We have a few large giant female NP in our pond (5 acres). We also have quite a few giant CGC. These are out "Management Fish". The NP help keep populations of everything else down and the CGC keep the bottom of the pond clear of decaying plant and animal material. Both are great fun to catch and release.
Our pond is 80-90% percent sand and gravel bottom so the CGC can't stir up the bottom slurping for organisms or plants. In a pond with less sand and gravel CGC could be a real problem.
There have been no small NP nor CGC seen in the pond for years. Neither of these fish are successful at reproducing. I believe the CGC do produce young. Carp minnows are yummy to most every other fish in the pond; hence young don't survive.
Fish management people will see everything that is wrong with having these fish in a pond, but it works for us.
