Livebearers belong to the massive order, Cyprindontiformes and are made up of, among others, the families Anablepidae, Goodeidae, Hemirhamphidae, and Poeciliidae. Livebearers are the most popular of all aquarium species due to the wide availability, relatively peaceful behavior, and their colors. Livebearers have a wide range of appearance, from the common guppy to the odd Freshwater Sting Ray (Potamotrygon sp.). Livebearers are distributed throughout Southeast Asia, the Americas, and the Caribbean.
The eggs are fertilized internally in the female. The eggs are fertilized by the male through a mating organ, usually a modified anal fin. The embryos develop in one of two ways depending on the fish: (1) In ovovivoparous species, the young develop inside eggs within the mother's body. The nourishment is provided by the yolk of the egg. The young hatch inside the mother's body and pass out through the anus. (2) In viviparous species, the young develop without egg inside of the mother's body. The young are nourished by secretions of the female or through an umbilical-like cord.