A Funny Fish Feeding Finding: Largemouth Bass Eat with Their Backs

When a largemouth bass spies a tiny, edible fish, he opens his mouth wide and sucks his prey into gaping jaws. You’d think that the fish’s mouth would be the most important part of creating that powerful suction, right? Nope. It’s their back muscles that power their feeding. In a study published this summer in the Proceedings of the National Academy of Sciences, a team of researchers used the most sophisticated tools out there to reveal exactly how exactly largemouth bass feed. The study, edited by the University of Chicago Associate Dean for Academic Strategy Neil Shubin, PhD, was accompanied by a commentary by professor of organismal biology (and avid fisherman) Mark Westneat, PhD, professor of organismal biology and anatomy. ScienceLife sat down with Westneat to discuss this fishy finding.

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Mark Westneat, PhD, professor of organismal biology and anatomy

ScienceLife: So fish eat with their backs? Really?

Mark Westneat: Yes, around 95% of the power for suction feeding actually comes from the back muscles.

How does that work and how did we not know about it before?

MW: We’ve been studying suction feeding for decades and we have been putting together this amazing picture of how this explosive event is powered. The back muscles power the suction feeding, and the swimming muscles along the body are co-opted to help. We knew that but we didn’t know the extent to which the swimming muscles were powering everything. The main source of power emanates from the back muscles located behind the head which yank up the fish’s head. The axial muscles, the big white parts of the fish that we like to eat, are active two-thirds of the way down the body and we know from other studies that they are used for fast acceleration. What the researchers at Brown did to describe this phenomenon in such detail was to use a state-of-the-art three-dimensional imaging system.

What was it about the imaging system that allowed them to make these insights?

MW: The team at Brown produced an impressive piece of work that combined muscle modeling and three-dimensional CT scanning to build the 3-D fish that you see in the videos. Specifically, they used a technology called X-ray Reconstruction of Moving Morphology, or XROMM. The analysis works by tracking little beads that have been put in the fishes head. By following the beads, researchers can determine the precise patterns of motion that are happening inside of the fish’s head with slow motion cameras and high-speed x-ray.

That’s the big advantage, the combination of high tech imaging, anatomical reconstruction, with the X-ray that reconstructs the motion really accurately.

Do you think you’ll use any of the techniques or conclusions from the paper to spur forward your own work?

MW: The exciting thing about XROMM is that, while the group who wrote this paper pioneered it at Brown University, we just bought it here to Chicago. There’s a group of us in the anatomy department who wrote an NSF grant that got funded last year. We have XROMM on campus now. It’s just been set up within the past couple of months.

What will the XROMM enable researchers here at the University of Chicago to study?

MW: While it is fairly specialized, a lot of different research projects can be done with XROMM. Researchers who study the biomechanics of fish feeding, frog jumping and primate chewing will find it valuable. Biomechanics is the study of how living things work. For example, how do the tendons and contracting muscles in your arm allow your fingers to type on a computer? It’s an interesting problem in anatomy, physics and physiology and it’s all about how these parts move together.

So can you use the XROMM to study human biomechanics?

MW: While you can’t stick a human in there, you can non-invasively look at jaw muscle function, reaching and grasping in model organisms, like primates. The cameras attached to the X-ray are high-speed cameras; you can take about 500 video frames per second of X-ray video. So when you’re doing something like snapping your fingers, you can get all the different stages of behavior in X-ray. Which is pretty cool.

How were you selected to write a commentary on the Camp et al paper?

MW: My research actually focuses on fish biomechanics and feeding. Neil Shubin is an editing member from PNAS and when he received the Camp et al paper, he suggested to the editor that one of his colleagues might be interested in writing a perspective commentary piece on it. So he gave it to me to review.

Were you excited about putting together the commentary?

MW: I jumped at the chance because I work on feeding in fishes and I’m also an avid fisherman. I actually grew up in Ohio fishing for largemouth bass, which is part of the reason why I do what I do. While I’m mostly marine fish now, I still love freshwater fish.

Westneat (@mwestneat) via Twitter: “The appropriately named Gafftopsail Catfish, Bagre marines. #Everglades #SICB2015 #CatchAndRelease “

From a fisherman’s perspective, do you think any of the discoveries made in this paper would change the way you would fish for largemouth bass?

MW: Probably not. I wrote the intro to that commentary as a fisherman. You cast your lure out by the lily pads, see a big whirlpool suck your lure down and that’s part of the excitement of fishing. But no, I don’t think this very intense scientific exploration of how the bass head works is necessarily going to change the way we fish or change the way lures are made They make lures for fisherman not for fish. I’ve got about a hundred lures and probably any of them would work.

Even so, do you think fisherman will be interested in this article?

MW: It’s interesting from a behavioral, evolutionary and ecological point of view, and it is interesting to the millions of people worldwide who like to fish. It’s just a little bit deeper understanding of how that whole system works. A lot of fisherman are interested in understanding more about how fish feed, what they eat how they eat it why they eat it. I think the science is focused on this kind of crux moment.  It’s a crucial moment for the predator, the bass, trying to suck in and capture a prey item and it’s critical for the prey, too. This work is really high tech in explaining part of that story.

About Hannah Brechka (5 Articles)
Hannah Brechka is a fourth year graduate student at the University of Chicago, and she studies prostate cancer in Dr. Vander Griend's lab. She's interested in how developmental mechanisms go awry in cancer cells. She's also an avid baker and enjoys brewing her own beer.
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