For those who can't go to the very end of the game to find this secret, here's the bonus game the second secret tunnel leads you to: http://www.4urentertainment.org/joe/joe-final/
Minigame/New map Idea: Have you every played those games where you eat everything smaller than you, and avoid everything that's bigger? That's the idea, in this case, we catch fish, as we get bigger we can catch the more valuable fish(Ie: whales, dragonfish, etc.).