I would Remove every crappie you catch !!!! size does not matter pretty soon you will be catching 30 or 40 6 inch crappie and few over 9, unless your pond is greater than 20 or 25 acres. 1 mature female crappie will lay over 50000 eggs. if 1% survive to maturity that's 500 new fish from ONE laying. If half of them are females then when they spawn that's 250 X 50000=12500000 and 1% of that is 125000. you see why Biologist and county agents DO not recommend Crappie in ponds. Maybe the pond is heavily fished so the population of fish is being slowed down some and will continue to produce good amount of keepers