The fish is simply a gif file, but the most life-like gif file you'll ever see.  You can buy food, clothes, shelter, and other items to keep your fish alive and happy.  Using breambucks, of course.  Every time you do something nice for bream, you get breambucks to buy fish stuff, and eventually other stuff.  Eventually features will be added that allow you to battle other fish, take your fish for a walk, and other stuff like that.  I'll store all the information for everyone's breambucks and fish on a gargantuan word document, and send you your info on request.  Currently, for example, Bella and Datsun has around 20 breambucks, and SoCrates, for winning the Bream Award of Excellence, has 40 breambucks.  As you can see, they'll need more if they want to achieve the Final Bream.  Once you purchase a fish, your breambucks will not deplete, but will be stored in another file representing how much effort you've put into your fish.  Eventually, you will have enough experience points, if you will, to evolve into another fish.  Different fish look different, have different powers in battle, and stuff like that.  Now, buy your fish.