Locomotion of bluefish

Area of Science:

• Biomechanics
• Comparative Physiology
• Evolutionary Biology

Background:

• Understanding the biomechanics of aquatic locomotion is crucial for insights into evolutionary pathways.
• Fish locomotion involves complex interactions between muscle power, drag forces, and skeletal structure.

Purpose of the Study:

• To quantify the drag forces experienced by a swimming bluefish.
• To measure the propulsive forces and acceleration capabilities of bluefish.
• To assess the structural integrity of the bluefish vertebral column under high acceleration.

Main Methods:

• Profile drag was calculated from body surface pressure measurements, resolved into vectorial components.
• Tangential drag was estimated using a thin plate approximation.
• Thrust and drag were determined from acceleration and deceleration phases during steady swimming.
• Maximal acceleration was measured during a simulated escape response.

Main Results:

• Net drag was calculated to be 0.26 kg at 1.8 m/sec, comprising profile (0.18 kg) and tangential (0.08 kg) drag.
• Calculated drag at 1.1 m/sec was 0.08 kg, consistent with drag varying quadratically with velocity.
• Maximal acceleration reached 3g, requiring a propulsive force of 6.9 kg.
• Vertebral compression strength was approximately 20 kg/cm², providing a safety factor of 3 against maximal acceleration.

Conclusions:

• The bluefish's vertebral column can withstand forces experienced during maximal acceleration.
• The findings suggest that adaptations for terrestrial locomotion might have evolved from aquatic capabilities.
• Fish may possess inherent strengths for overcoming inertia and drag, potentially pre-adapting them for terrestrial movement.