jellyfish ( aurelia aurita ) were obtained from the new england aquarium and maintained in 20-l aquaria at 20 c . for recording
, individual animals were placed into a glass filming vessel ( 30  10  25 cm ) filled with filtered seawater .
recordings of free - swimming animals were acquired by a high - speed digital video camera ( fastcam 1024 pci ; photron ) at 1,000 frames per second .
detailed swimming kinematics ( 2d ) were obtained using imagej v1.46 software ( national institutes of health ) to track the x and y coordinates of the apex of the jellyfish bell margin over time .
bell margin speed was calculated from the change in the position of the margin tip over time as :  
 u=((x2x1)2+((y2y1)2))1/2t2t1 
  jellyfish were illuminated with a laser sheet ( 680 nm , 2w continuous wave ; lavision ) oriented perpendicular to the camera s optical axis to provide a distinctive body outline for image analysis and to ensure the animal remained in - plane , which ensures the accuracy of 2d estimates of position and velocity .
fluid motion created by the jellyfish while swimming was quantified using 2d digital particle image velocimetry ( dpiv ) . using the setup described in gemmell et al .
the velocities of particles illuminated in the laser sheet were determined from sequential images analyzed using a cross correlation algorithm ( lavision software ) .
image pairs were analyzed with shifting , overlapping interrogation windows of a decreasing size of 64  64 pixels to 32  32 pixels .
 the ability of animals to propel themselves efficiently through a fluid medium is ecologically advantageous . 
 flexible components that influence vortex interactions are widespread among animal propulsors . however the mechanisms by which vortices are enhanced and appropriately positioned for thrust generation are still poorly understood . here , we describe how kinematic propulsor movements of a jellyfish can enhance and reposition a vortex ring that allows the recapture of wake energy for secondary thrust generation and efficient locomotion . 
 we use high - speed video and digital particle image velocimetry ( dpiv ) to resolve kinematics simultaneously with fluid structures . 
 these results provide new insight into how animals can manipulate fluid structures to reduce metabolic energy demands of swimming muscles and may have implications in bio - inspired design . 
Materials and Methods