Platy Fry

Question
My son had 2 Plates and then one died.  We thought he had 2 boys, but we were apparently wrong and Sunny left a legacy! You can imagine our surprise when we woke up one day to another fish in Oscar's Tank.  Only one though!  I removed the plant and ship from the tank to look for more fry and there were none.  2 weeks later...one more.  three days later... one more.  Every time we find one they are super tiny.  All 3 babies are different sizes now.  ie..small, medium, and large.  Is it normal for a platy to just 'pop' out one fry at a time every few days, because you can tell by their sizes that they are not the same ages.  I have a 5 gallon tank and until 2 weeks ago it only contained 1 fish and 1 snail.  How may fry should I expect to finally end up with?

Answer
Hello Monica,
Platies are live bearing fish that can stay in pregnancy for up to one month. It is very possible you had some fry that you didn't know about before the other fish died. They normally have all their babies at once, and the fry are very good at hiding. It's very easy to miss them - especially if you don't know to look for them! Also, when a live bearer spawns, the majority of them can hold the sperm for a few months afterward and "appear" to be having babies on their own.
With all these new additions, you'll want to upgrade to a larger tank. At least ten gallons. I would definitely recommend separating the males from the females as soon as you can tell, to make sure you don't end up with a thousand fish you're not sure what to do with (the females can have up to 50 fry at one time).
You can tell male from female by their anal fins (the fins on the bottom, on their stomach close to the tail fin)
Males will have long, skinny anal fins while females will have broad, triangular anal fins. Males will also usually be chasing the females around  (though sometimes it's vice versa)and more often then not females will have the larger bellies - even when not pregnant.
Lastly, you will want to keep fry that you want to keep alive away from the adults because they will sometimes eat the fry.