How to breed livebearing fish

e3698611-f7f4-45d5-99b3-9eb5519b6e78

Editor's Picks
Sometimes pricy, sometimes cheap. Credit: Shutterstock
Features Post
Are fish really worth the price?
07 November 2019
Readers Tanks Post
Your tanks: Mark Allison
30 October 2019

Just started keeping fish? Fancy breeding some? Jeremy Gay introduces you to some tropicals which take zero encouragement to get frisky!

You've just set up for tropical fish and your tank is either cycling or just cycled. First fish would have typically been half a dozen Zebra danios, all doing well, and soon your shop will allow you to stock a few of the species you really took up the hobby to keep - the colourful ones.

High on your list will be guppies, Siamese fighters, angels and Neon tetras. Why they aren't a good idea to keep together is the subject of another article, but if you do get your hands on some guppies, platies, mollies, Swordtails or Endler's, you will more than likely start to breed them.

Guppies and their relatives are known as livebearers or, more scientifically, ovoviviparous, meaning that the female fish is inseminated internally - like mammals - with the eggs developing and hatching internally. She then gives birth to live young, which fend for themselves as soon as they are born.

This is a survival strategy as, being small fish, livebearers are low down in the food chain and heavily predated in the wild.

By popping out live young, parents don't need to expend time and energy protecting eggs and the sooner the fry become sexually mature, the sooner they can procreate to ensure the species survives if the parents get eaten.

Given that the guppy is one of the most prolific fish on the planet and has earned the name of 'millions fish‚' it's a survival tactic that definitely works.

How to sex livebearers

There are several ways to determine male from female, but these are the three most straightforward methods:

Check the fins

The organ the male livebearer uses to inseminate the female is called the gonopodium. It's a modified anal fin and quite visible under the belly, looking like a spiky fin instead of the average triangular-shaped anal fin of the females.

This averages about 10mm/0.4" and the males can move it around, especially when females are close.

Male livebearers may also sport some attractant in the form of bright colours or modified tail or dorsal fins, which they use to display to females and coax them near enough to be inseminated.

With Swordtails, for example, only the male has the elongated swordtail, while a female's looks more like those of a platy. With Sailfin mollies the larger dorsal fin is the giveaway.

Compare size

Because females have to carry a belly full of large fry, they grow larger than males of the species. When full of fry, female bellies will also become very distended.

Males, on the other hand, go for the "live fast die young" approach to life, as those fin extentions and bright colours make them more visible to predators in the wild.

Their mission entails mating before they get eaten - so being small works just fine.

The gravid spot

This is the name of the black mark visible on the bellies of pregnant females. It's most visible on olive-coloured, wild-type fish, though it may even show on bright red or orange ones too.

Only females have the gravid spot and it becomes most visible late in the pregnancy when large with growing eggs and fry.

Selecting parent stock

If buying your platies from a tank of both male and females it's highly likely that the females will already be pregnant. If they aren't, and you'll know over the next month of ownership, you are in a good position.

See stage one. If they do become more rounded within days or weeks of owning them and show signs such as the gravid spot, see stage two.

Stage one: Controlled breeding

Having virgin females is the best way to breed your livebearers, as this means you can determine which males they breed with. Tanks of males and females of the same colour variety are highly likely to be related and inbreeding is to be discouraged as it brings on genetic weaknesses such as deformities and disease.

If you want to line breed a variety for its bright red colour, for example, it's best to buy males and females from unrelated batches.

However, if you want to create your own variety, females of one colour could be mixed with males of another. This will also ensure unrelated parents are used.

To have full control you could even consider keeping males and females in separate tanks, with a third one used for mating one specific male to one specific female and for raising fry later on. Note that females can store sperm after mating, so if you mate her once she could produce three batches of fry from the same original mating.

Stage two: Happy accidents

This is often the most likely scenario - your female fish showing signs of already being pregnant just after you buy them. You then have to make a choice. You can leave them to get on with it, give birth and the fry may survive predation without help from you, or you can intervene using a number of methods and contraptions.

Go for it if you want to leave them to do their thing, but if, like most people, you find the idea of newborns being chased and eaten by other larger fish disturbing, you'll need to protect those fry, either with a breeding trap or separate breeding tank. See next page on preparations.

Invest and take these steps to ensure you are well set up for those happy events:

Breeding traps

These are plastic boxes, usually transparent, that go inside the main tank. They either float or clip onto the rim and may come with or without a plastic lid.

Their design is quite clever as you place the pregnant female alone inside the trap and, when she gives birth, the live young swim through a slotted divider. ThIs prevents her eating them.

She is then returned to the main tank, the divider is removed and the fry are then kept separate from the adult fish in the main tank.

Breeding traps have tiny slots in the sides, allowing water movement inside but offering no escape for the fry.

Some traps can be subdivided, allowing two or more females to give birth at the same time, and some modern designs may even include an air stone for greater water circulation.

Fry can be raised exclusively in breeding traps, though, being small, they may not grow as quickly as in a larger, separate aquarium.

All in all, traps are cheap and readily available.

