This Game is a really good game, in terms of gameplay, amongst others. I really like the background music and I think that the game is possibly the best game in this kinda category that I've played in a long time.
As mentioned by some others, the fish should really grow bigger as you eat more, since it is natural, and it would improve the game. (instead of constantly running from those bigger fish.)
Yellow pill.. well, I think the yellow pill should make the fish "evolve"into a bigger form, perhaps looking a bit different to make the game a tad more instersting.