Challenging zebrafish escape responses by increasing water viscosity

Area of Science:

• * Biomechanics and Locomotion
• * Hydrodynamics and Fluid Mechanics
• * Animal Behavior and Physiology

Background:

• * Fish escape responses are a model for studying maximal muscle power output and rapid body bending.
• * The fluid mechanical environment's effect on locomotor kinematics is not fully understood.
• * Previous studies have not extensively explored the role of fluid viscosity in escape behaviors.

Purpose of the Study:

• * To investigate the effects of altered water viscosity on the kinematics of zebrafish escape responses.
• * To differentiate the impact of viscosity on acceleration-dependent versus velocity-dependent hydrodynamic forces.
• * To test hypotheses regarding the differential effects of viscosity on early (stage 1) versus later (stage 2) escape phases.

Main Methods:

• * Zebrafish (Danio rerio) escape responses were analyzed using high-speed video at 1000 frames s(-1).
• * Kinematics were compared across three media with varying viscosities: 1 mPa s (normal water), 10 mPa s, and 20 mPa s.
• * Key kinematic variables including displacement, velocity, acceleration, and timing were quantified.

Main Results:

• * Increased water viscosity significantly affected escape response kinematics, but not as predicted.
• * Higher viscosity decreased center of mass displacement, maximum velocity, angular velocity, and acceleration during stage 1.
• * Increased viscosity lengthened the time to maximum angular and linear velocity, yet did not significantly alter stage durations.

Conclusions:

• * Altered fluid viscosity significantly impacts the mechanics of zebrafish escape responses.
• * The observed kinematic changes suggest complex interactions between viscosity and hydrodynamic forces.
• * Despite significant kinematic alterations, the overall duration of escape stages remained largely unaffected by viscosity changes.