To add to what bassmaster 61 said, I had an old pond over run with GSF. I turned it around by catching adult BG out of my main pond and putting them in the old pond. It took a couple years and now I can still catch some GSF but the BG by far dominate the pond. Putting in BG big enough the GSF could not eat was the key as at that time they were the only predators in the pond. I used all sizes but a significant number in the 5-6" range.
