Thyroid Ablation Alters Passive Stiffness and Swimming Kinematics in Zebrafish

Locomotion behavior is ultimately determined by the integration between active and passive tissues of an organism, but little is known about how these properties develop or are maintained. In this study, we used zebrafish (Danio rerio) to address the effects of a developmental hormone on morphogenesis and mechanical integration during swimming. We analyzed common kinematic variables and estimated intervertebral joint (IVJ) stiffness of zebrafish reared under different thyroid hormone profiles (euthyroid and hypothyroid) swimming during two different forward speeds, 5 and 10 BL{middle dot}s-1. We found that zebrafish reared under hypothyroid conditions swam with higher trailing-edge amplitude, a larger amplitude envelope, longer propulsive wavelengths, and lower values of lateral strain in posterior regions at both speeds. IVJ second moment area about the bending axis was greater in the TH-, a result of a change in vertebral shape compared to wildtype fish. We conclude that thyroid hormone contributes to axial design during development and therefore has an important role in determining flexural stiffness and the swimming behaviors that are affected by this important property.