Summary:

Researchers built a robotic Indian leaf fish, which is a natural predator of the zebrafish, and found zebrafish are less likely to swim away if they have been exposed to ethanol.

Zebrafish
photo: Princeton

Fish, like humans, can have complex relationships with robots. Researchers found last month that zebrafish take a liking to robots that look like zebrafish. Now, they’ve discovered that robots that resemble a predator inspire fear in zebrafish — unless they’ve been hitting the bottle.

Researchers are keen to show animals respond similarly to robots and their fellow animals — friends and enemies alike — because robots are much more suited to scientific studies. Robots are fully controllable, reproduce tests accurately and are never influenced by the test subjects. They could also make entirely new types of tests possible.

Researchers from the Polytechnic Institute of New York University and Instituto Superiore di Sanità in Rome, Italy, built a robotic fish that moved and had markings similar to the Indian leaf fish, which preys on zebrafish in the wild. Then they dropped the robot and a zebrafish into separate, but connected, compartments in a three section tank. The zebrafish showed a strong preference for swimming into the empty third compartment, as opposed to the compartment that contained the robot.

Robotic fish and heron

That changed when the researchers introduced alcohol. Booze is a useful tool for researchers because it provides evidence an animal is acting out of anxiety.

They added ethanol to the tank until the water contained a 0.25, 0.5 or 1 percent concentration. The zebrafish regularly avoided the robot until the concentration hit 1 percent, at which point they were roughly as likely to swim away or toward the robot. They were also less likely to swim or thrash — two evasive maneuvers — and more likely to freeze in place.

The drunk fish also failed other evasive tests. Zebrafish were placed in a tank with two compartments. One side was well lit, while the other was dark. Sober fish spent 70 percent of their time in the light part of the tank, while fish exposed to the 1 percent ethanol concentration spent about 55 percent of their time there. When the researchers simulated an attack with a fake heron, the drunk fish were still more likely than the sober fish to swim into the dark side of the tank. They also responded to the attack more slowly.

“We hoped to see a correlation between the robotic Indian leaf fish test results and the results of the other anxiety tests, and the data support that,” study coauthor Maurizio Porfiri said in a release. . “The majority of control group fish avoided the robotic predator, preferred the light compartment and sought shelter quickly after the heron attack. Among ethanol-exposed fish, there were many more who were unaffected by the robotic predator, preferred the dark compartment and were slow to swim to shelter when attacked.”

As any nervous college freshman will tell you, alcohol is known to dampen one’s fears. So when the drunk zebrafish suddenly avoided the robot less, the researchers were more confident the sober fish swam away due to anxiety upon recognizing a predator: robot or not.

“These results are further evidence that robots may represent an exciting new approach in evaluating and understanding emotional responses and behavior,” Porfiri said.

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