According to Aquatic Community, mollies are highly recommended for beginning fish owners. These are relatively hardy and social fish, and are available in most pet and aquarium shops. They require only 10 to 20 gallons of water, depending on the type of molly, and feature several different colours and sizes. Most mollies go through similar lifespans, and can be long-lived fish under the right conditions.
Mollies fall into two different groups: short finned mollies, which include the popular black mollies and gold-dust mollies, and sailfin mollies, which are larger and more striking. Short finned mollies are more common in home aquariums, and are slightly easier to care for.
Mollies survive longest if they're kept in brackish (salt) water rather than fresh water, as it mimics their natural habitat more closely. The fish live for an average of three to five years, and become sexually mature when they're several months old.
Mollies are livebearing fish, which means that the males fertilise the eggs while they're in the female's abdomen, so the female can give live birth. This differs from most other fish, who lay eggs to reproduce. Female mollies may give birth to 20 to 40 babies at once.
Like many other fish, adult mollies have a habit of devouring their young. Any baby mollies must be pulled from the tank and protected until they're several weeks old, and large enough to fend for themselves in the main tank.
Aquatic Community states that mollies group together and form hierarchies when they reach breeding age. The large, most striking male molly becomes the alpha and surrounds himself with several females. Sexually mature males will fight to protect their territory and breeding females.
Mollies are social fish, and are best when kept in groups. They do well with other mollies, but can become aggressive and territorial when they reach maturity. Mollies chew at the fins of other fish to show their dominance, so they should not live with fish that have long, flowing fins or low tolerance.