Watching fish swim

Jan 07, 2014 by Julie Flaherty
Eric Tytell with his lampreys. Credit: Alonso Nichols

As fish go, the lamprey has to be one of the most repulsive. Its eel-like body culminates in a tooth-encrusted sucker mouth straight out of a sci-fi horror film. Yet it turns out the lamprey, the most primitive of vertebrates, can do a pretty neat trick: bounce back from paralysis.

"Clip the , stick them back in the water, come back in a couple of weeks or so, and they will often be swimming pretty much indistinguishably from how they did before," says Eric Tytell, an assistant professor in the Department of Biology in the School of Arts and Sciences.

The lamprey does repair the break to some extent, but the neurons that connect across the breach are shorter and make fewer, smaller synapses than before. And that, to Tytell, is the more interesting part, because it means that it is not just the connection to the brain that is important for swimming, but something going on in the spinal cord itself.

The cord "isn't a simple cable," Tytell says, explaining that it does a lot of processing in its own right. In fact, neural circuits in the spinal cord, so-called central pattern generators, are what control locomotion. "In fish, that's swimming—in you and me, that's walking," Tytell says. "It's the same structure of the circuit, as far as we can tell." Understanding how lampreys relearn to swim could help in designing better therapies for people who have .

The spinal cord work is just a small piece of the research Tytell conducts by doing what many people do only in their dentist's waiting room: watching fish swim. He does it to answer the fundamental question of how fish manage to "move stably through complex environments." He has observed knifefish moving in and out of tubes, scared the bejeezus out of African bichir fish to test their escape reflex, and done seminal work on the fluid dynamics of the American eel. But you can learn other things from fish gazing, such as best practices in underwater propulsion.

The U.S. Navy is always in the market for quieter, more efficient submarines, particularly ones that are nimble enough to get into near-shore areas and search for mines. "It's debatable whether a fish is better than a propeller for long-distance swimming," Tytell says. "It's certainly not debatable that a fish is more maneuverable." Some of his past experiments have included tuning a submersible's rubber fins to undulate like those of a fish.

Tytell is also interested in the ecological aspects of how fish deal with their environments, such as how a bluegill sunfish might react when a well-meaning alternative power company installs a hydrokinetic turbine in its stream. "Clearly these are going to introduce turbulence into the water, and we really don't know how well fish deal with those vortices," he says.

To study things like that, he uses a crystal-clear Plexiglas tank with a constant current for a fish to swim against. When reflective powder is sprinkled in the tank, and a laser is directed in it, a high-speed camera catches the vortices and flows the fish creates as it bends its body and flaps its fins. These flows push back on the fish, creating a complex dance of fluid mechanics and biomechanics.

"There are internal forces and external forces, and the balance of the two is what determines how a fish moves," says Tytell, who has studied both physics and biology and whose bookcase reflects his blend of disciplines, with titles such as Worlds of Flow and Animals in Motion.

The equations involved are so complex that only recently have computers been powerful enough to allow Tytell, while a postdoctoral researcher at the University of Maryland, to develop a robust computer simulation of a swimming . This lets him tweak variables such as body stiffness to see how they affect speed or acceleration. It is a model for how a moving body interacts with its surroundings, and something that could one day be used in the creation of robotics and prosthetics. "An awful lot of prosthetics out there right now are entirely passive or have pretty limited ability to adapt to any sort of changes in the environment—going uphill versus going downhill, for instance," he says. "So if we understand a bit better how changing sensory information can change the actual pattern of locomotion, that could help with prosthetic design."

In the meantime, he is gearing up for an experiment on beheaded lampreys. (If you feel bad, think of it as cosmetic surgery.) "You can actually remove the brain entirely, and if you stimulate the circuits in the spinal cord with a drug or electrically, they will swim, they will respond to perturbations, they will do quite a bit of fairly sophisticated stuff," Tytell says.

He points out that in humans, the central processing generator for walking is located in the lumbar spinal cord. "If you can simply activate and then control it at least a little bit—turn left, turn right—then maybe rather than trying to design some fancy exoskeleton, we could take advantage of what is already there. That is very much in the early days, but it is a possibility."

Explore further: Study sheds light on nerve regeneration following spinal cord injury

add to favorites email to friend print save as pdf

Related Stories

Fish offer clues to spinal cord renewal

Apr 06, 2011

(PhysOrg.com) -- Spinal cord injuries are devastating, but fish may be the key to finding a cure.Research shows adult fish that sustain a spinal cord injury have the miraculous ability to not only regenerate ...

Fish study raises hope for spinal injury repair

May 30, 2012

(Medical Xpress) -- Scientists have unlocked the secrets of the zebra fish’s ability to heal its spinal cord after injury, in research that could deliver therapy for paraplegics and quadriplegics in the ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 0

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.