Another item - Shorter life span may not actually be due to fatty livers but some other unhealthy items in the food that shortens the life span; maybe too many carbohydrates?. How many carbohydrates and excess fats do wild BG have in their diet????? Research by Dr. Griffin is likely dated and maybe not a complete biochemical, physiological workup of the fish was performed. Maybe the study was primarily a growth study comparison. Are the research methods for that study available for reading? I doubt very much the longevity of the fish was considered when Dr.Griffin conducted his study. Plus I doubt other food manufactures consider life span when developing food formulae.
While there must be carbohydrates in fish food, bluegills can't metabolize carbs. Carbs in fish food designed for carnivores are there to help physically hold the pellets together. While some fish do metabolize carbs, as catfish, carp, and tilapia, carnivores don't need them. Dr. Griffin's research had two primary objectives. First, he studied growth rates. Second, to a lesser degree, he studied livers to determine fat amounts. A lesser objective was to figure out the best vitamin and micronutrient package for carnivores. He did this in 2006-07.
One thing to keep in mind, everyone...even with the best fish foods, feeding your fish is supplemental. There's not a bluegill in a recreational pond anywhere that is solely dependent on fish food. The dynamics of what happens in an aquatic environment precludes that assumption. Bill Cody can feed the "best" fish food he wants, and only some percentage of his fish will eat as much as they can consume for those few minutes. Think about it a little more deeply and we can safely conclude those fish get a meal for about three minutes, maybe three times per day. Depending on the temperature, they'll digest that food within 4-6 hours. Since the food is designed to be digestible, it may happen faster than that. Between feedings, bluegill are still what they are, or why would they bite a bit of night crawler on your hook? They continue to feed, at every opportunity.
Dr. Griffin did not do a complete physiological or biochemical workup. Their research lab is designed to create the best feeds, not make fish run on a treadmill. No feed manufacturer does that, to my knowledge. And, no any proprietary research isn't available to the general public. Heck, even the state where I live, the Parks and Wildlife Department won't share their largemouth bass genetic work, and they are publicly funded.
Here's my bottom line about this subject. I rarely saw two-pound plus bluegills until Purina developed their AquaMax line of fish foods and improved the formulation in 2006-07. By 2010, I was seeing many, many two pound plus fish. I directly attribute that fish food to boosting the nutrition of fish in the lakes where it's been fed. Not only did bluegills grow because of it, I've also noted an increase in aquatic insects, invertebrates, and other foodstuffs which bluegill eat. I attribute that, to some degree, to nature utilizing fish waste, uneaten feed, and a change in population dynamics of fish.
Lastly, I can't address any change in lifespan due to a fish food. In my opinion, I think many fish's lifespans have been increased due to feeding pelleted fish food. That's partly due to better overall nutrition available, but just as much because those parcel of the population didn't get eaten themselves because of an overall boost in the food chain.
One other comment...there is only some percentage, I think it's less than 20% of bluegill which survive long enough, that CAN grow into giant sizes. I think there's a propensity, if genetics and behavior allow it, for a fraction of fish to be able to grow to those sizes. All the fish food does is give them the opportunity.
