Abstract: The mechanical properties and structures of fish scales have generated considerable research interest, however, comparative studies for different fish scales from different water regions have not been reported. In this paper, the surface morphologies, hierarchical structures and mechanical properties of four kinds of fish scales collected from freshwater, shallow sea, and deep sea in New Zealand are investigated. The results indicate that the surface morphologies of those fish scales are similar at ventro-lateral, dorso-lateral and anterior locations, and the hierarchical structures of those fish scales all consist of two layers: a bone layer and a collagen layer composed of collagen fibrils. However, the spiral angles of the collagen lamellaes of different scales are different. The largest are Mugil cephalus scales, while the smallest are Cyprinus carpio scales. Comparing the mechanical behaviors of those fish scales, the tensile strength of Carassius auratus scales is the largest, but the ductility is the lowest. Pristipomoides sieboldii scales have the best ductility. Further, the relationship between hierarchical structures and mechanical properties of fish scales is discussed. It is found that the spiral angles of the collagen lamellaes and bond/collagen thickness ratio both have a great influence on the mechanical properties of fish scales. 

Key words: morphology, hierarchical structure, mechanical property, fish scale, water region