To go to bonus rounds (in Six Clams adventure Land), you must get the % of spatulas in every Chapter as the following:
Chapter 1: 60%
Chapter 2: 70%
Chapter 3: 80%
Chapter 4: 90%
Chapter 5: 100%
When you're near the end of the final level in a chapter you will have to beat a boss. Here's how to beat all of them:
Mother Jellyfish: Throw jellyfish at her or butt bounce her.
Sub-Shark: Find the jellyfish launcher in the middle of the arena. Use it to shoot jellyfish at it. There is a re-loader at the right of the arena.
Parisitic worm: When it gets near you, jump or butt bounce it. Butt bouncing gets better results.
Flying Dutchman: Like the Sub-Shark, you have to use the jellyfish launcher but this time you have to do it faster because he disappears and reappears.
Dogfish: Jump on the levers to turn him white. When he's white, butt bounce him!
When you get to the part where you knock down the wall and Gary follows you, do not break the wall. Instead, get rid of all the obstacles. Then go back and talk to Gary. Now you won't be responsible for him. When he gets to his food, claim your prize, 1 free life!