Simple phalanx pattern leads to energy saving in cohesive fish schooling.

Area of Science:

• Collective animal behavior
• Hydrodynamics
• Fish biomechanics

Background:

• Animal collective movement, such as flocking and schooling, serves various functions like predator evasion and foraging.
• Schooling in fish is often linked to improved energy efficiency, though specific formations and their benefits are debated.

Purpose of the Study:

• To investigate the schooling dynamics and energy efficiency of red nose tetra fish (Hemigrammus bleheri).
• To challenge the conventional notion that fish school in diamond patterns for optimal efficiency.

Main Methods:

• Experiments conducted in a controlled shallow-water tunnel with red nose tetra fish.
• Stereoscopic video recordings used to track 3D positions and tail-beating kinematics of individual fish.
• Analysis of schooling configurations at velocities exceeding typical free-swimming speeds.

Main Results:

• Contrary to expectations, fish adopted a 'phalanx' or 'soldier' formation (side-by-side swimming) at high speeds.
• Tail-beating synchronization between neighboring fish was characterized and found to be a key factor.
• Schooling was demonstrated to be more energy-efficient than solitary swimming.

Conclusions:

• The phalanx formation, facilitated by synchronized swimming, is advantageous for energy efficiency in red nose tetra fish, especially at higher speeds.
• This finding challenges established models of fish schooling patterns.
• Collective schooling behavior provides a significant energetic advantage compared to individual swimming.