Abstract

ABSTRACTThe caudal fins of adult zebrafish are supported by multiple bony rays that are laterally interconnected by soft interray tissue. Little is known about the fin's mechanical properties that influence bending in response to hydrodynamic forces during swimming. Here, we developed an experimental setup to measure the elastic properties of caudal fins in vivo by applying micro-Newton forces to obtain bending stiffness and a tensional modulus. We detected overall bending moments of 1.5×10−9–4×10−9 N m2 along the proximal–distal axis of the appendage showing a non-monotonous pattern that was not due to the geometry of the fin itself. Surgical disruption of the interray tissues along the proximal–distal axis revealed no significant changes to the overall bending stiffness, which we confirmed by determining a tensional modulus of the interray tissue. Thus, the biophysical values suggest that the flexibility of the fin during its hydrodynamic performance predominantly relies on the mechanical properties of the rays.

Highlights

  • Here, we have described an apparatus to measure the bending stiffness of fins of live zebrafish at the level of 10−9 N m2, as well as a method to determine the tensional elasticity of the soft interray tissue to the level of kPa

  • Previous measurements of bending stiffness of larger fish have reached a sensitivity of 10−6 N m2 (Flammang et al, 2013), which in that case was sufficient because of the larger dimensions of the fins and rays of bluegill sunfish

  • Given the diameter of bluegill rays of 1–2 mm compared with 0.1– 0.2 mm for zebrafish, one would expect zebrafish rays to be more than four orders of magnitude more flexible than those of bluegill sunfish

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Summary

Introduction

Motion and the corresponding propulsive forces of flapping fins interacting with water flows have been a long-standing interest in biomechanics research (Iosilevskii, 2016; Borazjani et al, 2013; Witt et al, 2015; Esposito et al, 2012; Novarti et al, 2017; Dabiri et al, 2014; Nguyen et al, 2017; Fang-Bao et al, 2014; Noca et al, 1997; Verma et al, 2017). The shape, position and flexibility of fins display a high variability among fish taxa that accounts for a broad diversity of the locomotor functions. The main material of the fin consists of an array of similar bony elements (lepidotrichia) interconnected by soft tissue. Knowledge of the mechanical features of the functional tissue is necessary to understand how a deforming fin interacts with the surrounding fluid to generate swimming forces.

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