LMB, gar, bullheads, greenies....all bad choices IMHO. I have/had all of those at one point and I can't see it working. LMB killed my first pickerel. Bullheads grow big and fast and would probably atleast TRY to eat your pickerel(pickerel are slender and many fish consider them a meal eve at equal size. and if the pickerel is bigger well it goes the other way around). Greenies are too aggressive IMO and would pick on the pickerel. I would do either a pickerel community or like drew said pumpkin seeds or o-spots....Community is probably the best IMO. Bichirs might get gobbled up if they aren't big enough too. My 8" grass tried to eat a 6" irridescent shark once and it was thick. I think you could easily do 6-8 pickerel in a 200(depending on demensions...can we get those please?)
Chad