The size of adults depends on the original breed: in Poecilia sphenops females grow to about 10–12 cm and males to about 6–8 cm. For example, Poecilia sphenops representatives are usually relatively small, while lyretail varieties, descended from Poecilia velifera, sometimes reach 20 cm. Given this, when choosing the aquarium volume, one should base it on the maximum possible size of the fish: for a group of 3–4 individuals, an aquarium of 100–150 liters or more is recommended. An important part of aquarium decor is the presence of dense thickets of aquatic plants, which create shelters for smaller or weaker fish, as well as for fry. Additionally, some plant species can serve as an extra food source, so it is advisable to choose fast-growing and undemanding varieties. Optimal conditions for keeping Mollies include warm, slightly alkaline water with high general hardness. Although selectively bred forms have adapted to softer water, such an environment is not the most favorable, especially during breeding. It should be noted that Mollies are naturally adapted to living in brackish water, as their wild ancestors are often found in river estuaries – zones where fresh and saltwater mix. However, in a home aquarium, caution should be exercised when adding marine salt, especially for beginners, as there is a risk of exceeding the concentration, and other inhabitants may not be prepared for increased salinity.