I had the Israeli carp living with the KOI for 15 years and I never saw one off spring or hybridization in that time. I'm sure the bass, bluegill and White Amur grass carp were controlling the offspring. My Israeli carp I estimated to be 30 inches long and about 15-20 lbs while the KOI were in the 2 ft. range and maybe 10-15 lbs. The mirror carp picture in the book I am reading "Small Scale Aquaculture" looks very much like my Israeli's and I wonder if they eat filamentous algae as mine did. If you have the Israeli and the KOI in this pond I am curious if you have any FA pond scum. With them I didn't and without them I do for the first time. This is what my Israeli looked like.