Drag coefficient estimates from coasting bluegill sunfish Lepomis macrochirus

Area of Science:

• * Fluid dynamics
• * Fish biomechanics
• * Aquatic locomotion

Background:

• * Understanding fish swimming requires knowledge of drag forces.
• * Previous drag measurements often used static or 'dead drag' methods.
• * Coasting deceleration offers a dynamic approach to estimate drag in live organisms.

Purpose of the Study:

• * To estimate the drag coefficient of the bluegill sunfish (Lepomis macrochirus) during coasting deceleration.
• * To compare coasting drag with previously reported dead drag values.
• * To explore the implications of coasting drag for fish propulsion efficiency.

Main Methods:

• * Drag coefficient estimation using coasting deceleration in bluegill sunfish.
• * Measurements conducted at a Reynolds number of approximately 41,000.
• * Comparison with existing literature data for dead drag measurements.

Main Results:

• * The drag coefficient was estimated at 0.0154 ± 0.0070.
• * This value falls within the typical coasting drag range observed in other aquatic species.
• * Coasting drag was found to be lower than dead drag measurements for bluegill sunfish and other species.

Conclusions:

• * Low momentum losses during coasting suggest efficient energy use in bluegill sunfish.
• * Coasting drag dynamics may be relevant for understanding intermittent propulsion strategies.
• * Findings highlight the importance of dynamic measurements for accurate biomechanical assessments in aquatic locomotion.