Robot Inspired by Walking Fish Could Reveal How Animals First Moved Onto Land

In the swamps of Southeast Asia, changing temperatures can cause water sources to dry up entirely for periods of the year. For many fish that call these environments home, this is a major problem. But for the walking catfish (Clarias batrachus), drought is only a minor inconvenience.

That’s because this fish can breathe out of water for up to 18 hours.

Using a distinctive wiggling walk, the catfish simply ditches its dried-out home and migrates to other aquatic spots. This ability isn’t unique. Bichirs, lungfish, snakeheads, and sculpins are all fish that can walk on land, too.

Now, a new study has created a robot that mimics the walking pattern of the walking catfish and several other fish that survive on land. The authors hope the findings could even help explain how our ancient ancestors first left the oceans and began walking on land. The research was published in Nature Communications.

Designing a Fish Out of Water

mechanical boxes intersecting to maneuver like a fish out of water — A fish-like robot used in the study
(Image Credit: Michael Ishida)

To design their robots, the team studied the gait of walking fish, which makes them look as if they are trying to swim on land.

The researchers called this motion an "undulating tripod gait,” and it involves the fish propelling themselves forward with their tails while supporting themselves with their front fins or their heads. Individual walking fish have been studied, but this new research was the first to connect the movement principles they all share.

“If you’ve got the ability to walk on land and your predator doesn’t, then you can escape, and hopefully the predator moves on,” said Michael Ishida, who studies bio-inspired robots at the University of Cambridge and who co-authored the study, in a statement. “You’ve also got the ability to move from one shallow-water environment to another, like tide pools, for example.”

Why Understanding Walking Fish Is Important to Evolution

The researchers wanted to understand whether the way fish alive today walk on land could help them understand how ancient fish first transitioned onto land.

First, the team created a computer model based on another walking fish, the grey bichir (Polypterus senegalus). They realized the bichir’s movement method was highly similar to that of other walking fish.

“We kept seeing this recurring kind of walking motion, although it’s very primitive,” said Ishida. “A number of different fish, spread out across the evolutionary tree and not closely related to each other, all do it. It’s such a simple movement and can recur from a very basic starting point.”

Next, the team built a robot that recreated the walking fish’s movements. The most efficient movement strategy that the robot could adopt closely resembled the bichir’s flop-walk.

“Every other gait we tried was slower,” said Ishida. “Any time we changed how the body [bent], or what sequence it was [bent] in, it was worse. It was surprising that the optimal walking pattern in the simulation and robot matched what the real fish actually do.”

The team now hopes that a similar approach, combining computer modeling and robots, could help explain how ancient fish, like Tiktaalik, first began walking. A Tiktaalik fossil found in Arctic Canada dates back 375 million years. Understanding how these ancient fish moved from sea to land would answer a major question about early life on Earth.

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article: