How Swimming Together Unlocks Superior Efficiency
The synchronized movement of a fish school is one of nature's most mesmerizing spectacles—a living, flowing tapestry that changes direction in perfect harmony. This captivating behavior has long fascinated both casual observers and scientists. While the "safety in numbers" benefit has been well understood, with individuals in large groups having a lower probability of becoming prey, biologists have speculated for decades about another potential advantage: energy conservation.
The idea that fish might save energy by swimming together has proven remarkably difficult to test—until now. Enter Yangfan Zhang, a postdoctoral researcher in Professor George Lauder's lab at Harvard University, whose groundbreaking work is revealing the remarkable energetic benefits of collective movement through innovative experiments that measure both aerobic and anaerobic metabolism in schooling fish 1 .
Zhang's research, featured in the Journal of Experimental Biology Spotlight on Researchers, provides some of the first direct measurements of how fish in schools conserve energy compared to solitary swimmers . His findings help explain why this coordinated group locomotion is so prevalent among fishes and may offer insights for designing more efficient underwater vehicles and swarm robotics. The study represents a significant methodological advancement in the field, overcoming previous limitations by accounting for the full spectrum of energy expenditure during fish locomotion.
First direct measurements of energy conservation in schooling fish using both aerobic and anaerobic metabolic analysis.
Fish in schools use up to 56% less energy per tail beat compared to solitary swimmers.
The theoretical foundation for energy savings in collective movement dates back to seminal work by Weihs in the 1970s, who proposed that fish could gain hydrodynamic benefits by swimming in precise formations 1 . Similar principles apply to other collective movements in nature: birds flying in V-formations, ducklings swimming behind their mothers, and even cyclists in a peloton all potentially exploit fluid dynamics to reduce the cost of locomotion.
In water, which is 50 times more viscous than air and contains much less oxygen per kilogram, the need to reduce fluid dynamic drag is particularly crucial 1 . As swimming speed increases, the energy required to overcome water resistance grows exponentially—fluid drag scales as velocity squared. This relationship makes high-speed swimming especially costly, creating strong selective pressure for mechanisms that conserve energy.
Prior to Zhang's work, evidence for energy savings in fish schools was largely indirect or based on computational models and robotic systems. These studies suggested several potential mechanisms for how fish might save energy when swimming together.
More viscous than air
Timing tail beats to exploit vortices shed by neighboring fish
Positioning themselves in areas of reduced flow created by upstream fish
Taking advantage of the school's collective body to effectively create moving "channel walls" that reduce drag
However, without direct metabolic measurements, these proposed mechanisms remained theoretical, and some studies even suggested that group movement might sometimes increase costs due to the need for constant positional adjustments 1 . The complex interaction between collective behavior and fluid dynamics demanded rigorous experimental investigation.
Zhang and Lauder addressed the challenge of directly measuring energy expenditure in schooling fish through an elegant experimental design featuring the giant danio (Devario aequipinnatus) as a model species. Their approach combined advanced respirometry with detailed kinematic analysis to paint a comprehensive picture of energy use across a wide range of swimming speeds 1 .
The researchers used a specialized swim-tunnel respirometer equipped with two orthogonal high-speed cameras to capture three-dimensional fish kinematics. This "aquatic treadmill" allowed precise control of water velocity while measuring oxygen consumption 1 .
Both solitary fish and schools of five fish were tested across a broad spectrum of water velocities, ranging from near-still conditions (0.3 body lengths per second) to maximum sustained swimming speeds (8.0 body lengths per second) 1 .
The respirometer directly measured oxygen consumption rates to quantify aerobic metabolism. Additionally, the researchers developed methods to account for anaerobic energy contributions, which are particularly important during high-speed swimming but had been largely overlooked in previous studies 1 .
After high-speed swimming trials, the team measured how quickly fish returned to their resting metabolic rates, providing insights into the metabolic perturbation caused by strenuous exercise 1 .
