This robot fish is just 10 centimeters in length. It uses an extremely low power means of locomotion and is powered by a solid-polymer fuel cell called a "power tube". It was developed by the Faculty of Engineering at Osaka City University
(Little Robotic Fish Has Solid-Polymer Fuel Cell)
If you have a neodynium magnet inside a coil with about 3,000 turns, and pass a current through the coil, the magnet moves sideways. When we used this effect to drive the robot's tail, power consumption was just 10 milliwatts.
In his 2002 story Slow Life, science fiction author Michael Swanwick writes about robot fish who help explore distant worlds:
The Mitsubishi turbot wriggled, as if alive. With one fluid motion, it surged forward, plunged, and was gone.
Lizzie switched over to the fishcam.
Black liquid flashed past the turbot’s infrared eyes.
Straight away from the shore it swam, seeing nothing but flecks of paraffin, ice, and other suspended particulates...
(Read more about the Mitsubishi turbofish)