Meeting Abstract
Fish skin is a complex biomaterial containing collagen fibers that wrap around the body in half a helix pattern on each side. Various researchers have hypothesized functions for the fibers, but we have relatively little data on their functional role during swimming or their distribution across species. Past studies showed that fiber angle and the material properties of the skin vary along the length of the fish. However, they have not examined the correlation between the angle of the collagen fibers and the material properties of the fish skin. Engineering and model studies suggest that there are two critical angles in fiber wound tubes. Fibers at 45 degrees maximize torsional stiffness, while fibers at 55 degrees resist buckling and prevent changes in length due to internal pressure. In this study, we quantified collagen fiber angle in eight species of fishes with known swimming kinematics and created physical models to determine the passive effects of skin fiber on the mechanics of the body. We found that collagen fiber angles in these fishes generally fall between 45 and 55 degrees. Change in angle along the length of the body is correlated with species and habitat. Body twisting during swimming and torsional stiffness also correlate with fiber angle, though the sign of that correlation differs between groups from different habitats. We also found that there is a nonlinear relationship between fiber angle and bending stiffness in our physical models. These results show that skin fiber angles may have a complex but important role in the passive mechanical properties of fish bodies, and may ultimately affect swimming performance.
