There are two species of Platy, Xiphophorus maculatus, and Xiphophorus variatus. Platys are closely related to Swordtails, Xiphophorus helleri, and Xiphophorus maculatus will freely interbreed with Swordtails. The interfertility of Xiphophorus variatus with the others two species may be less, but hybrids can occur. The Platies and Swordtails we buy are often not of pure species.
All three species come from Central America. Xiphophorus variatus, commonly called the Variatus Platy, appears to be able withstand slightly colder conditions than the other two species, and may be more suitable for an unheated tank in a reasonably warm house than the other species, but all are basically tropical fish.
Platies tend to be shorter but thicker than Swordtails.
The platy is a tropical fish and I recommend a temperature of 24̊ C (75̊ F). They prefer harder water with some salt in it although they are quite adaptable. The platy appears to be better able to survive higher Nitrite (NO2) levels than most fish, but these should normally be avoided for all fish.
The Platy is an omnivore and will eat some algae as well as live food including Mosquito larvae (wrigglers) and Daphnia. They do well on all normal fish foods.
The Platy is a peaceful fish and is a good fish for a community tank of small peaceful fish. The Platy lacks the long fins of the Guppy and is a faster swimmer, so its companions can include some of the slightly aggressive fish that you would not put with Guppies. You need to avoid any large, aggressive or predatory fish.
Suitable companions include Swordtails, Rummy Nose Tetras, Harlequin Rasboras, Lemon Tetras, Neon Tetras, Flame Tetras, Buenos Aries Tetras, Black Widow Tetras, Cardinal Tetras, Emperor Tetras, Head and Tail Light Tetras, Glass Bloodfin Tetras, Glowlight Tetras, Guppies, Endlers Guppies, Neon Tetras, Peppered Catfish, Siamese Fighting Fish, White Cloud Mountain Minnows and Zebra Danios. Not all these common companions are compatible with each other. Most of these fish will eat baby Platies.
The platy is very easy to breed. The ideal sex ratio is probably one male to each three females. They have live young, and the babies tend to be vigorous. They will grow much faster with suitable size live food although they can be raised on commercial dry or liquid fry food. The water conditions are not critical. The parents, as well as most other adult fish will eat the babies.