I leave my guppy fry in the same tank as the adults and scoop out a few adults now and then to pass along at club auctions. I find that with adequate cover and generous feeding, the adults allow a large number of the fry to survive any predation. If you are intent on saving every fry, you will need lots of big tanks and will want to segregate the females into a tank of their own before they drop fry. I do that once in a while with mollies but usually do not because I have only 25 tanks and have no room for that many fry.