Eric summarized well the topic of northern and southern strains of BG. His quote of: "the most important factor to growing nice bluegill is to be sure they have enough food to eat and not to much competition" is VERY important. Many pondowners do not fully understand this key factor for growing most all species of fish so they reach their full potential. In many instances, crowding results in slow growth. Lack of food due to too many fish results in food shortages for the desired species that are over abundant resulting in slow or reduced growth. Natural food reserves in a pond are not limitless. Each pond has a set amount of natural fish foods that it will naturally grow or produce. Manufactured fish foods and/or fertilizers can increase or boost the overall productivity of a pond and enhance the fish biomass. Then the 'trick' is to know or learn how many fish will best utilize the available food supply.
Performed or managed correctly, the northern strain of BG can regularly and easy produce numerous individuals in the 9"-11" range. For more reading about growing big BG check out this link from the PBoss Archives:
http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=189988#Post189988
