POECILIIDAE

'Poeciliidae' is a family of fresh-water fish which are live-bearing aquarium fish (they give birth to live young). They belong to the order Cyprinodontiformes and include well-known aquarium fish like the guppy, molly, platy, and swordtail. These fish originate from eastern United States to northeastern Argentina, Africa, and Madagascar.

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Live-bearing

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Live-bearing

Rather than describing the whole family Poeciliidae as "ovoviviparous", it is probably more accurate to say that the family consists of species which are all live-bearers, but that these vary in their reproductive life history: closely allied species within the same clade may show variable maternal provisioning. It is true that many members of the family Poeciliidae are considered to be lecitrophic (meaning that the mother provisions the oocyte with all the resources it needs ''prior'' to fertilization, so that the egg is independent of the mother), but others are matrotrophic (literally means "mother feeding": the mother provides the majority of resources to the developing offspring ''after'' fertilization).

Members of the genus ''Poeciliopsis'', for example, show variable reproductive life history adaptations. ''Poeciliopsis monacha'', ''P. lucida'', and ''P. prolifica'' form part of the same clade within the genus ''Poeciliopsis''. However, their modes of maternal provisioning vary greatly. ''P. monacha'' can be considered to be lecitrophic due to the fact that it does not really provide any resources for its offspring after fertilization - the pregnant female is basically a swimming egg sac. ''P. lucida'' shows an intermediate level of matrotrophy, meaning that to a certain extent the offspring's metabolism can actually affect the mother's metabolism, allowing for increased nutrient exchange. ''Poeciliopsis prolifica'' is considered to be highly matrotrophic, and almost all of the nutrients and materials needed for fetal development are supplied to the oocyte after it has been fertilized.
''Poeciliopsis elongata'', ''P. turneri'', and ''P. presidionis'' form another clade which could be considered an outgroup to the ''P. monacha''/''P.lucida''/''P.prolifica'' clade. These three species are very highly matrotrophic - so much so that in 1947 C. L. Turner described the follicular cells of ''P. turneri'' as "pseudo-placenta, pseudo-chorion, and pseudo-allantois".

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