Chinese scientists have developed a minuscule, non-motorized soft robotic fish powered by an artificial muscle.

Scientists from Zhejiang University said their robotic fish can swim at a fast rate of speed despite not having an electric motor by bending or stretching itself.

The robot is only 9.3 centimeters long and weighs a scant 90 grams. It consists of an electric controller; fins made of silicone and a silicone body and tail. All components are transparent except for a small lithium battery pack and two electromagnets.

Instead of being driven by traditional rigid motors, the fish relies on its artificial muscle for underwater propulsion. The artificial muscle is made out of stimuli-responsive polymers that bend or stretch under a cyclic voltage generated by the embedded lithium battery.

A muscle in the body makes the fish bend and straighten, causing the fins to flap like those of a manta ray to move the robot through the water. When a voltage was applied to it, the robot fish swam at a speed of 6.4 centimeters per second, or 0.69 body lengths per second, which is double the speed of previous soft robot swimmers.

The robot carries its own onboard system for power and remote control, and was able to swim for three hours on a single battery charge.

With a tethered exterior power supply, the fish can swim up to 14 centimeters per second, or about the same speed as similar-sized fish.

"Soft artificial muscle can respond quickly to electricity, meaning faster fin flapping and greater speed," said Li Tiefeng, an associate professor at Zhejiang University.

"The soft and transparent body will make it easy for the robot to sneak through narrow reefs without being damaged or detected by other sea creatures."

Li expects the robot to be used to record the temperature and salinity of the sea and detect pollutants.

"The materials used in the robot are common, cheap and environment friendly, with the potential to be produced on a large scale in China," said Li. "Our next step is to improve the efficiency of the artificial muscle and develop key techniques for mass production."

The findings were published in the academic journal, Scientific Advances.