Goldfish are not going to breed in a 10gallon. Goldfish spawning is triggered by the changing of the seasons. As far as the size of the goldfish they are too small to be sexually mature if you have 50 of them in a 10gallon. And 50 is too many goldfish in a 10gaollon unless you are using them as feeder fish and have great filtration.
Mods this question has been answered. Please close this thread to avoid flaming.