Black crappies in particular but white as well can do quite well on just invertebrates found in a pond. Dragonfly nymphs, damselfly nymphs, midge nymphs, diving beetles, water boatman, nightcrawlers and worms that get washed in, leaches, crayfish, etc...
The crappie in the photo had plenty of these to eat only competing with just the other crappies stocked and no other species in a 1 acre pond. Once the crappies pull off their first spawn, there will now be hundreds if not thousands of mouths to feed. The originally stocked crappies will feed heavily on their own offspring, but at their size, they'll only be able to prey on crappies up to about 3". Once that first year class reaches sizes above that, there will be little if any mortality. The remaining crappies which will number in the hundreds will now eat themselves out of house and home.
The first stocked crappies will have issues now as that once abundant supply of invertebrates is now gone because their offspring has eaten them all. Their offspring is too large for them to eat as well.
