to 35% daily when the fry are larger, this might seem excessive but it will along with a good diet help to achieve maximum growth of the fry with no stunting at all. A good sign that all is going well is even growth of the brood. Obviously the females will grow faster than the males because they end up being much larger fish, but all the females should be of a fairly even size and all the males should be of an even size. A brood where there is a great variation in size has gone wrong somewhere and it is one of the tell tale signs a dealer will look for when assessing the brood for purchase.

If everything has been done correctly the fry should be near adult size in just ten weeks

What not to do

Like all fish and despite their great adaptability and general hardiness guppies can feel stress this should be avoided at all costs where possible or it may impact on the health of the fish, this is particularly true when dealing with pregnant live bearers.

  • Never try to catch a heavily pregnant live bearer because it may induce a premature birth and it can also damage the mother.
  • Don’t place a heavily pregnant live bearer in a breeding net inside a community aquarium. Every instinct of a live bearer which is close to giving birth is telling it to find a very secluded spot and hide in order to protect her new fry when they are born. If she is placed in an open net near the surface right under the bright lighting and on full view she will find the experience extremely stressful and again this could induce a premature birth or the complete opposite and cause the female to resist giving birth which will eventually result in the fry being born dead and possibly cause the premature death of the mother.
  • Don’t try to raise a brood of fry in a breeding net in a community aquarium. They can’t be properly fed in such a situation and water changes which are deemed adequate for a community tank will be far to small for growing fry, the result will be permanently stunted fry which never achieve their full potential.
  • Don’t try to use a power filter with small fry, they will end up inside it dead. Don’t listen to those who (with good intention) suggest placing some old tights over the strainer to prevent the fry from being sucked in, all this will achieve is to get the fry stuck to the surface of the tights and unable to get away due to the powerful suction of the filter. The only safe filter is an air operated sponge filter where fry are concerned.
  • Don’t try to raise too many fry. Even with this regime overcrowding will result in some stunting of growth. Also there is a limit to what a dealer will want to buy and if you saturate an area with the same fish which the dealer is then stuck with it won’t endear you to him and he’ll remember for next time too. A 100 litre tank will be good for raising about 30 fry under this regime but they will be thirty good fry and this is far better than trying to raise 100 sickly runts which will never make good fish.
  • Don’t expect to make a fortune out of breeding your fish because you won’t in most cases you will be lucky to get back the money you have spent on them. Breeding fish is interesting and extremely rewarding and those are the real reasons for doing it.


Of course you don’t have to go to the trouble of getting your stock from a specialist breeder and if you are one of the many who everyday find some guppy fry in their community aquarium the advice on raising the fry can still be followed and it will reward you with far better results than any breeding net will.
Platies and Swordtails can be bred in a very similar  way using this method but Mollies are far more delicate and need particular attention paying to their care. More difficult species like Pike live bearers, Belonesox belizanus and Malayan  halfbeaks, Dermogenys pusilla will be dealt with in future articles.

About Andy Rapson

I've been interested in fish for about fifty years and I have kept many different species in that time. I have also worked in the fish trade running my own fish shop and I'm a Fishbase collaborator. I'm now mainly interested in fish husbandry, fish health, native marines and fish photography.

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