Mollies are easy-to-keep tropical fish ideal for novice aquarists. Mollies, of family Poeciliidae, come in colors including black, white, orange, marbled and others. Mollies can be fun to breed. Differing between the male and female members of the species is easy to do.
It is fairly easy to determine the sex of a male molly. Males are more torpedo-shaped and have bigger fins than females. The males also have pointed gonopodia, modified anal fins they use to mate with females. Dominant male mollies intensify in color and grow larger fins to produce a mating show for females or to show dominance to other males.
Female mollies have bulky figures; they're wider than males at the rear of the abdomen for breeding purposes. When pregnant, she will take on a bulging, lumpy appearance. Her fins are shorter; the anal fins are triangular.