- For the "Amazon river molly", see Poecilia amazonica.
The Amazon molly, Poecilia formosa, is a freshwater fish which reproduces through gynogenesis. This means although females must mate with a male, genetic material from the male is not incorporated into the already diploid egg cells the mother is carrying (except in extraordinary circumstances), resulting in clones of the mother being produced en masse. This characteristic has led to the Amazon molly becoming an all-female species. The common name acknowledges this trait as a reference to the Amazon warriors, a female-run society in Greek mythology. They are native to warm, fresh waters of northeastern Mexico and to the extreme southern parts of the U.S. state of Texas on the Rio Grande and the Nueces River.
In nature, the Amazon molly typically mates with a male from one of four different species, either P. latipinna, P. mexicana, P. latipunctata, or occasionally P. sphenops. One other male that could possibly exist in the Amazon molly's natural range that could induce parthenogenesis in Amazon molly females is the triploid Amazon molly males. These triploid males are very rare in nature and are not necessary in the reproduction of the species, which is why the species is considered to be all female.
The Amazon molly reaches sexual maturity one to six months after birth, and typically has a brood between 60 and 100 fry (young) being delivered every 30–40 days. This lends itself to a large potential for population growth as long as host males are present. The wide variability in maturity dates and brood sizes is a result of genetic heritage, varying temperatures, and food availability. They become sexually mature faster and produce larger broods in warm (approximately 80°F) water that provides an overabundance of food.
- NatureServe (2013). "Poecilia formosa". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 24 May 2014.
- "Poecilia formosa". Integrated Taxonomic Information System. Retrieved 6 June 2006.
- Froese, Rainer and Pauly, Daniel, eds. (2006). "Poecilia formosa" in FishBase. May 2006 version.
- Schlupp, I., R. Riesch & M. Tobler (2007): Quick guide –Amazon mollies. Current Biology 17: R536-R537.
- No sex for all-girl fish species BBC News, 23 April 2008
- Heubel, Katja U.: Population ecology and sexual preferences in the mating complex of the unisexual Amazon molly Poecilia formosa (Girard, 1859).Hamburg, University, Diss., 2004.