Breeding nets

These are larger than traps and can make a good transition for raising fry after they have outgrown a trap - and if you don't have a spare tank. As the name confirms, they are simple plastic frames covered in netting, allowing water movement but keeping in the fry.  

Nets could also be used in emergencies to hold bullied fish and these too are very cheap.

Separate tanks (picture by Ude, Creative Commons)

The best option is a separate tank, though it's also the most expensive. As with the main tank, you'll need to include a filter and heater, and the tank will need to be matured and kept running, ready for your fish.

They are better than traps and nets because they are larger, and some people feel that holding female livebearers in traps can be stressful - or simply too small in the case of large, female mollies.

In the wild females will instinctively look for a quiet area in which to give birth, among plants or roots, so in a separate tank you can add lots of feathery-leaved plants. When ready she will give birth in them.

The plants also give fry cover and the female can then be rested via a divider or returned immediately to the main tank.

Within the British fish club scene you can even buy special tanks for breeding livebearers featuring a V-shaped glass divider. At the end of the V is a slot, allowing only the fry through. This again is better for large females who won't be able to fit into traps.

When filtering any fry tank use an air-powered sponge filter, as this gentle filtration won’t suck up or damage any tiny fish.

Correct diet (picture by Ude, creative Commons)

Once the fry are born they will be immediately ready to eat and the more you feed them the better they will grow - water quality permitting. Even fry of Endler's livebearers, some of the smallest, could take powdered flake straight away. However, there are special fry foods of the right size for tiny mouths and nutritionally engineered to encourage maximum growth potential.

Liquid foods include Interpet's Liquifry numbers 1, 2 and 3. Number one is a liquid food for the fry of egglayers and two is a liquid food for the larger fry of livebearers. Three is a powdered food and can be fed straight away or when the fry are larger.

Many manufacturers produce powdered fry foods, so choose a reputable brand, like some of those illustrated here, and feed them until the fry are large enough to take adult foods.

You could also use nature's fry foods - Daphnia, known as water fleas, and Artemia, known as brineshrimp.

Daphnia can be cultured outside in water butts in summertime, the baby Daphnia being fed to fry, and Artemia can be cultured in kits indoors. Baby brineshrimp is one of the best-known fry foods for nearly all fish, so feed a diet that has liquid, powdered and live foods.

Feed three times a day if you can, change water as often as daily if you can, and remove any uneaten food to avoid pollution. Spread fry out in as large a tank as possible for maximum growth potential.

Rehoming plan

What do you do once you have these fry? If you are line breeding save a few of the best and breed them. If you end up with hundreds of unwanted fry over the space of a year you will probably need to rehome them.

Grow these as large as you can, as if you give away small fry they are likely to be eaten in any tank into which they are introduced.

Ask your local shop if they will take some, though don't expect anything in exchange as they will be offered fry weekly by customers and may already be overrun.

Cashing in?

You bought your fish for say £2 each and have now bred say 200 of them. That doesn't mean you will be able to sell them for £400!

The reason is that the hobby is saturated with young and adult livebearers, meaning it is a buyer's market and most potential buyers will be doing you a favour by taking them off your hands.

In addition, if you didn't line breed and select for strength, size and colour your fry may not be as good as their parents.

There's also a thriving livebearer industry in tropical parts of the world, so many hundreds of varieties are constantly on offer to our shops - and  they are usually available at knockdown prices.

If you could offer a few hundred well coloured, identically patterned and similarly sized fish for a just few pence each, and on demand, your shop may listen and agree to a deal.

However, if your fish are a mish- mash of size and pattern and sporadically available, don't hold your breath...

How many fry should you get and how often?

When livebearers start to spawn, it helps to have an idea of just how often you'll be hearing the patter of tiny fins.

Typically for most species, you can expect young at monthly intervals, although the size and fecundity of the female can play a role in frequency, with larger mothers holding on to their fry for long periods of time, and producing bigger fish at much higher volumes than their younger siblings.

The most commonly bred livebearer, the Platy, can release young every thirty days, and at full potential can produce up to 90 young per brood.

That equates to 1080 fry per female per year - explaining how some keepers can be over-run with them.

Less bountiful are guppies, which generally produce up to 50 young per sitting, and have been known to produce as few as two - although it is almost exclusively very young females that have such tiny births.

With these colourful fish, you can expect these offspring at 28 day intervals.

Swordtails tend to have longer cycles, and although they can produce monthly, they have been known to extend to 40 day cycles between broods. Again, parent size plays a big role in numbers produced, but 20 for a young fish, and 80 fry for an established, mature female are commonplace.

Mollies are the fry farms of the livebearer family, producing between 15 and 160 fry per spawning. Unlike their smaller relatives, some mollies aren't even sexually mature until they reach 6.5cm, which is as large as some of the other livebearers reach in total.

They also have the longest cycles of all, taking up to 48 days to produce young in some cases, often dependent on temperature. But in optimal conditions, producing 160 young every 28 days; that means a successful molly breeder could be looking at a potential 2080 fry per female, per year!

Why not take out a subscription to Practical Fishkeeping magazine? See our latest subscription offer.

Don't forget that PFK is now available to download on the iPad.