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 red-tailed black shark (Epalzeorhynchos bicolor; syn. Labeo bicolor), also known as the redtail shark and redtail sharkminnow, is a species of freshwater fish in the carp family, Cyprinidae. It is endemic to Thailand and currently critically endangered, but common in aquaria, where it is prized for its deep black body and vivid red or orange tail. The red-tailed black sharks seen in the aquarium trade today are all captive bred. It is not closely related to sharks.