This link could be helpful:

"Israeli coloured Ghost koi and ghost carp are the same fish and are carp hybrids, the result of a cross between a metallic koi and a common carp. NB This is not a hybridisation between species but between varieties of the same species producing fertile offspring. Recognising that koi are the same species as carp (Cyprinus carpio) and it is through man's selective breeding that koi occur in an infinite array of colours and patterns, it is not surprising that a cross between metallic koi and common carp produces viable offspring - ghost koi. These offspring exhibit 'hybrid vigour' where the hybrids outperform the parents' growth, fertility and health"

http://www.cascadekoi.com/Koi/IsraeliGhostKoi.aspx

Fishing has never been about the fish....