Fish Gotta Swim — But only George Lauder can tell us how

George Lauder hits a few keys on his laptop, and a moving image appears on the screen.

“That’s the fish’s pectoral fin,” he says, pointing to the grainy, black-and white-picture. “It’s slowed down because the camera was taking 250 images per second. But do you see the way the water is moving in a sort of loop behind it?”

The pattern is hard to see at first because even at 250 frames per second, the movement seems to happen in the blink of an eye. The only thing that makes it visible at all is the fact that the bluegill sunfish in Lauder’s experiment is swimming through water that is awash with tiny silvery glass beads that catch the light and reveal the fluid’s movement.

Lauder, whose appointment as professor of organismic and evolutionary biology in the Faculty of Arts and Sciences began this past September, is in the midst of conducting what may be the most thorough and technologically sophisticated study to date of how fish swim. It is a study that applies techniques borrowed from engineering to visualize the flow of water around the fish’s body.

Both this study and Lauder’s earlier work have impressed colleagues as important contributions to the field of organismic and evolutionary biology.

“I am thrilled to have George join our Department and very much look forward to teaching with him,” said Professor of Biology Andrew Biewener. “George is an outstanding evolutionary and functional morphologist who has been a leader in the areas of feeding and more recently the locomotion of fishes. His work has been ground-breaking, both for its insight into functional mechanisms as well as for placing the evolution of those mechanisms into a phylogenetic context. His appointment greatly strengthens our programs in vertebrate biology. It will be a real pleasure having George as a colleague in this enterprise.”

Karel Liem, the Henry Bryant Bigelow Professor of Ichthyology and Curator of Ichthyolog y, said that Lauder “is looked upon as the world’s foremost researcher of the form, function, and evolution of vertebrates.”

Liem, who has known Lauder since he was a sophomore at Harvard and supervised his Ph.D. dissertation, said that his former student was “a superb experimentalist, but also a very accomplished theoretician. What makes him exceptional is that he has been able to interpret his findings within an evolutionary perspective, which is what makes the theoretical implications of his work so important.”

Liem added that Lauder was also an extremely effective teacher on the undergraduate, graduate, and postdoctoral levels.

The slow-motion movie of a fish swimming through glass bead-filled water that Lauder demonstrates on his laptop records one of many experiments he did while at the University of California, Irvine. He is now setting up the same apparatus at Harvard and expects to be up and running in another month or two.

The central piece of equipment is a flow tank, a continuous Plexiglas loop about 6 feet long, completely filled with water. An electric propeller at one end keeps the water circulating around the loop.

A fish, inserted into the middle of the loop, instinctively swims against the current to maintain its position in the water. Meanwhile, a laser, shining from below, can be adjusted to illuminate one of the fish’s fins, allowing Lauder to photograph the movement with a video camera.

Also, thanks to the glass beads suspended in the water, the camera also captures the fluid dynamics produced by the fin’s interaction with the water. This information is entered into a computer, which calculates the matrix of velocities of the fluid in the wake of the fish’s fin.

What these experiments reveal is that the fin doesn’t simply push the water backward as one might expect. Instead, it produces something called “an obliquely oriented toroidal vortex ring.” In layman’s terms, the moving water describes a donut shape, with each point in the flow traveling in a loop before shooting through the hole in the donut.

“These vortex rings were predicted by physicists,” Lauder says, but we’re the first ones to accurately measure the forces involved.”

Overcoming the technical obstacles and accurately graphing such an obscure and fleeting phenomenon seems a worthy accomplishment in itself. But for Lauder, it is only the beginning of a much more ambitious project.

“I’m using fish as a model to investigate an issue that has concerned biologists since Darwin’s time, namely the evolution of physiological and biomechanical function in an organism. In other words, if we see an animal as a very complex machine, the question is, how do these complicated mechanisms evolve? How do the transformations occur? What are the rules?”

To answer these questions, Lauder has been repeating his flow tank experiments with a variety of fishes, from primitive species like sharks to those further up the evolutionary ladder like paddlefish and sturgeon, to the more advanced teleost fishes, a large category which includes trout, bass, carp, tuna, mackerel, and many others.

“Continuing this comparison across the evolutionary range of fishes will tell me something about the diversification of their locomotor machinery,” says Lauder.

Through these experiments, Lauder hopes to understand how fish evolved the ability to swim and how the physical mechanisms that made this activity possible changed and diversified over time.

One hypothesis he plans to test derives from his earlier studies of fish skulls.

In most fish, the skull is a complex arrangement of hundreds of independently moveable bones controlled by hundreds of muscles. This arrangement is in stark contrast with most mammalian skulls, in which the bones are tightly linked together without much possibility of movement.

Lauder has found that the structural fr eedom that characterizes the fish skull is associated with great evolutionary diversity. It is possible that the key to how fish evolved their ability to swim may be traced to a similar principle.

“It may be that when you increase the number of independently moveable parts, it permits greater flexibility. You can put things together in a greater number of different ways.”

The son of a State Department official, Lauder, 45, grew up in several different areas of the world. It was while living in Beirut, Lebanon, that he developed an interest in the aquatic environment. He pursued that interest as a Harvard undergraduate, earning his bachelor’s degree in biology summa cum laude in 1976. He earned his master’s and doctoral degrees in 1978 and 1979, respectively, then spent two years as a junior fellow in the Society of Fellows. He taught at the University of Chicago before joining the faculty at the University of California, Irvine.

A prolific author, Lauder has published more than 120 scientific articles and book chapters. His research has received continuous support from the National Science Foundation since 1981.

Lauder’s energy is evident in his recreational pursuits as well as in his scholarly work. He enjoys rock climbing and trail running and participates in an annual spring run across the Grand Canyon, 24 miles from rim to rim!