I think you would have to follow the "new book" on doing everything you could to acclimate the new fish to the pond....blocking nets, removal of many numbers of the other predators...baitfish stocking prior to the new stocking...just everything you can do to amp the chances of establishing new populations.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."