Mathematical modeling and analysis of biological systems such as swimming and flying is an interdisciplinary research field with an extensive range of applications including the design of unmanned underwater robots and swarm of robots that swim together in a coordinated way similar to schooling fish. One of the main objectives of our work is to develop mathematical models for certain aspect of schooling. In particular, we examine (1) the interaction of a single fish with ambient vorticity possibly generated by other neighboring fish; and (2) the interaction of multiple fish wakes in large fish schools.; For the first part, we propose a reduced model of a rigid body interacting with point vortices in potential fluid and demonstrate that the rigid body can swim upstream in the direction opposite to the motion of point vortices at no energy cost. Indeed, the rigid body itself does not generate any force and its motion is due entirely to the energy exploited from the presence of the point vortices. We comment on the stability of these motions and propose under-actuated active control methods to achieve locomotion in unsteady wakes.; In the second part, we consider the interaction of multiple reverse von K´arm´an vortex streets as a model of the mid-wake region of large fish schools. We focus on the wake dynamics to gain insight into the role of the fluid in transporting oxygen and nutrients to inner fish as well as its role in facilitating or acting as flow barriers to passive locomotion.; We examine the topology of the streamline patterns in a frame moving with the same translational velocity as the streets which lends insight into fluid transport through the mid-wake region.