Goldfish, evolution, adaptation and breeding

I'm pondering and suspending the answer to those questions, my belief remain intact, only my huge and deliberate curiosity have force me to suspend the answer. Perhaps readers and researchers out there can give some more clues. The example i put here may triggered my curiosity.

The goldfish and koi are from same family, carp. 
After thousand years of breeding, mutation and perhaps adaptation to environment. the above genetic fault or mutation may lead to new hybrid? no one can give the answer until it really happened...

The varieties of goldfish and koi  can be trace back to 'humble' crusian carp and prussian carp. Mutation of colour, interbreed and perhaps evolution leads to varieties of those domesticated fish.