Morphological Structures Correspond to the Location of Vertebral Bending During Suction Feeding in Fishes

Abstract

During suction feeding, many fishes use their epaxial muscles to generate a substantial amount of power to produce cranial elevation. When the muscles contract they reduce the angle between the head and body, causing the axial skeleton to bend dorsoventrally. Without axial bending, cranial elevation would be limited and feeding performance would decrease. The goal of this study is to locate where the vertebral column bends during suction feeding and relate this to the axial morphology of different species. We collected and analyzed live feeding data from three species (largemouth bass, pacific staghorn sculpin, and striped surfperch) using 3D animation techniques. CT scans were also analyzed with a focus on the shapes and spacing of the vertebrae, neural spines, and pterygiophores. Each of the three species had unique axial skeletons comprising differently shaped and spaced vertebrae, neural spines, and pterygiophores. We hypothesized that the axis of rotation for each species is located in the anterior-most region of the vertebral column, specifically between the vertebrae with the greatest space between the neural spines and pterygiophores. Our data show that the axis of rotation is consistent for largemouth bass (joints 3 and 4) and striped surfperch (joints 2 and 3), although both species bent at different intervertebral joints. These axes of rotation for both largemouth bass and striped surfperch correspond to the organization of the neural spines and pterygiophores. The staghorn sculpin presented an interesting case where all of its axes of rotation (joints 3, 4, 5, and 6) were not associated with any unique structures. However, cranial elevation increased at the more posterior joints. Given the great deal of interspecific variation of the axial skeleton, it is important to investigate the role of these different morphologies in suction feeding.