Meeting Abstract
Suction feeding in cypriniform fishes may not fit other hydrodynamic models and the hyoid region likely plays a crucial role in generating intraoral subambient pressure to generate flow and pull food into the mouth. In unrelated acanthomorph fishes the hypaxial muscles were shown to generate power behind suction feeding and because those forces are transmitted through the hyoid, it has become of more interest. In cypriniforms the hyoid region may be of more functional relevance because some species are lacking the characteristic head lift movement in suction-feeding acanthomorphs. The hyoid apparatus includes multiple bones, joints, and linkages composed of diverse connective tissues that likely play differing functional roles. To characterize the composition of the tissues within the hyoid region in cypriniforms we examined three species: goldfish, Carassius auratus, zebrafish, Danio rerio, and blacknose dace, Rhinichthys atratulus. Based on histological stains of the hyoid apparatus we found varying types of cartilage-like connective tissues in functionally relevant structures. For instance, the ceratohyal of all species contained a medio-laterally oriented region of densely packed cells that stained consistently high for mucopolysaccharides, but this cartilage-like element did not fill the entire bone. The medial edges of the hypohyals are covered in a tissue that is distinct from the sternohyoideous tendon in between. This articular tissue is also comprised of densely packed cells with less extracellular matrix and lower affinity for the mucopolysaccharide stain. Throughout the entire hyoid region in all species, the hyoid elements were composites, staining for a range of mineralized and cartilage-like materials. These findings are important because they can inform our understanding how cypriniforms suction feed.
