Perception of Surface Waves by the Blackstripe Topminnow, Fundulus notatus

Abstract

The function of the cephalic lateral line in perceiving surface waves and its ecological significance was examined in the topminnow, Fundulus notatus (Rafinesque), a fish which frequents the surface waters. The sense organs are located in groups on the dorsal surface of the flatish head and are prominently visible on the skin. The individual organs of each group form a specific angle when related to the fish's midline. These organs perceive the force of slight surface waves and the perceptional field is omnidirectional. A great number of enucleated fish respond spontaneously, but when trained they orient toward the source of the disturbance on the surface up to a distance of 15 cm. The fact that the radiating wave is curved enables fish to locate the origin accurately. Fundulus notatus does not distinguish between two waves of equal strength striking simultaneously; it does so, however, if a time or intensity difference is present. A fish with sense organs removed from one side of the head deviates at a constant angle from the wave source. The perceptional field of individual organs or canals circumscribes a line drawn through the longitudinal axis of the organ or canal. A wave, therefore, traveling parallel to the longitudinal axis of the oval sense organ and hence the cupula, stimulates to the greatest extent whereas a wave perpendicular to it does not. The individual organs possess a directional property and, therefore, their arrangement on the head is functionally meaningful. The lateral line supplements the vision of the fish in finding its prey at the water surface.