Edit,
Not sure its the same in a pond as a lake, but in my local lake if they can fit in it, they will spawn in it. I hand grab catfish in mostly water heater tanks. I have caught 50# fish in a 40gal tank. There tails would be hanging out, they couldnt even turn around in the tank. I would do like Snrub suggested though and put them all on bottom rather than stacked. Also, this only goes for Blue's or Flatheads. I have never caught a CC in a tank by hand.
