There are actually two different species of fish that are collectively referred to as mollies; Poecilia sphenops and Poecilia velifera. Mollies are members of the family Poecilidae which includes southern platyfish (the plati) and swordtails. They are native to the Americas. They can be found in the Southern U.S., Central and South America.

Mollies are often found along coastal waters. As costal dwellers, they prefer a small amount of salt in their water. The standard recommendation ranges from one teaspoon to a tablespoon for every five gallons. Split the difference and play it safe. If you only have experience with freshwater fish you should be aware of the fact that salt does not evaporate with the water. You will only need to add more salt during water changes. Iodized table salt can kill your fish. Use only aquarium salt. Interestingly enough, mollies can be found for sale in both the fresh and salt water sections of fish stores. Mollies can survive either or both if acclimated slowly to their new environment.

Mollies come in a variety of colors and body markings. The selective breeding of mollies has yielded Sailfin, Balloon, and Lyertail varieties. Male mollies have an enlarged dorsal fin and a modified anal fin known as a gonopodium. An adult molly will grow to a length of about four inches.

Two species of molly P. sulphuraria (the sulfur molly) and P. latipunctata (spotted mollies) are listed as critically endangered in the wild.

Mollies are mild mannered. They make good community fish provide they are kept with species that are not adverse to a slightly salty environment.  Mollies enjoy heavily planted aquariums. They like to hide in the plants.

Despite the numerous locations they are native to, mollies prefer slightly alkaline to neutral water with a temperature range between 77-83°F. They have a life expectancy of up to five years.

Mollies are omnivores, eating both plant and meaty foods. They will readily eat flakes, freeze-dried, frozen, and live foods. You should try to include some plant matter into their diet.


Mollies are live bearing fish. Males will often harass the females of their own species. To help insure a low incidence of domestic violence, it is best to keep two or three females for every male.

Mollies, like most live bearing fish, are easy to spawn in captivity. Live bearing fish engage in internal fertilization. The male uses his modified anal fin, the gonopodium, to inseminate the female. The gestation cycle is around 60 days. A typical brood rages from 20-50 fry.

Mollies will eat their fry. To avoid this, the adults must be removed from the breeding tank after spawning. Or you can use a breeding trap. Breeding traps are frequently used when spawning live bearers. They are comprised of two compartments. Place the mother in the top compartment. The fish will drop through to the bottom compartment. Remove both adults and release the fry into the breeding tank. Breeding traps are inexpensive and can be purchased at most fish stores.

Baby mollies can be feed newly hatched brine shrimp, or powdered fry food. An economical alternative is powdered eggs.