Mollies are very good starter fish. I have a Black Lyretail Molly and personally I think that even amateurs and people with alot of experience should get one of these. Here are some of the species of Mollies:
Lyretail, Sailfin, Dalmation, Short-finned, Platy(Moons), etc.
Black, Silver, etc.
'black mollies are the best and most friendly black fish in the world'
They require at least a 15 gallon tank, and are livebearers. So if you keep both male and female together, they WILL spawn. And also, since they are livebearers, the fry are born free-swimming.
The Molly is a tropical fish that prefers a little salt in their water. A teaspoon of aquarium salt per 5 gallons of water will go a long way in helping them. The molly is a very attractive tropical fish that comes in many different colors such as orange, green and black. Some of the more popular varieties include the sailfin, balloon and the dalmation.
The Molly fish is a livebearing tropical fish that can be fairly easy to breed. For many aquarists the biggest problem is not getting them to breed but stopping them from breeding. If left in a tank with other adult fish, the baby mollies will get eaten.
Mollies will eat flakes, frozen, freeze dried and definitely live foods.
Scientific Name : Poecilia sphenops
Common Names : Black Molly, Lyretail, Sailfin, Liberty, Mollie, Pointed Mouth, Short Finned, Mexican, Golden, Piebald, Ghost Pearl, Gold Dust, Red Sunset, Dalmation, Ballon, etc.
Care Level : Easy, very good for freshwater beginners if keeping a single sex. Keeping both sexes could cause problems since this fish is such a prolific breeder.
Size : 2 to 4 inches (5 - 10 cm) depending on the species
pH : 7.5 - 8.5
Temperature : 70°F - 82°F (21°C - 28°C)
Water Hardness : 10° to 25° dH
Origin / Habitat : Central America
Life Span : 3 - 5 years
Molly Fish Temperament / Behavior : Peaceful
Tank Size : 15 gallon minium, prefer tall aquariums
Molly Fish Compatible Tank Mates : Not many - some feel they should only be kept with others of the same species.
Molly Fish Disease : Freshwater Fish Disease - Diagnose, Symptoms and Treatment
Diet / Fish Food : Give them a varied diet consisting primarily of flake foods but supplement with live and freeze dried foods occasionaly.
Tank Region : All over the tank.
Gender : Males are more slender, females more round. Males also have a modified anal fin.
Similar Species : Livebearers
Info from FishLore.
They like some salt in the water, and can, if accimated properly, become saltwater fish.