Meeting Abstract

78.2  Sunday, Jan. 6  Will spit for food: role of target height in the spitting force of hunting archer fish. BURNETTE, MF*; ASHLEY-ROSS, MA; Wake Forest University; Wake Forest University burnmf0@wfu.edu

Archer fishes (Toxotidae) are famous for their method of hunting terrestrial insects: the fish fires a stream of water from its mouth, which will dislodge a potential prey item from a leaf or branch overhead. Archer fish in the lab are known to shoot as far as one meter and wild archer fish are expected to encounter terrestrial prey at many different heights. It is known from previous studies that firing the stream of water is energetically costly and that tuning the shot accordingly will help keep these costs to a minimum. It is also known that archer fish tune the stream of water to prey size, such that larger prey are hit with shots that have more kinetic energy. To do this, the fish tunes the mass of the fired shot, but not its velocity. However, it is not known how target height influences shot force. If the fish fired a shot that was not tuned to height, a low target may be hit with more force than necessary to dislodge it, while a target further away might not be hit hard enough. The goal of the present investigation is to determine how the force of an archer fish’s shot varies with target height. Using a paper cricket silhouette as a target and a force transducer, we measured the force of the shot on the target at four different heights (0.2 to 0.8 meters elevation, in 0.2 meter increments). Our results suggest that targets presented closer to the water surface are hit with more force while targets further away are hit with less force. High-speed video of the stream of water shows that velocity remains consistent, even between shots fired at targets that differ in height, but the shape of the shot changes with target height. At lower elevations, the shot appears more stream-like in its shape, while at high elevations, the shot breaks up into smaller droplets that strike the target.