Several months ago I started with 3 Platies, now have 14. Mickeys are funny. Swordtails will interbreed with Platies. You need to keep 3 females to one male, and the male will be all over the female who's in breeding condition, chase her all over the tank. They're like rabbits! The male's anal fin is very skinny compared to the female (her's is wide). Females can store sperm in their body for a yr. so if yours is getting fatter, its likely pregnant. Do keep the water changed and then add recommended drops of Ick & parasite prevention, keep on the warm side, feed only as much as they'll eat in two min. They'll nibble on live plants too, also drop in tiny pieces of raw hamburger, salmon or tuna shredded in your fingers and watch 'em turn into lil' pirhannas! lol. There's lots of websites how to care for Platies. They don't eat the fry so much if you feed mamma more when she starts to guard a spot in the back corner or under the plants. The fry will escape and hide fast into fernlike plants. Good luck!