Half-fish can be hard to find as they're usually in the third chao box of some levels, but there are some that are more easily obtained. In Green Forest, beyond the second checkpoint and after you swing on the vine, check around the wooden boxes for a half-fish. From that point, jump on the small floating platforms to the left; on the third, stationary platform, whistle near the flowers to make another appear. In Egg Quarters, you can use the bombs thrown by the Kiki monkey robots to break open metal cages containing other half-fish.
~ Crazy C Lea