The small fish are more populated than the larger fish
The larger fish are favorable over the smaller fish, helping them survive the predators
The predators start to fill the water, eating the smaller fish so their population is smaller and the large fishes population is larger
The larger fish survive longer than the smaller fish
The larger fish reproduce faster, making the larger fish more populated now than the smaller fish
Due to the size difference, the predators are able to eat the smaller fish, making them more populated than the smaller fish. This is the adaption they have to the new environment of predators.