One field in which nature outperforms current technology is fish swimming, because its efficiency, manoeuvrability and noise are far better than those of typical ship propellers. These advantages are not only due to the streamlined shape and the low-drag skin, but also and above all to the propulsion mechanism, which makes thrust generation possible with small energy dissipation in vortices. Nowadays the interest in autonomous underwater vehicles is in constant increase following the emerging needs of underwater mining and fish farming. Batoid fishes produce thrust with their pectoral fins, they essentially produce a wave travelling in the direction opposite to their motion, pushing water backwards and gaining thrust as a consequence of momentum conservation. The motion of the fin has been studied and reproduced with a series of articulated mechanisms. In this work the optimization of the mechanism’s geometry is described and the experimental results on the reconstructed fin are presented. Moreover, a bioinspired robot mimicking cownose ray locomotion has been designed and built. In this paper the functioning of this robot is shown.