This is a realistic 3D model fully rigged, following a path, ready to be animated.
The shark has already a built in system that makes the shark swim along the path, without need to tweak the bones. You can activate or deactivate this system, also animate the bones as you want with this system on, making a very realistic shark behaviour simulation.

You can find fully tutorial here: https://www.youtube.com/watch?v=l24PUYeyFpU