All of the members of the subfamily Poeciliinae are ovoviviparous, i.e. they give birth to live young, except Tomereus, with internal fertilisation and a large yolk in the egg.

[2] The Poeciliinae are predominantly freshwater fish but some species live in brackish water, and some can even tolerate seawater.

Some of the world's most popular aquarium fish such as guppies, swordtails and mollies are from this subfamily.

[2] They have been introduced to many regions in the world, either accidentally or to control mosquitoes, and have become invasive species threatening local populations of similar, small fishes.

[3] For example, the Eastern mosquitofish Gambusia holbrooki is considered to be one of the 100 worst invasive species in the world and is responsible for declines in small native aquatic species worldwide.