P3.177 Friday, Jan. 6 Mechanical properties of the skin of the Pacific hagfish, Epatretus stoutii DEMAS, A/D*; CLARK, A/J; College of Charleston; College of Charleston firstname.lastname@example.org
Hagfishes possess minimal tendinous connections between the skin and axial muscles that power locomotion, which gives their skin a loose-fitting appearance. This contrasts the tighter-fitting skin in lampreys, cartilaginous fishes, and bony fishes, which are due to numerous muscle-skin connections. Axial bending during swimming produces tensile stresses that must be accommodated by the skin, therefore we hypothesized that the loose-fitting skin of hagfish is less resistant to tensile stress in comparison to other fish species. We performed quasi-static uniaxial tensile tests to failure on various skin samples from five individual Pacific hagfish to determine skin strength (peak stress) and stiffness (resistance to deformation). Skin samples were obtained from dorsal and ventral surfaces of the body and tensile loads were applied in longitudinal and orthogonal directions. On the dorsal surface, the skin of the Pacific hagfish is anisotropic, being significantly stiffer in the longitudinal direction (47.1 MPa) than in the orthogonal direction (28.0 MPa). This pattern contrasts the anisotropy observed in other fishes, which possess skin that is stiffer orthogonally than longitudinally. Decreased resistance to deformation of hagfish skin in the orthogonal direction probably facilitates torsional movements characteristic to knotting. Furthermore, the tensile strength and stiffness of Pacific hagfish skin is comparable to that in terrestrial vertebrates and other fishes, including elongate species like the American eel, and fast-swimming species like skipjack tuna.