Poeciliidae

Poeciliidae are a family of freshwater ray-finned fishes of the order Cyprinodontiformes, the tooth-carps, and include well-known live-bearing aquarium fish, such as the guppy, molly, platy, and swordtail. The original distribution of the family was the Southeastern United States to north of Río de la Plata, Argentina. Due to release of aquarium specimens and the widespread use of species of the genera Poecilia and Gambusia for mosquito control, though, introduced poeciliids can today be found in all tropical and subtropical areas of the world. In addition, Poecilia and Gambusia specimens have been identified in hot springs pools as far north as Banff, Alberta.

== Live-bearing == All species in the Poecilidae are live-bearers. Differences are seen in the mode and degree of support the female gives the developing larvae. Many members of the family Poeciliidae are considered to be lecithotrophic (the mother provisions the oocyte with all the resources it needs prior to fertilization, so the egg is independent of the mother), but others are matrotrophic (literally "mother feeding": the mother provides the majority of resources to the developing offspring after fertilization). Lecithotrophy and matrotrophy are not discrete traits. Most scientific studies quantify matrotrophy using a matrotrophy index (MI), which is the dry mass of fully developed offspring divided by the dry mass of a fertilized egg.