Just a input as there is no possible way by looking from that angle if it is a KOI hybrid. BUT that being said I would say it is more likely a pure comet. It looks like a really long finned sarrasa. I've seen Koi goldfish hybrids and never seen one that took on that look, I have however seen MANY long flowing fin Pure Comets and Shubunkins. One way to get a better idea if it's a hybrid, Look for barbels on each side of the mouth, Koi have them Comets don't, If it is a Hybrid in most cases it will be the Koi that survive as they will eat their own, gold fish do this less and in most cases when the to hybridize the comet side doesn't survive.