The model is skinned and fully rigged for realistic animation. Rig has intuitive and animator friendly controls.
There is a parametric wave 'inside' animation rig. Every body control have an attribute called 'follow wave': 0 - do not follow wave, 1- follow wave. And you can animate rotation of this controls as well. With such setup it is very easy to animate complex swim animations. Please take a look at promotional files to see animation that comes with model and animation rig in action.
Contact me if you have any questions or need a new motion.