A friend if mine has some blues in a 1.4 acre pond that is fed by a small very rocky creek with about 300 acres of watershed. As far as he can tell they have never spawned. He put them in at about 1-2 pounds or so, wild caught. I have seen some that appeared to be 12-15 pounds up in the edge of the feeder creek. Friend says some will go 20 pounds. I was fishing there for BG with ultralight about a year ago. I had about a 7-inch BG hit the lure, fought it for maybe 10 seconds, when something took the BG and went out into the middle of the pond, screaming my drag. It finally let go, and I pulled in a roughed up BG. I think that was one of the blue catfish. They are by far the apex predators of that pond.
