Livebearers are the freshwater tropical fish species that do not lay eggs, but rather, give birth to live, fully-formed free-swimming young. They include the guppies, swordtails, mollies and platys. Breeding livebearers is one of the easiest and most exciting experiences in fishkeeping and here are a few tips on how to breed livebearers of your own.
Populate the tank with more females than males, preferably two females to every male. Adult male livebearers have a tendency to constantly follow and attempt to fertilize the females. Having fewer males will minimize the harassment and stress that the females could experience.
Take note of the females' maturity. Most female livebearers mature in about four months, which means that four months after birth, they are ready to become pregnant.
Remember that the average gestation period among livebearers is four weeks, therefore, once an adult female is fertilized, the babies are expected in about a month.
Note that female livebearers are capable of storing sperm in their bodies, which means that one fertilization session can result in several broods of fry.
Maintain several aquarium plants in the tank, preferably fine-leafed and reaching all the way up to the surface, to provide hiding places for young fry. If natural plants are not an option, artificial ones will serve the purpose.
When feeding the community tank, be sure to include fine flakes or fry food for the newborn fishes.
When a pregnant female becomes distressed before or after delivering her brood, consider segregating her from the community by transferring her to a hospital tank.
Prepare the breeding aquarium. Ensure optimum water conditions. Install the breeding net or breeding trap; these are usually available at the local pet store.
When the female looks about ready to drop her brood, gently transfer her to the breeding tank. Keep her over the breeding net or inside the breeding trap so that the young will be separated from her as they swim away. This will ensure that the mother does not eat her young.
Transfer the mother back to the community tank after delivery, which usually takes only a few hours.
Remove the breeding net or trap and maintain the breeding aquarium as a nursery tank until the fry are big enough to join the community tank.
The fry will be born with remnants of the yolk sac, which will sustain them until they are strong enough to feed. After a day or two, introduce fry food or very fine food flakes, making sure not to pollute the water with too much food.
Ensure ideal water conditions and regular feeding, and very soon the new brood will be ready to move to the adult community.
Livebearer males and females are easily distinguishable. Males are smaller and more colorful. Male guppies usually have long and fancy fins. Males have a gonopodium, which is a pointed extension on the underside, where females would have a fan-shaped fin. No special treatment is required when breeding in a community tank because, in effect, you are letting nature take its course. Pregnant females are ready to deliver their brood when they are round and fat, looking like they are about to explode. The underside of the stomach develops a dark spot called a "gravid spot" which looks like a window where you can almost see the developing young.
Because livebearers mature in four months and gestate in just one month, be prepared to deal with a growing population of several generations in a relatively short time. Be ready to lose several newborn fry because in a community tank, only the fittest and fastest ones will survive. The slow and weak ones will quickly become the adult fishes' next meal. Check your filter systems every now and then because tiny newborn fishes can sometimes get sucked into them. Some commercially available breeding traps are too small and tight for large livebearer females like the swordtails. Be sure to use a breeding trap that does not cramp or distress the pregnant mother. Consider using a breeding net or a converted aquarium.