Exploring the Tactile and Gustatory Capacities of Fish Fins

Animals use appendage-based sensation to modulate behaviors ranging from locomotion and feeding to reproduction and object manipulation. Sensation is fundamental to many tetrapod limb functions, yet it has until recently remained largely uninvestigated in the paired fins of fishes, the limb homologues. Sensory feedback via fins can provide important information on the surrounding environment as well as on a fish's physical interactions within it. This thesis explores the capacity of fish fins to function as multimodal sensory devices in touch and taste. In chapter two, I investigate whether membranous fins may function as touch sensors. I show that fin ray afferents innervating the pectoral fin of the pictus catfish (Pimelodus pictus) are sensitive to pressure and light surface brushing, thus expanding the known known sensory repertoire of paired fins. In chapter three, I investigate touch and potential texture encoding mechanisms in the pectoral fins of the round goby (Neogobius melanostomus). I show that fish can sense coarse tactile features of their near range physical environment via fins with similar morphology and response properties to other vertebrates. In chapter four, I investigate the distribution of taste buds across the paired fins of several pomacentrids (damselfishes). While damselfish exhibit fewer taste buds than many other benthic species, I show taste buds are found at localized densities of up to 200/mm2 and exhibit variation in their distribution across species and fins that likely reflect differences in the functional demands for chemical sensation. In chapter five, I synthesize these results more broadly and identify future research directions that will further elucidate the morphology and structure-function relationships that underpin fins as multimodal sensors.