From boundary layer to behavior: Chemical orientation in the brown bullhead (Amieurus nebulosus)

Chemical signals are critical for the survival of many organisms, which must examine the environment in order to gather the appropriate information. How the environment is sampled depends upon the sensory appendages of the organism and the distribution of the signal in the natural environment. Flow speed, boundary layer and body morphology can affect the spatio-temporal information in chemical signals. These factors and sampling behavior were examined in the brown bullhead, an ideal organism for studies on chemosensory abilities. The first study examined the distribution of the chemical signal along the body of a model brown bullhead. Several signal parameters were analyzed to ascertain the characteristics of the chemical signal. The second study examined the chemosampling behavior of the maxillary barbels. The last study examined the role of hydrodynamics on the orientation ability of the brown bullhead. Differences in signal parameters were found along the body and at different flows. Results of the first study illustrated that the presence of the model, flow speed and point position on the model affects the chemical signal properties and thus influences the type of information the bullhead can perceive. The second study indicated that the barbels spatially sample the environment by fully extending themselves. This behavior would allow fish to sample a larger odor field during food search. The last study illustrated that brown bullheads are more successful in the flow environment that they are adapted to and their swimming behavior is different under different flow conditions. The overall results of this study indicate that chemical orientation in brown bullheads involves a complex interaction between physical forces and behavioral responses. In order to truly understand chemical orientation in organisms, both behavioral displays of the organism and the physical aspects of the environment must be examined.