MECHANICAL PROPERTIES AND LOCOMOTOR FUNCTIONS OF EEL SKIN

Abstract

1. The skin of the American eel Anguilla rostrata is composed largely of a crossed-helical array of fibers, believed to be collagen, that are oriented at an angle of 45° with the long axis of the fish. Uniaxial and biaxial tension testing of eel skin was used to assess the role of the collagen fibers in the locomotor functions of the skin.2. The elastic modulus of skin stressed in the circumferential direction of the fish is 14.6 MN/m2 while that of skin stressed in the longitudinal direction is 3.5 MN/m2, thus eel skin is an order of magnitude stiffer in the circumferential than in the longitudinal direction. The skin is stiffest in the direction of the fibers, having an elastic modulus of 0.16 GN/m2 in this direction. Within the range of in vivo extensions the behavior of skin stressed in the longitudinal direction is similar to that of a model consisting of continuous crossed-fibers, while that of skin stressed in the circumferential direction is not.3. The mechanical behavior of the skin indicates that the skin may act as an external tendon, transmitting forces arising in the axial musculature down the length of the fish to the tail.4. The collagen fibers within the skin may play an important role in torsion resistance when the eel executes its peculiar "corkscrew" motion.