Fish Follow Robot Impostor

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It's a robot in fish's clothing.

A group of researchers from the Polytechnic Institute of New York University and the Istituto Superiore di Sanita in Rome showed for the first time that a robotic zebrafish attracts living fish, casing them to gather around it and shoal.

It may be possible to use similar robots in the future with other kinds of fish, to draw away pest species or save endangered ones by leading them out of danger. The results are being published in the journal Bioinspiration and Biomimetics.

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Marizio Porfiri, who led the work, has loked at fish behavior in response to robots before. In February he built a robotic fish that generated a wake like a living one, attracting others into a school.

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This latest robotic fish is about six inches long and painted to look like a zebrafish, with a mechanical tail that mimicks the motions of the real deal.

Besides being bigger than a real one (zebrafish are about half that size), the mechanical fish was given a rounded shape so that it looked like a pregnant female, which zebrafish of both sexes prefer to be around.

The researchers used a tank separated into three sections. In the middle section they put the living zebrafish, sometimes in shoals of 10 and other times as singletons. In the outside sections, the researchers experimented with 16 different combinations of using the robotic fish or live fish as a way of getting the attention of the fish in the middle section. Sometimes, they tried nothing at all.

They found that while zebrafish prefer to move towards other zebrafish, the robot fish also stimulated the fish to move towards it. This was true of both shoals of fish and singletons. In addition, the movement of the robot is important; fish were less attracted to a robot that was still. Tests were also run in the dark to see if the stimulus was non-visual. (It wasn't).

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One possible explanation for the approach to the robot fish — which after all is much larger than its real counterparts — is a behavior called "predator inspection" in which a few fish go out to check if another animal is dangerous. The paper discounts that possibility because that behavior declines in captive fish.

Besides insight into designing autonomous robots, the work also gives insight into how fish engage in social behavior and what the cues are.

Image: Institute of Physics