What's really neat about this is that it swims the way a fish (or perhaps we) swim, not using a propellor but but by flexing its body. And the flexing isn't based on simple mechanical actions (like leg mechanics on a robot). The "muscles" are dielectric elastomers embedded in silicone structures which flex when current is applied, moving the silicone.

Chinese Scientists Engineer Flexible, Faster-Swimming Robot - WSJ