Remember how Nemo had a smaller pectoral fin? Koi has that too. His left pectoral is larger than his right, and the funny thing is that my unnamed white EE's pectorals are close to the same size, not exactly the same, but close.
So.. does that mean he could have come from an EE breeding?
Lastly, unless Koi is really young, I think he's a HMPK, his tail ins't long like a HM's, it's short like a PK but when he flares you can see the correct HM shape.
Thoughts on his tail type and pectoral?