We have black crappie in our 1 acre pond and they do pretty well. Pond is about 15 yrs old and the average crappie we catch is around 11 or 12 inches with a few up to 15 or so. We make sure to keep quite a few (80-100 usually) each year and I think that helps keep the size up. There were a few years early on, when we didn't keep many and the average size was a lot smaller, like 7 or 8 inches. We also have a good largemouth population to keep them in check and like JCD, we don't harvest any bass.
"Give me crappie, or give me death"