Meeting Abstract
Bottom dwelling fishes interact with the substrate using their fins and have the ability to sense touch using mechanosensory afferents. Characterization of response properties as well as targeted immunostaining has revealed distinct populations of mechanoreceptors in the fin. Here we investigate 1) how the pectoral fins of the round goby (Neogobius melanostomus), a bottom dwelling species, are positioned and move during substrate associated behaviors, 2) whether fin functional regionalization relates to sensory morphology, and 3) how afferents encode relevant information about substrate contact. At rest as well as during movement, a degree of fin ray bending and lateral shear movement across contacted surfaces occurs. Substrate contact is primarily localized to the medial aspect of the ventral-most fin rays at their distal tips. Immunolabeling reveals regionalization of mechanoreceptors, as Merkel cell density decreases sharply in the distal tips. Using linear brush stimulations, we show afferents at the distal tips where substrate contact is highest exhibit small receptive fields (~2-4mm) and little variability in response onset to a repeated stimulus. As stimulus velocity increased, the mean firing rate associated with these afferents’ receptive field increased suggestive of a possible velocity encoding mechanism. In response to textured patterns of varying coarseness, a subset of the mechanoreceptor population spatially encode coarse surface features with high precision. The response of these afferents to a given texture is speed invariant and appear better suited to encoding coarser textures. The data suggest that much like the tetrapod somatosensory system, fins exhibit sensory and functional regionalization that facilitate the encoding of substrate features such as motion velocity and substrate roughness.
