The largest fish in the world eats almost exclusively plankton. And don't forget the silver and bighead carp, both exclusive planktivores.
Notice the body shape and the size of the eye. Compressiform fish are not highly adapted predators, they are not very fast. Crappie are adapted for manuverability, tight turns and fast stops. The large eyes of crappies allows them to see small prey easily. In effect, they are adapted for precision feeding.
Crappies might exclude bass and other predators by consuming all of the zooplankton, not by eating age 0 bass. Because they hatch early and eat lots of zooplankton (especialy when small) they may actualy eat so much zooplankton that there isn't enough food for LMB or BG fry to find food. It is critical that fry are able to find a good zooplankton meal soon after they hatch.
BG have been documented to prevent successful walleye hatch at densities of 50kg/ha or about 43lb/acre. Most likely they do this by eating all the zooplankton.
