Scientists have developed a soft robotic fish that they can control with sound to swim beside real fish in the ocean.
The fish – named SoFi – was made from silicon rubber by researchers at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL).
It swims by wagging its hydraulic-pump powered tail and controls its own buoyancy using special foam which allows it to dive or rise to the surface.
SoFi, which was supported by the US National Science Foundation, was developed to be dexterous enough to swim beneath corals and has a camera allowing the researchers to see what is right in front of it.
The electronics that control it are stored inside its head, although a remote controller is also available to allow a diver to control the fish underwater using ultrasonic signals.
According to MIT, during test dives in the Rainbow Reef in Fiji, the robot fish "swam at depths of more than 50 feet for up to 40 minutes at once, nimbly handling currents and taking high-resolution photos and videos using a fish-eye lens."
CSAIL PhD candidate Robert Katzschmann, lead author of a report on the tests, said: "To our knowledge, this is the first robotic fish that can swim untethered in three dimensions for extended periods of time.
"We are excited about the possibility of being able to use a system like this to get closer to marine life than humans can get on their own."
Mr Katzschmann said that SoFi was developed to be as non-disruptive as possible to its environment, producing minimal noise from the motor through to the ultrasonic emissions of its communications system.
"The robot is capable of close observations and interactions with marine life and appears to not be disturbing to real fish," said CSAIL director Daniela Rus.
SoFi is part of CSAIL's work into robots which could be safer than hard-bodied machines which are being developed elsewhere.
Soft robots also alleviate worries over collisions.
"Collision avoidance often leads to inefficient motion, since the robot has to settle for a collision-free trajectory," said Professor Rus.
"In contrast, a soft robot is not just more likely to survive a collision, but could use it as information to inform a more efficient motion plan next time around."
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"We view SoFi as a first step toward developing almost an underwater observatory of sorts.
"It has the potential to be a new type of tool for ocean exploration and to open up new avenues for uncovering the mysteries of marine life."