The Sailfin Molly, Poecilia latipinna, is a species of fish, of the genus Poecilia. They inhabit freshwater, brackish, and coastal waters from North Carolina to Texas and the Yucatan Penninsula of Mexico.The sailfin molly was originally described in 1821 as Mollienesia latipinna by the naturalist Charles Alexandre Lesueuer, who based his description upon specimens from freshwater ponds in the vicinity of New Orleans, Louisiana. Sailfin mollies feed primarily upon algae and other plant materials, although they will consume a number of aquatic invertebrates, including the larvae of mosquitos. The sailfin molly is a tolerantt species, as it can exploit the thin film of oxygen-rich surface water with its upturned mouth, so is able to survive oxygen-depleted habitats. A euryhaline species, the sailfin molly may be found in a variety of saline environments, tolerating salinities as high as 87 ppt and breeding in brackish waters.

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.

The Blackfin shark will do well in any freshwater aquarium with some salt added, or in a Brackish water aquarium.