For avid fishermen and anglers, the largemouth bass is a favorite freshwater fish with an appetite for minnows. Once fish evolve the size and speed needed to become top predators, natural selection keeps them in an evolutionary holding pattern, a new study finds. A new study finds that once they evolved to eat other fish, largemouth bass and fellow fish-feeders have remained relatively unchanged compared with their insect- and snail-eating cousins. As these fishes became top predators in aquatic ecosystems, natural selection put the breaks on evolution, say researchers.