Why stay in school? For fish, the reasons haven't been clear. On the plus side: protection from predators, conserving energy and finding mates. On the down side, though, is the competition for food.

To tease out an answer, Maurizio Porfiri, an engineer at the Polytechnic Institute of New York University, and Stefano Marras, of the Institute for Coastal Marine Environment in Italy, designed and built a robotic fish that generates a wake behind it that's similar to a real fish.

They put the robotic fish in a tank with real fish to see what would happen. The real fish followed the robo-fish around. Later, they attached the robo-fish to the bottom of a channel full of moving water (to simulate a current) and they found the living fish swimming along by the robotic fish, just as though it were leading a school.

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