Fish Fear Robotic Predators, Unless They're Drunk

Scientists swear they had a really good reason for building a robotic fish, getting some other fish drunk, and then chasing them around with it.

The robotic bird head, too.

Researchers at the Polytechnic Institute of New York University and the Istituto Superiore di Sanità in Rome were interested in zebrafish. These thumb-sized, striped fish are laboratory favorites because their genome is well understood, they reproduce quickly, and their embryos are totally transparent.

One area of research that employs zebrafish is the study of emotions, including anxiety and fear. Outside of a lab, people may not spend much time pondering fish anxiety. But study coauthor Simone Macrì of the Istituto Superiore di Sanità says zebrafish can help unravel complex environmental and genetic interactions, such as emotion, because their genetics are not a mystery. Their simple brains are useful for "clarifying some fundamental aspects [of] emotions," he says.

It's easy to spook a little fish; all you have to do is show it a predator. But wrangling live predatory animals such as birds or other fish is inconvenient. It also adds an unwanted variable to an experiment, since your predator may not behave consistently (or may have moods of its own). So Macrì and his colleagues wondered if they could build robotic predators good enough to be stand-ins in these experiments.

They carefully crafted robots that looked like a natural zebrafish enemy, the Indian leaf fish. ("The visual appearance of the robotic fish was obtained by spray-painting the robot with an ivory base color followed by the hand painting of brown color patterns typical for this species," the authors write—in case this is a project you want to try at home—"as well as the attachment of small plastic eyes.") A motor let the robot fish wave their tails at various speeds. There was also a robotic heron head that plunged toward the water as if hunting.

To find out whether their robots made the same impression on zebrafish as a real predator, the researchers let the animals meet each other. Sure enough, zebrafish swam to the far side of their tank when a robotic leaf fish was in the water. When a robotic heron struck from above, zebrafish darted under a shelter.

Then, to make sure the fish were responding to the robots out of fear or anxiety, the researchers gave the zebrafish a drug that reduces anxiety: alcohol. After letting their subjects swim around in ethanol-spiked water, the researchers gave them the same tests. Now they didn't flee the robot fish and were slow to seek shelter after the robotic heron attack.

As the researchers had hoped, sober fish feared robotic predators, and alcohol lessened those fears. The results are published in PLOS ONE.

Macrì thinks this technique could help researchers who study anxiety with zebrafish improve their methods. As long as scientists are looking at simple behaviors, he says, "the robots are ideally suited." And after being chased by a giant robotic predator, zebrafish might need a drink anyway.


Images: left by Azul, via Wikimedia Commons; right Cianca et al. (In reality, the robotic fish were several times larger than the zebrafish.)

Valentina Cianca, Tiziana Bartolini, Maurizio Porfiri, & Simone Macrì (2013). A Robotics-Based Behavioral Paradigm to Measure Anxiety-Related Responses in Zebrafish PLOS ONE DOI: 10.1371/journal.pone.0069661