My first comment to such posts is to say that these small snails (bladder, pond, Malaysian Livebearing) are your best friend in an aquarium. They can get everywhere and eat all organics (fish waste, dead plant matter, some algae) which breaks it down faster for the various bacteria.
Snails will be in numbers comparable to the available food. And given the above, this is much more than just overfeeding fish foods, but that will obviously increase them too.
Eggs from bladder and pond snails are laid as small gelatin-type masses on surfaces like the tank glass, plant leaves, etc. So I seriously doubt a pleco moved to another tank would take eggs. The eggs hatch into very, very tiny snails though, and it is easy to move those with anything wet.
Byron.