A variety of fish that bears live young. The eggs are fertilized within the body of the mother and develop there, as opposed to egg-layers, whose eggs are fertilized after being laid. The most well known family of livebearers is Poeciliidae, also known as the livebearing toothcarp. Examples include the guppy, molly, platy, swordtail, and gambusia. Synonym: viviparous.