After finding the 7 Magic fish, you can find the 21 "Perfect Fish" (that's the body with it's right fin type) and go to the extreme of finding the 441 total possible types of fish. (That's 21 bodies each with 21 types of fins) The statistics keep track of how many of these you have found, and their is such a wonderfully silly sense of accomplishment in creating all of them.

It's still keeping me busy after a month of extensive playing.

Plus I do love just taking care of my fishies, too!