Live-bearing aquarium fish – often simply called livebearers – are fish that retain their eggs inside their bodies and give birth to live, free-swimming young. Among aquarium fishes only one live-bearing family, the Poecliidae, is really well represented. This family includes Guppies, Swordtails and Platies, Gambusia and Mosquito Fish (Heterandria) and the less well known Limias.
Most of the Poeciliidae are ovoviviparous, that is, while the eggs are retained inside the body of the female for protection, the eggs are essentially independent of the mother and she does not provide them with any nutrients. In contrast, fish such as splitfins and halfbeaks are viviparous, with the eggs receiving food from the maternal blood supply through structures analogous to the placenta of placental mammals.
In the pages under our livebearer drop-down menu, we discuss the different species separately.
The benefit for a fish that reproduces by giving live birth instead of laying eggs is obvious: the offspring is well-developed and self-sufficient in their ability to feed and move away from danger, or threats. The new generation’s survival is therefore safer than it is for an egg, or vulnerable larvae that may easily become food for others. The equation is that of saving ‘expensive’ survival energy: The parents’ method of reproduction means that they can produce less young and still ensure the survival of their species, while they need expend no energy at all on the building and guarding of nests or providing food, defence and care for their offspring – instead applying that ‘saved’ energy to their own survival.
Because the newborn fish are large compared to the fry of oviparous fish, they are easier to feed than the fry of egg-laying species such as characins and cichlids. This makes them much easier to raise, and for this reason, aquarists often recommend them for beginners to fish breeding. In addition, being much larger makes them far less vulnerable to predation, and with sufficient cover, they can sometimes mature even in a community tank.