![]() Specifically, we believe that fish induced to perform escape responses in water of substantially higher viscosity than normal should have to increase muscle power output to accomplish normal kinematics in a similar time frame. One approach that might reveal new features of fish escape response dynamics involves challenging fish to perform their escape behavior under increased loading, i.e. Escape responses by fishes are characterized by large body angular accelerations and displacements ( Domenici and Blake, 1997) and are usually divided into two stages: an initial C-bend (stage 1) and a contralateral bend followed by one or more tailbeats (stage 2). Escape behavior usually occurs in response to an impulsive hydrodynamic or visual stimulus and is usually (though not always) mediated by the Mauthner cells of the hindbrain ( Zottoli, 1977). Borazjani et al., 2012 Frith and Blake, 1995 Tytell and Lauder, 2008). Eaton et al., 1977 Foreman and Eaton, 1993 Liu and Fetcho, 1999), understand rapid activation of axial muscles ( Jayne and Lauder, 1993 Rome et al., 1988 Tytell and Lauder, 2002 Westneat et al., 1998), clarify predator-avoidance dynamics ( Walker et al., 2005) and investigate unsteady locomotor hydrodynamics (e.g. The escape response of fishes is a widespread model of vertebrate locomotor behavior that has been used to clarify the design of neural circuits (e.g. Remarkably, increasing water viscosity 20 times did not significantly affect the duration of stage 1 or stage 2. Statistical tests showed that increasing viscosity significantly decreased displacement of the center of mass during stage 1 and after 30 ms, and decreased maximum velocity of the center of mass, maximum angular velocity and acceleration during stage 1, but increased time to maximum angular acceleration and time to maximum linear velocity of the center of mass. ![]() Our results showed a significant overall effect of viscosity on escape response kinematics but the effect was not in accordance with our predictions. ![]() Similarly, we hypothesized that the kinematics of stage 1 will be less affected by viscosity than those of stage 2, as higher angular velocities are reached during stage 1 resulting in higher Reynolds numbers. We hypothesized that because viscosity is increased but not density there will be a different effect on kinematic variables resulting from unsteady (acceleration-dependent) hydrodynamic forces and steady (velocity-dependent) ones. We quantified escape kinematics using 1000 frames s –1 high-speed video, and compared escape response kinematics of fish in three media that differed in viscosity: 1 mPa s (normal water), 10 mPa s and 20 mPa s (20 times normal water viscosity). In this paper we present the results of experiments that challenged zebrafish ( Danio rerio) to perform escape responses in water of altered viscosity, to better understand the effects that the fluid mechanical environment exerts on kinematics. Escape responses of fishes have long been studied as a model locomotor behavior in which hypothesized maximal or near-maximal muscle power output is used to generate rapid body bending. ![]()
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