Giant Bluegills- Genetics of Plasticity? Do Some Bluegills Grow Huge Because of Genetics, or Environment?

 “I have often considered there hasn’t been enough study about bluegill genetics. I would guess different strains exist around the nation. I’ve seen native strains I think have evolved in small streams. Their bodies are long, and they don’t grow large. They mature as small as two-inches and bellies full of eggs that look like they’ve eaten a strawberry. For stocking a fishing pond, I’d prefer a strain where food is used for growth, and not reproduction. Could this be a Pond Boss story?”    

This question came across my desk recently from Dr. Richard O. Anderson, famous fisheries biologist and educator who developed largemouth bass relative weight tables that the professionals use to this day.

Thinking about that question, I drilled it down to this, “Do bluegills adapt to their environment, or is their behavior and performance inherited”? Could it be both?

Could those bluegills in a neighboring stream have offspring which could grow to large sizes in that pond one hundred yards away, or is their destiny similar to their parents?

When we stock a pond or lake, how important are the genetics of the bluegills?

Ultimately, is it genetics or environment which allows one of our favorite panfish to grow to trophy sizes? Or, could this be like a 7’2” basketball star and his 6’4” track star wife birthing a tall super-athlete?  

Surely there’s enough science out there to give us the truth…and some logical answers to that question. I called Dr. Anderson to make sure I completely understood his question, and to seek his opinion from decades of fisheries work. The octogenarian said he suspects bluegills evolve over decades to adapt to their environments, but he has no idea how much is truly genetic and what part is repetitive conditioning of that particular habitat and environment. In other words, if a bluegill thrives in that particular environment, and select numbers of its offspring does the same, and its offspring has some that thrive, are those traits passed downward, genetically?

The answer is, “No one truly knows”.

I called Eric West, Pond Boss forum moderator and Pond Boss columnist who keeps his brain in as many scientific papers as anyone I’ve ever met. Eric forwarded several informative papers that helped yours truly begin to wrap my brain around this concept a little deeper. I called Bill Cody, from northwestern Ohio, another Pond Boss forum moderator, a microbiologist and knower of things large and small. He didn’t have an answer, other than, “Someone needs to do some genetic work on bluegills and define it for all of us”.

Yep, but that’s another topic.

Cody did lay out a parallel. He described, from one kernel of corn, a plant grows. That plant offers its ears. Each kernel is pollinated from itself or from another plant, but when we shuck that corn and look at the kernels, they are different. Some have a slightly different shape, some have a different color. He suspects there’s a parallel natural variation among bluegills, too.


Speaking of cornhuskers, Dr. Bruce Condello, Pond Boss forum moderator from Lincoln, Nebraska, also offered his thoughts. “For more than seven generations and ten years I hand-selected the best of the best bluegills from my hatchery ponds on a farm I owned. I’d take the top 1% (or less) fish and stock them together. Then, after a few months, I’d take the best of those fish, trying to select the fastest growing bluegills with the best potential to grow to large sizes, and then see if their babies exhibit similar characteristics over time.” He said, “I selected for fast growth, color, and body conformation.”

Did it work?

“After about four generations, I started noticing some recessive genes expressing themselves. There were some traits I didn’t like. By then, I’d learned about populations of fish on feed, so I added some of the best feed-trained fish, and the ensuing generations were showing some different traits that I preferred. I liken it to changing bulls in a herd.”

“My goal was to try to figure out if selective breeding could bring out the best traits, and to see if I could figure out how to breed bluegills to grow fast, and large.”

He found out that genetics are much more complicated than they appear. While many of his bluegills grew well beyond one pound, others seemed to cower, or decline. Offspring from even the best of the best sunfish still grew as proportionately as the average ones. There were fish which thrived and others that were average, and those which just couldn’t make the cut to reach a trophy size.

Science suggests bluegills are resilient enough to be able to adjust to their environments and the quirkiness of a changing aquatic situation. In scientific studies, survival rates and those fish’s ability to thrive were contingent on a variety of circumstances and stimuli. Of course, food is a big key, and oftentimes a variable. Bluegills spawned in early spring don’t have the same food chain that late-spawned bluegills have. If you think about it, the first-spawned fish should have the best advantage. They’ll have new food and a longer growing season to start. But, if we think about it a little more deeply, when those first babies see the light of day, the food chain is just beginning to ramp up and is lacking the volume of natural food a body of water will see as the season progresses. Studies have suggested that late-spawned bluegill grow at a faster rate than those hatched much earlier.

When a pond or lake has a variety of species and size classes of fish, there’s a variation of what to expect from that population of fish. For example, if yellow perch or crappie exist, their babies can eat bluegill babies…at the very least they’ll compete in the food chain. Also keep in mind that bluegills are carnivores, limited by mouth size.

