Poecilia sphenops is a species of fish, of the genus Poecilia, known under the common name Molly. They inhabit the coastal brackish and marine waters of Mexico. The wild-type fish are a dull silvery color, often sprinkled black all over.
This species is one of the ancestors of the black mollies, a number of melanistic breeds which are black all over. It is one of the most well-known aquarium fishes and nearly as easy to keep and prolific as guppies (for optimal health and breeding success, they demand fresh vegetable food like algae). There are several other popular breeds, like the golden molly nicknamed "24 karat", or the balloon molly, which however has a deformed spine and a decreased lifespan due to the associated health problems. Also, breeds with altered caudal fin structures like lyretails exist. The wild form is in fact quite rarely kept, as it has a rather plain silvery coloration suffused with brown and green hues. If given good care with ample sunlight, high water temperatures and fresh vegetables, they will, however, prove charming fish who make up for their somewhat plain coloration with their lively behavior.
The common molly can produce fertile hybrids with many Poecilia species, most importantly the sailfin molly. In the case of black hybrids, they are called midnight molly. These are very popular due to their impressive dorsal fins, but require a bit more attention and have a somewhat decreased lifespan - though certainly not as much as the deformed breeds.
Gallery of breeds
Female and (upper left) male silver molly
Artist's image of male double swordtail black molly. Note rather small dorsal fin.
Male gold mollies look very similar to some variable platyfish
Gravid female marble molly
Mollies are some of the easiest species to raise once you know what you are doing. They can be raised equally in fresh water, brackish, or fully saltwater. As a matter of fact, when I cycle a new saltwater tank, I alway use mollies...black, green, any color, it doesn't matter as the mollies swim bladder can easily adjust to the salt content as long as it stays on the lower level of seawater, like 1017-1022. No higher than 1022 is recommended, but can be done for short periods. The key to keeping mollies is that the tank needs to get an adequate amount of sunlight, so that natural algae can grow in the tank, which they will quickly devour like crazy. Only the green algae, not the hard or blue-green algae. Also, they need an abundance of live plants if possible, or vegetable flakes of some kind. They are omnivorous, but are mostly on the vegetarian side. The tanks need to be large and warm, no lower than 24°C or they will start to shimmy. At lower temperatures they will develop all kinds of illness: ich, velvet (most common) and flukes. 25-26°C is ideal.
Green mollies and short fin sphenops are extremely aggressive on females so you always need a 3 to 1 ratio otherwise the males will literally harrass them to death for sex. Lyretails are the most delicate and need to be kept away from aggressive fish that will nip their finds. Balloon mollies should never be overfed. After the first generation of mollies have bred, the young should be set up in their own tanks for full growth and maturation, otherwise they will quickly inbreed (amongst their siblings) and never grow to more than 5 cm. For proper growth, females should be keep separate from males for at least 6 months and fed on a varied diet. Store bought brine shrimp should never be feed to mollies, only home-grown. Best is frozen or freeze-dried to prevent parasites that come in off live shrimp. Keep the tank always on the hard water side and this will prevent skin infections. If you don't have live plants, crushed coral is the ideal bottom medium for mollies. Keep the tank swept or use fish that stir the bottom medium otherwise the rotting waste on the bottom of the substrate will cause the pH to turn acidic. Never overfeed your mollies, best to underfeed and let them forage for the rest of their meal thoughout the tank. I believe using this advice will give you as many wonderful years of pleasure that it has given me raising my mollies.
References
Template:Cyprinodontiformes-stub
de:Spitzmaulkärpfling fr:Molly (poisson) it:Poecilia sphenops nl:Black molly no:Molly pl:Molinezja ostrousta fi:Mustamolli sv:Black Molly (fisk) uk:Молінезія
