Live-bearing fish are the species that don't lay eggs. The most common aquarium livebearers include freshwater species guppies, mollies, platies and swordtails. These fish are active, colorful, hardy and easy to breed in captivity. Less common live-bearing species are much more difficult to care for, suitable only for advanced aquarists.
Guppies are probably the most common freshwater aquarium fish species. Their hardiness and friendliness make them ideal for beginners. They are prolific breeders, with females giving birth to as many as 60 live babies at a time. The varieties of guppies are differentiated by their coloring and fins. Common varieties include veiltail, lacetail, glass, redtail, and peacock. Males typically are more colorful and have larger fins, while females are generally larger and plainer.
You can keep one or two guppies in a 2-gallon tank, but they prefer larger groups in a larger aquarium. They enjoy a tank with live plants and require a basic filtering system and heater. They eat a variety of food including flakes, pellets, zooplankton, brine shrimp and frozen food.
Mollies are common livebearers suitable for beginning aquarists. Mollies average 2 to 4 inches in length and come in two major types -- short-finned and sailfin. Both types come in various colors, primarily black, orange and green. The minimum tank size for mollies is 10 gallons for four to five fish. They are prolific breeders, so unless you want to raise mollies, try to get only one gender. Males are slender and longer finned, while females have rounder bodies. This species of fish prefer a slightly salty environment, so add a teaspoon or 2 of aquarium salt. Like guppies, mollies like a variety of foods, so give them flake, frozen, freeze-dried or live foods twice a day.
Platies are similar in care and appearanceto mollies, but slightly smaller. Varieties include the red wagtail, the sunset and the tuxedo. Females are usually longer than males, with rounder bodies. A single platy will do fine in a 5-gallon tank, but more fish will require a larger tank. The species prefers a slightly alkaline tank, so keep the pH between 7 and 8. Platies can survive on nothing but flake food, although they'll be healthier and more colorful if fed a variety of food types.
Swordtail fish are easy to care for. They come in a variety of colors and can grow as long as 5 inches. Males are identified by their swordlike tails. Swordtails are very active swimmers, so they require a tank size of at least 10 gallons. Keeping more than one swordtail will require a larger tank. Males can sometimes be aggressive, so a good mixture is one male per three females. Females will give birth about every 28 days. Swords can adapt to a wide variety of water conditions, and like the other livebearers, will eat most any type of fish food you offer.
Although there are many fish species that give birth to live fry, few are suitable for an aquarium because of size and environmental requirements Four livebearers that you can keep in an aquarium are halfbeaks, splitfins, freshwater stingrays and Anableps, also called the “four-eyed” fish, because they float at the water’s surface with the top of their eyes above the water and the lower half beneath the surface so they can see both above and under the water. These species are less hardy, more difficult to maintain in captivity, and not recommended for beginners.