Meeting Abstract

18.5  Jan. 5  It�s all in the timing: forces exerted on prey during suction feeding in Bluegill HOLZMAN, R*; DAY, SW; HIGHAM, TE; WAINWRIGHT, PC; Univ. of California, Davis; Rochester Institute of Technology; Univ. of California, Davis; Univ. of California, Davis raholzman@ucdavis.edu

Suction feeding is perhaps the most common prey capture strategy of fishes. During suction feeding, the predator opens its mouth and rapidly expands its buccal cavity, generating a flow field external to the mouth. The rapid expansion of the buccal cavity produces high fluid velocities and accelerations that persist only a short distance from the mouth (about half of one mouth diameter), and for a short time (a few ms). Therefore, the predator must carefully time its strike to maximize the forces exerted on its prey. Enhancement of the forces can be achieved by increasing water velocities and acceleration, but also through locating the prey closer to the mouth at the time of peak flow speed. The objectives of this study were to directly measure the forces exerted by Bluegill on their prey and to assess the ways in which the fish modified that force. Bluegill were allowed to feed on ghost shrimps tethered to a load cell that recorded force at 5000 Hz, with concurrent 500 Hz video of the feeding sequences. The fish exerted forces on their 23 mm prey ranging from 0.3-0.73 N. In accordance with the short duration of the strikes (time to peak gape of 6-10 ms), the forces recorded were brief and abrupt (5-11 ms from initiation to peak force). Force magnitude fell steeply after the time of peak force. A model incorporating drag, pressure, and acceleration reaction on the prey was used to test the effects of strike initiation distance on peak force and on the rate of increasing force. Comparisons of model output to empirical results indicated that Bluegill had an uncanny ability to time the strike so as to exert 97% of the peak possible force on the prey.