Schematic illustrating the hydrodynamic benefit gained by an individual fish swimming in a two-dimensional
school if a diamond formation is adopted. A reverse von Ka´rma´n street is generated by the propulsive motions of
two individuals, which can be exploited by a downstream individual if positioned between the two preceding
individuals. Side-by-side thrust wakes generated by two individuals in a school create a Ka´rma´n street analogous to that seen behind a bluff body in the flow such as a D-section cylinder Fish can exploit the energy of discrete vortices as well as the average reduced velocity in the Ka´rma´n street. Additional mechanisms are discussed in the text. Blue represents clockwise vorticity and red represents counter-clockwise vorticity.