The main thing with these clams is that they reproduce like crazy and they do have an aversion to colder water. So, their population can vary widely.
Redear sunfish will eat them. Channel catfish will eat them. Crayfish will eat them.
You also have to consider that they are filter feeders too. I know that the introduction of some species, like zebra mussels, to non native waters have caused problems by making water too clear.
Overall, I believe, that if you want to introduce a species of clam into your pond you should try to find some fingernail clams. They stay smaller, have softer shells, and make a better meal for the fish in your pond as they never get too large to be eaten.
