A team of researchers has designed a robot that scares away the invasive mosquitofish, which bites off the tails of freshwater fish and tadpoles to eat their eggs. The new study demonstrates how fear can alter the behavior, physiology, and fertility of the mosquitofish, and it can have big implications in the fight against invasive species.
The study was published on December 16 in the journal iScience.
Drawing Inspiration from Natural Predator
The international team consists of biologists and engineers from Australia, the United States, and Italy. They looked at the largemouth bass, which is the moquitofish’s natural predator, in order to draw inspiration for the new robots.
The team designed a robotic fish that mimics the appearance and simulates the movements of the largemouth bass. With the help of computer vision, the robot can strike when it identifies a mosquito fish approaching tadpoles. The invasive species then demonstrates fearful behaviors and stress before experiencing weight loss, changes in body shape, and a reduction in fertility.
Giovanni Polverino is from the University of Western Australia and first author of the research.
“Mosquitofish is one of the 100 world's worst invasive species, and current methods to eradicate it are too expensive and time-consuming to effectively contrast its spread,” says first Polverino. “This global pest is a serious threat to many aquatic animals. Instead of killing them one by one, we're presenting an approach that can inform better strategies to control this global pest. We made their worst nightmare become real: a robot that scares the mosquitofish but not the other animals around it.”
When the mosquitofish were in the presence of the robotic fish, the former stayed closer to each other and opted to stay in the center of the testing arena. They were fearful of going into uncharted waters. They also swam with more frequent and sharp turns compared to those not encountered by the robot.
Fear That Lasts
When the invasive species finally made it away from the robot, they continued to demonstrate fear. They were less active, consumed more food, and froze longer, demonstrating signs of anxiety for weeks after their last encounter with the robot.
The robotic fish also improved the outlook for the tadpoles that the mosquitofish target. The invasive species is a visual animal, surveying the environment through its eyes, while the tadpoles have poor eyesight and struggle to see the robot.
“We expected the robot to have neutral effects on the tadpoles, but this wasn’t the case,” Polverino says.
Since the robots affected the behavior of the mosquitofish, the tadpoles were more willing to go outside the testing area.
“It turned out to be a positive thing for tadpoles. Once freed from the danger of having mosquitofish around, they were not scared anymore. They’re happy,” Polverino continued.
After five weeks of experiments, the researchers found that the fish allocated more energy towards escaping than reproducing. The bodies of the male fish became thinner, and their tails became stronger to swim away faster.
Maurizo Porfiri of New York University is senior author of the research.
“While successful at thwarting mosquitofish, the lab-grown robotic fish is not ready to be released into the wild,” Porfiri says.
The team will now look to overcome technical challenges and test the method on small, clear pools in Australia.
“Invasive species are a huge problem worldwide and are the second cause for the loss of biodiversity,” says Polverino. “Hopefully, our approach of using robotics to reveal the weaknesses of an incredibly successful pest will open the door to improve our biocontrol practices and combat invasive species. We are very excited about this.”