I think it may depend on how the crappie got into your pond in the first place. If the only crappie in there were stocked by someone, you can probably fish them completely out. But it may take years.
In my pond, we'll never get rid of all the crappie. They come in through the stream that is part of our water supply so, I have no control. I can't complain too much - all our fish have come in through that stream. The only thing we've ever stocked are the golden shiners. I think we've lost a bunch of those through the overflow (not to mention the natural predation). But, golden shiners are native to Georgia so it doesn't hurt the ecosystem here if they do escape.
Tilapia are illegal to stock in Georgia right now. I doubt I could afford to stock them anyway but, Georgia law does not allow anybody to stock tilapia in any BOW anywhere in the state.
