The robotic prototype swimming under water propelled by fins, it was developed at the Control Systems and Robotics Laboratory of the Technological Educational Institute of Crete, in Heraklion (Greece) and it’s controlled by an Arduino Mega:

Each fin is comprised of three individually actuated fin rays, which are interconnected by an elastic membrane. An on-board microcontroller generates the rays’ motion pattern that result in the fins’ undulations, through which propulsion is obtained. The prototype, which is fully untethered and energetically autonomous, also integrates an IMU/AHRS unit for navigation purposes, a wireless communication module, and an on-board video camera. The video contains footage from experiments conducted in a laboratory test tank to investigate closed loop motion control strategies, as well as footage from sea trials.

the Arduino runs a custom-developed real time firmware that implements two Central Pattern Generator (CPG) networks to generate the undulatory motion profile for the robot’s fins. The robot  contains a  7.4V lipo battery powering also a Bluetooth module for wireless communication and a video camera to record footage of the missions.