Finding Nemo cheats and cheat codes for Gamecube

Press the following button combinations at the title screen after
pause game play to access the the cheat options.

Credits: 
Y, B, X, Y, Y, B, X, Y, B, X, Y, B, B, X, Y, B, X, Y, B, X, X, Y, B, X 

Invincibility: 
Y, B, B, X, X, X, Y, Y, B, B, B, X, X, X, B, Y, X, X, X, B, X, Y, X, X, B, 
X, X, Y, X, B, X, X, X, Y 

Level Select: 
Y, Y, Y, B, B, X, B, Y, X, B, Y, B, Y, B, Y, X, Y, Y 

Hidden Level: 
Y, B, X, X, B, Y, Y, B, X, X, B, Y, Y, X, B, Y, B, X, X, B, Y 

Secret clue
While on the Mount Wannnahockaloogie level, look for an old brown sign. 
Dart behind the sign to score an important clue.