Dan, the original HBG stocked are the only fish that will grow to a larger size. The parent HBG will reproduce, but mostly male offspring (around 95% male) and the offspring are VERY inferior (DNA damaged) than the parents.
What few female offspring produced from the original HBG parents that spawn with the male offspring (or original male HBG)revert back more toward the Green Sunfish (GSF) that the originals were crossed with.
Now, for the benefit of our beloved member Jhap,I have to say that GSF are beautiful fish and prolific breeders. I also have to say thaat GSF are a nasty little pest in a pond, but stunted offspring from HBG are even worse. The GSF will quickly produce so many fish that there is simply not enough food in a pond to feed all of them and they can't grow much...thus they stunt, usually at around 3 inches.
Three inch fish are great forage for a bass 9 inches long, but too much work to catch for the calories gained for a bass 12-16 inches long. The bass in that size range do not have a fish near the size to make it grow so they merely survive on the small fish and never grow bigger.
If needed, adding pure northern strain (aka straight) bluegill will allow your forage base (the bluegill) to recover all size ranges your bass need to grow properly. Unlike a HBG, BG will produce equal numbers of males and females and LOTS of babies of equal quality to the parents for the bass to eat. The babies that survive will grow as big or bigger than the parents.
