Mechanics of Pharyngeal Teeth of Black Carp (Mylopharyngodon piceus) Crushing Mollusk Shells

Authors

  • Chong He,

    1. Department of Mechanical Engineering, the Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, P. R. China
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  • Wu Zhou,

    1. Institute of Applied Mechanics, Zhejiang University, Hangzhou 310027, P. R. China
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  • Hongtao Wang,

    1. Department of Mechanical Engineering, the Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, P. R. China
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  • San-Qiang Shi,

    1. Department of Mechanical Engineering, the Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, P. R. China
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  • Haimin Yao

    Corresponding author
    1. Department of Mechanical Engineering, the Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, P. R. China
    2. The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, P. R. China
    • Department of Mechanical Engineering, the Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, P. R. China
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  • The authors thank Mr. JQ Yao for assistance in sample collecting. We also acknowledge Dr. Vengatesen Thiyagarajan's group at Hong Kong University for providing assistance in FESEM imaging. Supports for this work from the Early Career Scheme (ECS) of Hong Kong RGC (Grant No. 533312), the Departmental General Research Funds and Internal Competitive Research Grants (4-ZZA8, A-PM24, G-UA20) from the Hong Kong Polytechnic University and the Natural Science Foundation of China (Grant No. 11072273) are acknowledged.

Abstract

Mollusks such as snail and mussels adopt hard shells to protect their vulnerable bodies. Recent studies on biomaterials have revealed that these shells especially the nacre layers exhibit excellent mechanical properties, inspiring a number of biomimetic endeavors. Nevertheless, in nature, there is a species of fish called Mylopharyngodon piceus or black carp, whose main diet is exactly snails and mussels. Does such unique diet imply that the pharyngeal teeth of black carp, its major masticatory apparatus, are superior to the mollusk shells in mechanical properties? In this paper, structural and mechanical characterizations are conducted on the pharyngeal teeth of black carp, showing that enameloid, the outermost layer of black carp teeth, possesses similar elastic modulus and hardness in comparison to those of the pond snail shells. To shed light on the mechanics underlying the capability of pharyngeal teeth to crush mollusk shells, parametric studies on the geometry of the shells are conducted by means of finite element method. It is found that whether a mollusk shell is crushable or not, for given pharyngeal teeth, depends on the radius (R) and thickness (t) of the shell. A predation map for black carp teeth is constructed by delimiting the tR plane into three phasic regions corresponding to three possible consequences of the mechanical competition between pharyngeal teeth and shells. It is interesting to notice that all the freshwater shells chosen at random fall in the crushable regime while the seashells do not necessarily. This feature of black carp teeth can be speculated as a result of evolution in response to its freshwater diet.

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