Poecilia sphenops is a species of fish, of the genus Poecilia, known under the common name molly; to distinguish it from its congeners, it is sometimes called common molly. They inhabit fresh water streams and coastal brackish and marine waters of Mexico. The wild-type fish are a dull silvery color, often sprinkled black all over. The molly can produce fertile hybrids with many Poecilia species, most importantly the sailfin molly. The male black mollies generally tend to be mildly aggressive.
Mollies rank as one of the most popular feeder fish due to high growth rate, birth size, reproduction, and brood number.
Contrary to popular belief, this species of fish is actually a freshwater species, spending little time in brackish water before swimming back to their freshwater biotope. However, fish of the same species have been found in coastal sea waters, brackish swamps and freshwater streams, living, and breeding. Mollies appear to be a hardy and highly adaptable species (this has been diluted over years of interbreeding in tank-bred specimens).
Mollies are similar in appearance to their livebearer cousins, the platy, and swordtail, although the molly tends to be slightly larger and more energetic. Many aquarists note the stronger individuality and aggression in keeping mollies versus platies, who appear much more docile.
Selective breeding over centuries has produced several color variations and different body shapes. The wild-type fish are a dull silvery color, often sprinkled black all over. The molly can produce fertile hybrids with many Poecilia species, most importantly the sailfin molly. The wild form is in fact quite rarely kept, as it has a rather plain silvery coloration suffused with brown and green hues.
Black molly - It is a melanistic breed which is black all over.
White molly - It is a leucistic breed which is black all over.
Yellow molly
Red molly
Balloon molly - This fish has a deformed spine due to a genetic defect that gives it its appearance. Through selective breeding it is now widely available. Balloon mollies can still reproduce and live a normal life comparable to that of other mollies, but it has garnered controversy due to the belief that its defect gives it a shortened lifespan and a susceptibility to health problems.
Lyre-tail - A breed with an altered caudal fin structure.
A female spotted molly fish, ~4 years old.Black-and-white molly - A white-colored breed with black speckles.
