Fishy

Grow yourself to a bigger fish by eating the small fishes, but don't try the bigger ones or you will get eaten.
This is the most popular undersea adventure and fun game around. It’s getting pretty crowded down here, and if you want to last in this underwater arena, you’ll need to outsmart and outmaneuver the larger predators, all the while building your strength by eating any smaller prey you can find. All you need to know to become the big fish in the pond is a working knowledge of the arrow keys. The pond is yours for the eating. It’s up to you to feed or be fed upon.

http://www.tutorialsto.com/flash/games002/fishy.swf