Owing to the rotation of the vortices in a reverse Ka´rma´n street , downstream flow outside the wake will be slower than the jet of water through the centreline of the wake. A fivefold energy saving is predicted for the Weihs’ model, given the condition of a two-dimensional school constrained to a single horizontal plane. The lateral proximity of neighbours in a
school, if less than one body length apart, can increase an individual’s swimming performance through wall or channelling effects. Similarly, the proximity of the school to the substrate can potentially lead to ground effects. These mechanisms can theoretically increase the thrust of an individual by tens of percentages without additional energy expenditure.