from the article

The researchers designed their bio-inspired robotic fish to mimic the tail propulsion of a swimming fish, and conducted experiments at varying tail beat frequencies and flow speeds. In nature, fish positioned at the front of a school beat their tails with greater frequency, creating a wake in which their followers gather. The followers display a notably slower frequency of tail movement, leading researchers to believe that the followers are enjoying a hydrodynamic advantage from the leaders’ efforts.

In an attempt to create a robotic leader, Marras and Porfiri placed their robot in a water tunnel with a golden shiner school. First, they allowed the robot to remain still, and unsurprisingly, the “dummy” fish attracted little attention. When the robot simulated the familiar tail movement of a leader fish, however, members of the school assumed the behavior patterns they exhibit in the wild, slowing their tails and following the robotic leader.