Its a complete mystery as to why the YP haven't taken hold, I have tried perch of a variety of sizes including some fairly large ones (over 10 inches) but the result has always been the same. Never have caught one, seen one or even found a dead one. I may give Golden Shiners a shot but i am not terribly optimistic give the smaller size and soft body. It would be better if the Pickerel had become established after some forage fish were already present in the pond but unfortunately it was this way when i got it.Rebreast Sunfish sounds like a great idea. Have you ever tried Pumpkinseed and are they any good? How about Smallmouth Bass (younger fish could provide good food) or Koi (have heard they get pretty large so younger classes might provide good food)
