‘Nightmare’ robofish spooks virility out of tail-eating mosquitofish

Image credit: Dreamstime

A team of biologists and engineers from Australia, the US and Italy have developed a robotic fish that mimics the natural predator of mosquitofish, prompting a fear response of weight loss, changes in body shape and reduction in fertility in the latter.

The invasive mosquitofish (Gambusia holbrooki) is a pest, chewing the tails from freshwater fish and tadpoles and leaving these native animals to perish while feasting on other creatures’ eggs. Aiming to frighten away this aquatic bully, researchers set about engineering a robot inspired by the appearance and movement of the mosquitofish’s natural predator, the largemouth bass (Micropterus salmoides).

“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,” said Giovanni Polverino of the University of Western Australia, first author of the iScience study.

“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.”

Robotic fish with mosquitofish

Mosquitofish with 'worst nightmare' robotic fish/Giovanni Polverino

Image credit: Giovanni Polverino

Aided by computer vision, the robotic fish 'strikes' on spotting mosquitofish approaching a species of Australian tadpole (Litoria moorei) threatened by mosquitofish in the wild. Scared and stressed, the mosquitofish showed fearful behaviours, experiencing weight loss, changes in physiology and a reduction in fertility. All these changes impair their survival and reproduction.

In the presence of the robotic fish, mosquitofish were observed remaining close to each other and spending more time at the centre of the testing arena, hesitant to adventure into uncharted waters. They also swam more frenetically – with frequent and sharp turns – than those who were yet to encounter the robot. Even when the mosquitofish returned to their home aquaria, the biologists noted that the effect of fear lasted; the scared fish were less active, ate more and froze longer, exhibiting signs of anxiety that continued weeks after their last encounter with the robotic fish.

The tadpoles, on whose tails the mosquitofish usually preyed, benefitted from the presence of the robotic fish. While the mosquitofish is a visual animal that surveys the environment mainly using its eyes, tadpoles have poor eyesight.

“We expected the robot to have neutral effects on the tadpoles, but that wasn’t the case,” said Polverino. As the robot changed the behaviour of the mosquitofish, the tadpoles thrived in the absence of predators and gained the confidence to adventure further out into the testing arena. “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.”

After five weeks of face-offs between mosquitofish and robotic fish, the researchers found that the mosquitofish were allocating more energy towards escaping than reproducing. The male fish’s bodies became thin and streamlined, but with stronger muscles near the tail for fleeing. The males also had lower sperm counts, while females produced lighter eggs; these changes are likely to compromise the survival of the invasive population.

“While successful at thwarting mosquitofish, the lab-grown robotic fish is not ready to be released into the wild,” says Maurizio Porfiri of New York University, senior author of the study. The researchers next plan to test their robotic fish in small, clear pools in Australia, where two endangered fish are threatened by the mosquitofish.

“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.”

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