Airacuda

Airacuda is a remote controlled, pneumatically driven fish currently on display at ars electronica:

"The Airacuda moves smoothly and almost noiselessly through the water: In design, shape, and kinetics it follows its biological model.

Electronics and pneumatics are hidden within its waterproof head and control the S-shaped movements of the tail fin via two fluidic muscles. Two further muscles are used for steering.

The fin consists of an alternating traction and pressure edge, which are connected via frames. If an edge is pressurised, the geometrical structure curves automatically against the direction of the influencing force. It sounds complicated, but it is actually a simple principle, with which the fish can display the full swinging power of its fins in the water. This structure is called the Fin Ray Effect."