Although we have seen robotic fish designed to unobtrusively study marine life, scientists more often use rigid remote-operated vehicles with noisy propellers that scare animals. That could eventually change, however, thanks to the development of a totally silent, transparent, soft-bodied robotic eel.

Inspired by transparent eel larvae, the robot measures about a foot long (0.3 m) and was designed by scientists from the University of California San Diego, and the University of California Berkeley. It's made for use in salt water, and is powered not by a motor, but instead by water-filled elastomer artificial muscles.

Supplied with electricity via cables running up to a surface-located electronics unit, the robot delivers positive electrical charges to the water pockets in its muscles, plus it delivers negative charges into the water immediately surrounding it (the charges carry little current, so shouldn't harm marine organisms). This causes the muscles to bend back and forth, allowing the robot to undulate forward through the water at a rate of 1.9 mm per second.

It's already been successfully tested at UC San Diego's Scripps Institution of Oceanography, in tanks containing jelly fish, coral and fish. The scientists now plan on improving its geometry and reliability, and giving it a functional ballast system. Down the road, it could be equipped with a head containing sensors such as cameras.

"Our biggest breakthrough was the idea of using the environment as part of our design," says UC San Diego's Prof. Michael T. Tolley, corresponding author of a paper on the project. "There will be more steps to creating an efficient, practical, untethered eel robot, but at this point we have proven that it is possible."

The paper was recently published in the journal Science Robotics. To see the robot in action (with its muscles filled with fluorescent dye), check out the following video.

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