A hydrodynamic sensory antenna used by killifish for nocturnal hunting

The perception of sensory stimuli by an animal requires several steps commencing with the capture of stimulus energy by an antenna that, as the interface between the physical world and the nervous system, modifies the stimulus in ways that enhance the animal's perception. In view of the morphological diversity of the lateral-line system across species and its accessibility to observation and experimental intervention, we investigated the role of antennal structures on the response characteristics of the lateral line. The surface-feeding killifish Aplocheilus lineatus is able to hunt in darkness by detecting surface capillary waves with the lateral-line system atop its head. This cephalic lateral line consists of a stereotyped array of 18 mechanosensitive neuromasts bordered by fleshy ridges. By recording microphonic potentials, we found that each neuromast has a unique receptive field defined by its sensitivity to stimulation of the water's surface. The ridges help determine these receptive fields by altering the flow of water over each neuromast. Modification of the hydrodynamic environment by the addition of a supplemental ridge changes the pattern of water movement, perturbs the receptive fields of adjacent neuromasts, and impairs the fish's localization ability. Our electrophysiological, hydrodynamic, and behavioral evidence indicates that the ridges constitute a hydrodynamic antenna for the cephalic lateral line.

The spatial sensitivity of individual neuromasts was determined by recording microphonic potentials while 150 Hz waves were generated at different positions along an arc around the head. Each neuromast has a unique receptive field, here portrayed as a red antenna function centered on the fish's head. For comparison, the blue arc depicts the magnitude of the capillary waves reaching the head as a function of their angle of origin and the brown circle represents a cosine function. The specific neuromasts are designated by the side of the animal—here "L" for the left—by group "I," "II," or "III" from rostral to caudal, and by "1," "2," or "3" within each group. 0° is straight ahead, positive angles lie to the left of the fish, and negative angles occur to its right.