Researchers have developed a fish-like robot that shows how some species of modern fish are able to walk on land, and could help unravel how early vertebrates evolved similar abilities hundreds of millions of years ago.
Using a combination of their ‘walking fish’ robot and computer models based on observations of real fish, the researchers, led by the University of Cambridge, found that a wide range of unrelated species have independently evolved the same basic walking gait, which essentially mimics a swimming motion on land.
This simple walking pattern, which the researchers call an ‘undulating tripod gait’, looks flopping and clumsy, but is actually one of life’s most ancient solutions to a problem: how to escape predators or move from one habitat to another, without specialised limbs.
The gait is mechanically simple – fish propel themselves forward with their tails while using their front fins or head for support – and re-emerges in unrelated fish species, from the African lungfish to armoured catfish. Although individual species of walking fish are well-studied, this is the first time that unifying locomotive principles across multiple species have been identified.
This plausible example of convergent evolution – where different species evolve similar abilities independently – could also help researchers understand how vertebrates first made the transition from water to land, one of the most significant events in the history of life on Earth. The results are reported in the journal Nature Communications .
Several species of living fish, including bichirs, lungfish, catfish, sculpin and snakeheads, are capable of walking on land. While they are far more efficient in the water, having an extra mode of locomotion they can use when needed is an evolutionary benefit.
“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 lead author Dr Michael Ishida, from Cambridge’s Department of Engineering. “You’ve also got the ability to move from one shallow-water environment to another, like tide pools for example.”
Ishida, an engineer in Professor Fumiya Iida’s lab at Cambridge, worked together with biologists and palaeontologists to study how modern fish walk, and whether those results could be used to help determine how ancient fish made the transition from water to land.
The researchers first created a computer model based on the movements of Polypterus senegalus , a grey bichir native to Africa, and several other walking fish. The model found similar modes of locomotion across several different species.
“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.”
Ishida and his colleagues called this walking motion an undulating tripod gait: the fish anchors its body with the front fins or head, and uses its tail to push the body forward around that anchor point.
“It looks like a swimming fish dumped onto land,” said Ishida. “A swimming fish uses its body to propel itself through the water, so if you take that, put it on land, give it some ability to shuffle its front fins, that’s exactly what it’s doing.”
The researchers then built a physical robot fish to test their results, and found that the most efficient movement closely matched the bichir’s movements and the results from the computer model.
“We tried all kinds of different gaits on the robot, and every other gait we tried was slower,” said Ishida. “Any time we changed how the body bended, or what sequence it was bended 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 researchers say that future work in this area could be applied to fossil fish like Tiktaalik , an important fossil link in the transition from water to land. A similar combination of computer modelling and robotics could help determine how these ancient species first walked on land.
Nature Communications
The undulating tripod gait as a model of the locomotion of walking fish
2-Jun-2026