Meeting Abstract
Mechanosensation is fundamental to many tetrapod limb functions yet remains largely uninvestigated in the paired fins of fishes, limb homologs. Despite the diversity of pectoral fin functions across taxa, research has focused on species whose fins experience significant deflections during locomotion or active foraging. Here we examine whether fins may function as passive sensory structures for touch sensation in the absence of extensive fin ray movement. To test this idea, we investigated the pectoral fins of the pictus catfish (Pimelodus pictus), a species that lives in close association with the benthic substrate. The fins have a robust leading edge spine and kinematic analysis showed that the spine and trailing fin rays are splayed at a consistent angle relative to the body axis during routine swimming and thus do not appear to be used to generate propulsive force. The fins are highly innervated with nerves running from the base of the fin to near the fin rays’ distal tips and antibody staining suggests the presence of mechanoreceptors at nerve fiber endings. To test for the ability to sense mechanical perturbations, fin ray nerve fiber activity was recorded in response to touch and bend stimulation. Afferent nerves from the pectoral fin responded to touch stimuli with little or no observable fin ray bending. Both pressure exerted perpendicular to the dorsal fin ray surface and brushing along the ray generated afferent nerve spiking. Fin ray nerves also responded to deflections of the rays. These data indicate that the pectoral fins of P. pictus can function as passive mechanosensory surfaces, providing feedback on benthic surface features and other aspects of the physical environment.
