Meeting Abstract
The elongate fish body form and anguilliform swimming mode evolved many times across taxa, suggesting a benefit from combining the two. In addition to the well studied 2D bending wave, some elongate fish twist about the long axis, producing a 3D wave of motion. Despite similar body plans and 2D swimming mode, the 3D wave varies across species. Some characteristics of vertebral anatomy may dictate parameters of the 3D wave. We compared vertebral structure to swimming behavior in eight elongate fish species. Using CT scans, we measured parameters including centra angle and diameter along the body. We found that centra angle is deep anteriorly (70-85 deg) and shallow posteriorly (50-65 deg) for all species. Centra diameter is large at the head (0.009-0.013 BL) and small at the tail (0.005-0.007) for most species. We then used 3D printed parts (vertebrae) and cast polymer (intervertebral joint) to construct physical models based on these measurements. Models were bent and twisted on a material testing system to determine effect of morphology on stiffness of the joints. Centra diameter is the best predictor of stiffness with larger diameters requiring less force to deform. We compared these data to mechanical tests done on fish and found that morphology may play a role in the mechanics of some species but not others. For example, the Penpoint Gunnel has a relatively constant centra diameter (0.0085 BL) from head to tail, and torsional stiffness is also constant (0.0005 Nm/rad). In contrast, the Black Prickleback has one of the largest decreasing gradients in centra diameter (0.012 – 0.008 BL) down the body, yet torsional stiffness still remains relatively constant (0.0005 Nm/rad). There is no clear trend between vertebral morphology and 3D kinematics, which may suggest an alternative mechanism for 3D control.