The researchers employed sophisticated analytical approaches to extract maximum metabolic rate estimates from oxygen depletion traces, acknowledging that such methodological choices significantly impact metabolic measurements 2 .
This comprehensive approach allowed the first-ever characterization of the total energy expenditure performance curve for fish schools across the full range of sustainable swimming speeds.
Devario aequipinnatus
Key features:
Zhang's experiments yielded striking evidence of substantial energetic benefits for schooling fish across multiple dimensions of performance. The data revealed not only significant reductions in energy expenditure but also enhanced recovery capabilities that could prove critical for survival in predator-prey interactions.
| Performance Metric | Solitary Fish | Schooling Fish | Improvement |
|---|---|---|---|
| Total Energy Expenditure (per tail beat) | Baseline | Up to 56% reduction | 56% |
| Maximum Sustained Speed Energy Use | Baseline | 53% less | 53% |
| Maximum Aerobic Performance | Baseline | 44% higher | 44% |
| Non-aerobic Energy Used (at high speed) | Baseline | 65% less | 65% |
| Recovery Time (after exercise) | Baseline | 43% faster | 43% |
Less non-aerobic energy used by schooling fish at maximum swimming speed
Faster recovery time for schooling fish after strenuous exercise
The data demonstrated that fish schools have a concave upward shaped metabolism-speed curve, with a minimum metabolic cost occurring at approximately 1 body length per second—coinciding with the typical migratory speed recorded for many fish species in nature 1 . This alignment suggests that fish have evolved to travel long distances at their most efficient speed.
Perhaps even more impressive were the performance advantages observed at high swimming speeds. When reaching their maximum sustained swimming speed, fish in schools used 65% less non-aerobic energy compared to solitary individuals 1 . This non-aerobic (glycolytic) energy savings is particularly significant because the byproducts of anaerobic metabolism can cause metabolic perturbation that requires recovery time—during which fish would be vulnerable to predators. The fact that schooling fish recovered from exercise 43% faster than solitary fish represents a potentially life-saving advantage in natural environments 1 .
| Swimming Speed (body lengths per second) | Solitary Fish Energy Cost | Schooling Fish Energy Cost | Energy Savings |
|---|---|---|---|
| Low Speed (0.5 BL/s) | Baseline | Moderate reduction | ~20-30% |
| Optimal Migratory Speed (1.0 BL/s) | Baseline | Maximum reduction | ~53% |
| High Speed (4-6 BL/s) | Baseline | Substantial reduction | ~45-50% |
The implications of Zhang's findings extend far beyond explaining why fish swim together. The research provides insights into fundamental biological principles of collective movement that operate across vertebrate species, from fish schools to bird flocks. The demonstrated energetic advantages may help explain the evolutionary prevalence of coordinated group locomotion despite the potential costs of increased competition and disease transmission.
From an ecological perspective, these findings enhance our understanding of fish migration patterns and predator-prey dynamics. The reduced recovery time for schooling fish after high-speed swimming could be decisive in survival scenarios where predators initiate multiple attacks. Similarly, the energy savings during routine swimming could allocate more resources to growth and reproduction, potentially increasing lifetime fitness.
The research also holds promise for biomimetic engineering applications. Underwater vehicles designed to operate in coordinated groups could achieve significant energy savings by exploiting similar fluid dynamic principles. The findings might inspire the development of autonomous underwater drones that can maintain formation for extended missions or swarm robotics that collectively conserve battery power through strategic positioning.
Yangfan Zhang's work, featured in the Journal of Experimental Biology, represents a significant advance in our understanding of vertebrate locomotion . By combining rigorous experimental design with innovative metabolic measurements, his research has provided some of the most compelling evidence to date for the energetic benefits of collective movement.
As we look to the future, this research opens up exciting new questions: How do fish precisely coordinate their movements to achieve these energy savings? Can these principles be scaled to much larger marine animals? How might changing ocean conditions affect the energetic advantages of schooling behavior? Whatever the answers, Yangfan Zhang's work has clearly demonstrated that when it comes to swimming efficiently, there is strength—and savings—in numbers.