The purpose is that you gotta stop the purple fish from getting to the bottom. So the yellow fish has to stop the purple fish. If the yellow fish touches the purple fish, the yellow fish gets a point. The purple fish scores by getting to the bottom where there are eggs that he wants to eat.
There are always fish that want to eat eggs. Trout lay so many eggs so at least a couple of them survive.
Controls for the purple fish:
a - makes you go left
d - makes you turn right
Controls for the yellow fish:
left arrow - makes you go left
right arrow - makes you go right
Have fun controlling fish!
Click here to play this game.