I had an angelfish years ago that learned how to scarf snails. For every snail I disposed of, 3 would take its place. After a while, I just smashed the buggers against the glass. At first, the angel would move away then come back later to investigate the 'smutch'. He (or she) would pick the meat out with relish. Eventually the fish learned that when I put my hand in the water, a tasty snack ensued. He would drift over and watch the snail fixedly until I smashed it. He would suck the whole snail in and somehow manage to swallow the meat and spit the shell bits out.
After a while, he got to the point he could suck the snails out of the shells and/or crunch through the shells. This lasted until he ate the two large 'breeder' snails. End of snails, end of treats.. Oh well, it was fun to watch while it lasted.