“…Nevertheless, among numerous mathematical articles studying fish locomotion, most of them address the case of a potential flow which is by definition vortex-free like in the works of Kelly and Murray [14], Kozlov and Onishchenko [15], Kanso, Marsden, Rowley and Melli-Huber [13], Melli, Rowley and Rufat [22] and Munnier [26]. It is also the point of view we have chosen in what follows and on which we focus from now on.…”