Sensory innervation and proprioception of fish fins
While the role of pectoral fins in fish swimming has been studied in depth, little is known of how these fins receive proprioceptive feedback (sensory feedback corresponding to body position and movement). We selected the bluegill (Lepomis macrochirus), a species that uses its pectoral fins extensively during swimming, as a model organism for exploring fin proprioception. In this study we examine the responses of these nerves to sinusoidal and step-and-hold bending of the fin rays. We demonstrate that the sensory nerves innervating the pectoral fins of bluegills are capable of conveying proprioceptive feedback in response to fin bending, using extracellular physiological recordings in a fictive fin preparation. Activity recorded in response to these stimuli show that sensory nerve fibers respond to the magnitude and the velocity of the bending movement in biologically relevant ranges of actuation. Additionally, we used spike-sorting analyses to examine the responses of individual afferents to aspects of fin ray bending. These computational approaches suggest that there are multiple types of mechanosensory neurons responsive to fin ray bending and that these populations of neurons may communicate different properties of the bending stimulus. The feedback provided by these neurons may allow the pectoral fins to act as mechanical sensors as well as propulsors indicating more diverse roles for the fins than previously recognized.