Graham's got the right idea for koi,stick to proper fish in yer pond,roach,perch,tench,bream,crucian,chub,gudgeon,rudd,and a few mirrors.I helped my dad stock his new pond 5 years ago.We started with 2" roach and perch then gradually added a few of the other species.I find it amazing how so much natural life can establish itself in what's no more than a 'big puddle'.At the moment the perch go to 1lb,roach 12oz.,and the 4 mirrors are upto 3lb.(which were transparent when we bought them!).Great fun fishing on light tackle.Maybe that's why I havn't moved out yet!!