I've played Fish Tycoon for some time now, so I eventually figured out all the "perfect fish".... even though I do have my favorites that aren't quite perfect.
I found them the hard (but enjoyable) way, but since Buttoneer put out that really nice spreadsheet, I can see that it makes it even easier to figure out which fish are the "perfect fish", in addition to finding the "Magic" fish (which aren't all "perfect", by the way).
It helps if you already know what some of them are, which obviously you do. So here's the trick to using the spreadsheet...
Say you want to find out what fin the Pigmy has for sure. Take a known pair that would make a Pigmy... Beta and the Bananafish, for example. Now, if you know their "perfect" fins for those fish (Greenfin and Flagged in this case), line up those fin colors together on the Fin chart, and there you have the fin for the Pigmy!
Only problem is, that won't help you with the Spotanus, as nothing but a Spot makes a Spot... and finwise, nothing but a Twin-fin makes a Twin-fin. (hint hint)