Lateral Line Behavior
Parmly faculty members are conducting studies on how Lake Michigan mottled sculpin use their lateral line system in detecting water motion created by the small vertebrate and invertebrate prey that they feed on. Mottled sculpin are benthic fish that normally feed at night, when vision is severely restricted. In the lab, blinded sculpin will respond to the vibrations of a nearby, chemically inert object, such as a small vibrating sphere, with an initial orientation towards the source, followed by a stepwise approach to the source. When the source is less than a few cm away, sculpin strike at the source as if it were food. Pharmacological or mechanical blocking of the lateral line system results in a complete disappearance of the orientation and subsequent approach and strike behavior, indicating that the lateral line system is extremely important in helping these fish locate nearby vibratory sources.
Current experiments are designed to measure the ability of fish to localize a nearby, low frequency dipole source, or sinusoidally vibrating sphere. These experiments take advantage of the naturally-occurring feeding response of the mottled sculpin, which is used as a behavioral indicator of how well the fish can determine the location of the source. Localization abilities are measured by videotaping the pathway followed by the fish as it moves towards the source and subsequently analyzing the position of the fish at each step in the pathway relative to the source and its flow field. Since sculpin approach the source in discrete steps, each step can be captured as a frozen video frame and the position of the fish relative to the source can be specified in cartesian coordinates. These coordinates can then be entered into a Matlab computer program that uses the flowfield equations for a dipole source to model the expected flow pattern along the fish and the spatially-distributed lateral line system. Recent research in this area has suggested that sculpin find sources by keeping the source slightly to one side and thus, maximizing information in the spatial pattern of excitation along the lateral line system (Coombs & Conley 1995; Conley & Coombs 1996). In addition to these experiments, graduate students in the Biology Department are conducting similar studies on the ability of muskie, a highly visual predator, to localize live minnow as its prey. Studies on both sculpin and muskie involve selective elimination of the lateral line and visual systems to partition out the role of the lateral line system in feeding and prey localization.