I have had a pond for 15 years and up until this year have only lost 2 fish; both of which I found floating in the water. As of March 2009 I have gone from 33 fish to 9. From June 20th until June 21st, 6 fish (Koi) have disappeared. They were not floating and were no where to be found. Does anyone have any reason or what can be happening to the fish.