Here is another robotic fish designed to allow researchers to study aquatic life closely. MIT’s Computer Science and Artificial Intelligence Laboratory developed SoFi to swim alongside real fish. This soft robot can dive up or down or swim in straight lines. Specific moves can be made with a waterproofed Super Nintendo controller.
The robot swims by undulating its tail and controlling its own buoyancy. A Linux PC is embedded in its head. More info is available here.