I've found it's a good tactic to keep one of each type of fish body (goldbulb, firearrow, carp etc etc) and then try to arrange it so that each type of fish has a different fin (e.g. pink goldbulb, crimson firearrow, oriental carp etc etc). That's (I think) 21 fish in total). If you can manage to make that collection, you'll be able to breed just about anything you want from those fish. Of course, you may not know exactly HOW to breed anything you want, but it will be possible ;-)