The bottom line is bluegill are resilient species, overcoming what may seem astronomical odds. Some of that resilience is related to genetics, but bluegill’s ability to adapt is amazing as well. A scientific term for their behavior related to genetics is plasticity. That word describes how adaptable a species might be to its environment. Genetically speaking, scientists might be able to test the genetics of a population of huge bluegills in North Carolina and they be exactly the same as a mediocre population of bluegills in central Arkansas…and those fish in Arkansas never reach comparable sizes as those in North Carolina.

Probably the most significant anecdotal story I can share about plasticity revolves around using fish food to grow big bluegills. I started messing with bluegills, literally, around 1980. I really didn’t understand the species. Heck, I’d been out of college for all of a year. But, I’d learned that bluegills were considered the backbone of the food chain for largemouth bass. An old fish farmer shared his knowledge back then. Bus Hartley, from Hartley Fish Farms in Kingman, Kansas, was the only person I could find back then that commercially raised bluegills. He taught me volumes about that species, how to handle, and how to stock them to provide food for bass in a recreational fishing lake. Granted, after those early years, there was much more to learn from other sources, but that was my introduction. Mr. Hartley explained how they were able to grow, grade, and sell bluegill to such nice, uniform sizes, to stock in fishing lakes.

The main thing I’ll always remember from him was to expect bluegills to grow as large as 8-10” in a natural environment. Back then, that was a huge sunfish, but not so big as to turn heads in a bass lake.

Fast forward a couple of decades. By 2004, I’d held maybe 5 bluegills larger than 1½ pounds. I’d held maybe 50 between 1¼ -1½. But, I’d seen or held thousands that weighed between a pound and 1¼. By that time, I could stand in front of a crowd as I gave a pond management speech and tell them they could raise bluegill to a pound, or slightly larger.

In 2005, things changed. Dr. Mark Griffin, who was one of Purina Mills’ nutritionists, began working on a fish meal-based fish food to see if we could change growth rates and eventual sizes via nutrition.

It worked. I’ve now personally seen thousands of bluegills way beyond two pounds, and a handful larger than three pounds in private fishing ponds and lakes.


But, interestingly, not all bluegills which consume that great fish food grow to huge sizes. A percentage of the population adapted and adjusted to the added nutrition.

That’s part of plasticity.

In nature, sans fish food, bluegill have to overcome many odds. First, the egg has to hatch. Not all eggs hatch. Next, the tiny fry can’t catch any of the pathological barriers always in water. If they don’t acquire a fungus, or a bacterial infection, and absorb their yolk sac to become swim up fry, they must avoid being eaten by everything from their parents to insects. Yes, insects will eat tiny fry. If these babies avoid that, they have to be able to find food. Keep in mind, a newly hatched fish has a tiny mouth. A bluegill’s mouth may be one-tenth the size of the head of a pin. Tiny mouths need tiny food. If food’s available, fry can grow to a size you can almost tell by looking at it what it is. Now, it’s about as big as a dime. As days progress, surrounding habitat, food chain, and predator load has a direct impact on what happens to that spawn of fry. Those which are aggressive, sly, evasive…and lucky, are the ones that make it a few weeks into life. Fewer still are the fish resilient enough to overcome other specific sets of odds to make it to adulthood. Even more staggering is to understand the sub-adults and adults have to face ever-changing environmental conditions in order to thrive and survive.

Those factors are huge reasons that bluegills are typically multiple spawners, spawning in pulses during the season. The further south you go, the more spawns that happen. But, that doesn’t mean survival rates will increase, primarily because there’s typically an ever-growing, ebbing and flowing population of largemouth bass or other predator which has an effect on survival and growth rates. When we factor in the environmental and habitat issues bluegills need, it seems overwhelming.

One of the scientific studies revealed bluegills in areas without rooted aquatic plants were as much as 20% longer than bluegills which grew up in reasonable amounts of underwater greenery. That’s plasticity. Those fish able to dart around to find food, mostly zooplankton, were the ones which survived. They adjusted to Nature’s offerings. They were probably longer because they had to expend more energy to go find food and had to eat more to keep up with the energy while their sedentary cousins hanging in dense vegetation didn’t have to go far, and with less risk of being eaten.

Here’s the bottom line. Do you need to consider genetics of bluegills when you stock your favorite fishing hole? That answer is a resounding, “Yes”. Stock fish from local sources. They’ve proven themselves over decades of your specific geography and climate. Will coppernose bluegills survive and thrive along the southern states? That answer is, “Yes”. But, will they do well in Wisconsin? That answer is, “No” …because that strain of fish isn’t adjusted to that climate. Is there a genetic difference between strains? That answer is, “Yes” …but there’s not enough science to prove that there are more than a few strains. As complicated as all that sounds, keep in mind your best choices when it comes to stocking bluegills is to use a strain from hatcheries within your climate zone.

If you start with good fish, some acclimated to your part of the country, the bluegills will do the rest. With great habitat and a fairly predictable climate, along with good husbandry on your part, you can have bluegills and a good number of them will shine, regardless of what their DNA may say.       

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