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Researchers have described how fish larvae rely on species-specific combinations of vision and movement to detect and capture prey.

The study is in eLife as the Version of Record after previously appearing as a Reviewed Preprint. Editors highlight its state-of-the-art quantitative methods to characterize and compare behaviors across five different fish species to understand which hunting behaviors are conserved and which have diverged over evolutionary time. The results are deemed convincing, with potential interest to ethologists and researchers studying the neural basis of behavior.

Zebrafish larvae are widely used as a model system for investigating the neural mechanisms of behavior, including prey capture. However, it is unclear whether the complement and sequence of movements used by zebrafish while hunting is universal across other species of teleosts—the large and diverse group of ray-finned fish that make up over 95% of all living fish species. Many of these species share similar ecological pressures, but may have evolved different solutions for detecting, tracking and striking at prey.

"Zebrafish are a powerful model of fish behavior, but they're just one point on a much larger evolutionary map," says co-lead author Duncan Mearns, at the time of the study a postdoctoral researcher at the Max Planck Institute for Biological Intelligence, Department Genes—Circuits—Behavior, in Martinsried, Germany, and now at the Princeton Neuroscience Institute, Princeton, US.

"We were interested in whether the strategies we see in zebrafish are general features of larval fish behavior, or whether different species tackle the problem of hunting in different ways."

To explore their question, the team compared the prey-capture behavior of zebrafish with five other species of teleosts—including four African cichlids and the Japanese rice fish, medaka—which diverged from the zebrafish's lineage around 240 million years ago.

"We used high-speed cameras and deep-learning-based tracking tools to record and analyze thousands of hunting episodes from individual fish larvae placed in controlled environments with live prey," explains co-lead author Sydney Hunt, at the time of the study a Master's student in the Graduate School of Systemic Neurosciences, Ludwig Maximilian University of Munich, Germany, and now a Ph.D. student at the Max Planck Institute of Animal Behavior, Radolfzell, Germany.

"This allowed us to map tail movement, eye position, and prey location during every step of prey pursuit and capture."

Their analysis revealed distinct strategies among the species. All four cichlid species shared the same general binocular hunting strategy as zebrafish, converging their eyes to bring prey into the center of their field of view before striking. In contrast, the medaka relied on monocular tracking, swimming continuously and striking from the side without converging their eyes.

This suggests that cichlids and zebrafish rely on binocular disparity to judge distance, while medaka may instead use motion parallax—a depth cue based on the prey's position relative to the hunter as it moves through space.

The researchers also found clear differences in how larvae swam during hunting. Cichlids paused intermittently, which likely aided binocular depth perception, whereas medaka glided smoothly past their prey in continuous motion. The team also analyzed tail movements in a shared low-dimensional "pose space" using principal component analysis. This revealed that cichlids employ a more varied set of swimming "syllables" than seen in zebrafish in previous studies, including unique behaviors such as tail coiling, hovering, and backward swimming after a failed strike.

Across the cichlids, two main types of capture strikes were observed: an "attack swim" involving symmetrical tail movements, and a more explosive "capture spring" preceded by tail coiling. Medaka, by contrast, used a single, lateral "side swing" strike. Even among the closely related cichlids, the number and variety of behaviors differed significantly, pointing to a species-specific specialization in motor control.

"Our findings challenge the assumption that zebrafish behavior is a universal model for fish larvae," concludes senior author Herwig Baier, Director and Scientific Member at the Max Planck Institute for Biological Intelligence and head of the Department Genes—Circuits—Behavior.

"Different species rely on different sensory inputs and motor strategies, even at very early developmental stages. By understanding these variations, we can begin to better interpret how brain circuits support behavior, and how evolution shapes those circuits in different lineages."