New Study Reveals Fish Swim in 3D Ladder Patterns, Not Diamonds

In a groundbreaking study published in the journal *Scientific Reports* on June 28, 2025, researchers from Princeton University and Harvard University have redefined our understanding of fish schooling behavior. For decades, scientists believed that fish conserved energy by swimming in flat diamond formations, a concept rooted in earlier models by Weihs and Lighthill in the 1970s. However, the new findings indicate that fish predominantly adopt a dynamic, three-dimensional 'ladder' formation when swimming in schools.

This research involved tracking six giant danios over a continuous ten-hour period within a recirculating flow tank. Using synchronized side and bottom cameras along with advanced deep learning software, the team collected over 260,000 frames to analyze the fish's spatial arrangements. Contrary to previous assumptions, only 0.1% of the observed frames recorded the fish in the classical diamond formation, while a staggering 79% of pairings exhibited the ladder structure. This suggests a significant oversight in earlier studies, which primarily focused on two-dimensional swimming patterns.

According to Dr. Hungtang Ko, lead author of the study and a researcher at Princeton University, the ladder formation allows fish to reduce drag while maintaining proximity to their peers. 'When swimming, fish generate a jet stream moving backward, similar to a jet engine,' Dr. Ko explained. 'By swimming slightly above or below one another, fish can avoid this jet, resulting in energy savings without the need for precise alignment.' This insight not only challenges the traditional view of schooling behavior but also highlights the variability in coordination among fish, as they rarely beat their tails in sync, a requirement for the diamond pattern to be effective.

The research team also noted that the average position of fish changed every 48 seconds for individuals and every 32 seconds for the entire school, showcasing a high degree of adaptability in their swimming patterns. These findings were made possible by using deeper tanks and steady flow conditions, contrasting with previous studies that used shallow tanks, leading to unnatural formations.

The implications of this study extend beyond biology. The Nagpal lab, which collaborates with the researchers, is exploring how these findings can inform the design of robotic fish swarms. By mimicking the ladder formation, these underwater robots could potentially conserve energy and improve navigation for tasks such as reef monitoring. Dr. Ko emphasized the reciprocal nature of this collaboration: 'We can use computer vision to understand animal group behavior, and then apply those insights to real-world robotic systems.'

As researchers continue to explore the complexities of fish swimming patterns, new questions arise regarding the adaptability of robotic fish in varying conditions. Will these machines be able to shift positions while maintaining energy efficiency? How effective are vertical ladders in turbulent waters? Future experiments, particularly those involving robotic models, may yield answers to these queries.

This study not only revolutionizes the understanding of fish schooling behavior but also underscores nature's preference for complexity over perfect symmetry. As researchers delve deeper into these behaviors, it becomes clear that fish do not swim in flat diamonds; instead, they navigate their environments by climbing invisible ladders, one body length at a time.