Journal
JOURNAL OF EXPERIMENTAL BIOLOGY
Volume 216, Issue 22, Pages 4256-4263Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jeb.085753
Keywords
elasmobranch; spinal deformity; vertebrae; skeletal biomechanics; material properties
Categories
Funding
- Association of Zoos and Aquariums Conservation Endowment Fund
- Disney Worldwide Conservation Fund [08-856]
- Jacarlene Foundation
- The Bernice Barbour Foundation
- The University of Tampa College of Natural and Health Sciences
- The Spurlino Foundation
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Approximately 35% of sand tiger sharks (Carcharias taurus) in public aquaria exhibit spinal deformities ranging from compressed vertebrae and loss of intervertebral space to dislocated spines with vertebral degeneration and massive spondylosis caused by excessive mineralization both within vertebrae and outside the notochordal sheath. To identify the mechanical basis of these deformities, vertebral centra from affected (N=12) and non-affected (N=9) C. taurus were subjected to axial compression tests on an MTS 858 Bionix material testing system, after which mineral content was determined. Vertebral centra from affected sharks had significantly lower mineral content and material behavior in nearly all variables characterizing elasticity, plasticity and failure. These mechanical deficiencies are correlated with size at capture, capture method, vitamin C and zinc deficiency, aquarium size and swimming behavior in public aquaria. Non-affected C. taurus had greater stiffness and toughness even though these properties are generally incompatible in mineralized structures, suggesting that the biphasic (mineralized, unmineralized phases) nature of chondrichthyan vertebrae yields material behavior not otherwise observed in vertebrate skeletons. However, vertebral centra from non-affected sharks had lower mineral content (33%), stiffness (167 MPa), yield strain (14%) and ultimate strength (16 MPa) than other species of sharks and bony vertebrates, indicating that biomechanical precautions must be taken in the husbandry of this species.
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