The male molly is more slender and has a gonopodium, a modified anal fin functioning as a reproductive organ, while the female is longer and rounder in size. The female Poecilia sphenops, commonly known as a molly, is generally about 4.8 inches and the male is 3.2 inches in length.
Molly fish are live-bearing and thrive with multiple females and one dominant male in a tank. Male mollies can be moderately aggressive, which can cause stress in tanks with multiple males. Molly fish are highly adaptable to either fresh or saltwater tanks and have a high birth rate. A separate breeding tank is recommended, and the female should be removed after giving birth to prevent the female from eating the fry.