[Cavan Allen]

The snails are indeed Neritina natalensis. They do breed in fresh water. The ones that don't are N. reclivata, a brackish snail native to Florida. Everyone seems to have them in Canada, but they are apparently quite difficult to obtain in the US. I'm still working on it myself...

http://perso.infonie.be/pomacea/neritina_natalensis_uk.htm