I've read a lot of accounts that all say, "never stock Crappie in a pond. They will take over". I've had an ODWC biologist say the same thing.
You need some good predators to take out Crappie when they're over-populated. My "home lake" is full of stunted Crappie. 4 - 5 y.o. fish that are about 6" long. By the thousands. LMB's will eat the fry, as will Hybrid Striped Bass (stocked in the lake, but to many go over the spillway), Flathead Catfish, and Saugeyes. We're trying to get ODWC to stock some Saugeyes in that lake, but they are waiting on a long-term project to be completed. Flatheads, unfortunately, while voracious, are actively targeted by fishermen, and they rarely do catch-and-release on those monsters.
The best predators for over-stocked, stunted, Crappie are people! Just do the cut-and-gut routine, then cook the bodies whole. I just wish my wife would eat them. She will only eat fish fillets, and I'm not filleting fish that small. I've heard the small fish also make great fertilizer for a garden.