Relasing any non native fish anywhere including flushing is bad for the fish and environment. That said, the guy could probably just give these fish to any petstore to rehome too.
As for culling fish.... at least the ones we get while fishing to eat, are bonked in the back of the head with a "beat stick" and they are out like a light. You'll be able to tell because the entire skin will shiver a bit and the eye will no longer try to look "down".
As for culling fish.... at least the ones we get while fishing to eat, are bonked in the back of the head with a "beat stick" and they are out like a light. You'll be able to tell because the entire skin will shiver a bit and the eye will no longer try to look "down".