Fish switch leaders 2.8 times a second to stay in sync, reveals a virtual reality study

Schooling fish switched the neighbor guiding their movements about 2.8 times a second in a virtual reality experiment, offering new insight into how they stay in sync.

To investigate coordinated movements in fish, researchers chose the rummy-nose tetras (Hemigrammus rhodostomus) for the study, a species known for its schooling behavior.

Using a closed-loop virtual reality system, real tetras interacted with digital fish that the researchers could control. The projector cast these images of virtual fish on the walls of a 52.2-centimeter bowl containing 15 liters of water. A depth camera tracked the real fish’s movement in three dimensions.

“Collective motion in animal groups emerges from local interactions, yet how individuals select and integrate social information remains poorly understood,” the researchers said.

Investigating schooling behavior

Researchers programmed virtual fish to respond to their one, two, or four most influential neighbors. They conducted eight one-hour experiments for each setup.

The team compared swimming speeds, distances between individuals, alignment, spatial organization, and turning behavior.

They found that coordination increased when the virtual fish responded to more neighbors, the researchers stated in the study.

“Groups became more cohesive, fish trajectories became smoother, and departures of the real fish from the virtual subgroup became less frequent.”

Although the virtual schools became more cohesive when the programmed fish responded to more neighbors, however analyses showed the real fish behaved as if it primarily tracked a single influential neighbor.

“The turning statistics provide a clear behavioral indicator that the dynamics of the real fish are best explained when it responds to a single most influential neighbor.”

And this neighbor wasn’t always the closest fish either.

Influential neighbors switch as they swim

The most influential neighbor changed as the fish moved in sync. Researchers recorded an average switching frequency of about 2.8 times per second.

Roughly 40 changes occurred between two consecutive spontaneous U-turns.

“…Influential-neighbor switching reflects the continuous spatial reorganization of the group rather than periods of sustained leadership by particular individuals.”

Fish coordinate their movements through changing interactions rather than relying on one leader.

“Social influence is continuously redistributed as individuals move relative to one another, generating a rapidly evolving interaction network that nevertheless supports robust collective coordination,” the researchers said*.*

Unlike the previous perspective, coordination doesn’t necessarily require integrating information from many neighbors simultaneously.

Limitations of virtual reality

The researchers acknowledged limitations in their experimental approach.

Although the virtual fishresponded visually to the movements of the real fish, they did not generate water movements or pressure disturbances.

Researchers explained that fish are known to rely on multiple sensory pathways, such as vision, hydrodynamic cues, and pressure sensing through the lateral line system when coordinating their movements within schools.

However, in the virtual-reality set up, the digital fish could only be perceived visually because they don’t generate water movements and pressure disturbances, which would need to be addressed in later experiments.

In the future, the team would like to conduct their experiment on larger groups with the missing conditions built into the model. The results suggest the fish coordinated through continuously changing interactions rather than following a fixed leader.

The research findings were published in PRX Life.

Source: https://interestingengineering.com/science/fish-switch-leaders-2-8-times-second-stay-sync