Tree-climbing Fish Filmed Hopping Along Water Before Jumping Onto Land and Walking Away

A tree-climbing species of fish has been filmed hopping along the water and jumping onto land in a way that has never before been seen.

The unusual method of moving across water was seen in a species of mudskipper. These are amphibious fish that can walk on land and live both in and out of water. They tend to live in tropical and subtropical regions, nesting in burrows in mangroves and mudflats. There are 32 known living species.

The mudskipper in the latest research, Periophthalmus variabilis, was observed for a month in its natural habitats in the Mangkang region, of Central Java, Indonesia. Researchers had previously noticed the species for its ability to climb trees—one of the few fish known to do this—and were trying to learn how it does this.

"We had understood a fair amount about how they stick to the trees and rock faces, but we wanted to know more about how the body parts worked together to enable tree climbing," Parvez Alam, from the U.K.'s University of Edinburgh, told Newsweek.

Alam and colleagues filmed the mudskippers between 10 a.m. and 2 p.m. local time every day. They gently encouraged mudskippers on land to move using a tree branch. With slow motion footage, they were able to track its movements in detail. Findings are published in the journal Zoology.

From their films and to their surprise, they discovered an entirely new method of fish locomotion—using its body to propel itself so it could hop across the water. While doing this, mudskippers reached speeds of about 1.7 meters per second (5.6 feet per second.) Over the course of the study, fish were filmed leaving land to hop across the water, taxiing along the surface of the water, and hopping along the water on to a solid surface.

"This species of fish is an odd one as it likes to spend more time out of water than in it according to our observations," Alam said. "We expected tree climbing, as we had known about this for a few years... We didn't expect it to start hopping across the surface of the water. This was especially bizarre as we'd often see it jump off a vertical incline—like a mangrove root—hop across the water to get away from us, only to then hop off the water back onto a vertical incline."

He said the team has spent time observing several different species of mudskipper, and P. variabilis is the only one they have seen climbing trees and water hopping.

The water hopping appears to be a way of escaping. The footage shows the species can make sharp turns to change its path while hopping. This may suggest they are able to visually navigate, indicating they "possess biologically advanced escape tactics."

Next the team plans to analyze the skin of P. variabilis and compare it to fish species that cannot climb trees or hop across water. They will look at other mudskippers and their methods of traveling. While filming, they noticed other species appeared to have unique ways of traveling along the water surface.

"We also want to better understand the kinematics of climbing, which was the original reason we were there," Alam said, adding that as an engineer, he hopes to mimic the characteristics observed in these mudskippers in robots.

mudskipper
Representative image of a mudskipper on a mud flat. Researchers have found a species that can hop along water in a way never reported before. iStock
Tree-climbing Fish Filmed Hopping Along Water Before Jumping Onto Land and Walking Away | Tech & Science