How about making the yellow pill an "Evolution pill" as in if you find one, you can change into a different kind of fish (or bird) permanently or for a short time (like the wings). Also, try to get it to work that after a certain amount of points your fish grows, or that a "pop-up" comes which lets you choose some evolution path: Faster, Bigger, that kind of things.
Also every time you evolve you should get a bit extra, like a few fins or something like that.
A nice game and it has potential :)
The graphics were great and the game ran smooth, keep up the good work :p