20 acres is plenty big enough for blue cat. Keep in mind, though, they can quickly become the dominant predator if stocked more than about 20 per acre. They grow extremely large and are top line predators. I once electrofished a 52 pound blue cat which had eaten a three pound bass. So, be prepared for their large sizes. They can reproduce, once they are 4 years old, have a place to hide, and a place for baby blues to feed. Channel cats are fast growing, will reach sizes 10-12 pounds in a lake, can reproduce if conditions are 'right.' So, two fish with two different lifestyles and consequences. You get to pick.
