Meeting Abstract
The convergent architecture of the skin of aquatic vertebrates, with its multi-layer, cross-helically arranged collagen fibers, has led biomechanist to infer that the dermis plays an important functional role in undulatory swimming. To date, two functions have been proposed for the skin of ray-finned fishes: (1) an exotendon in which the cross-helical fibers resist deformation and transmit force down the exterior of the body and (2) a direct-force transmission device in which the contractile tension developed in anterior muscle segments is propagated to the peduncle and caudal fin. In addition, skin stiffness may be related to ecological and morphological parameters that demand different optima concerning body thrust production (including swimming mode, body shape, and feeding). In this study we set out to determine the skin stiffness of fishes demonstrating a variety of swimming modes and feeding strategies, from burst swimming ambushers to steady swimming foragers. We laser cut prepared skin samples and tested each in a custom, Ardiuno-based biaxial testing rig that imposed positive strain along the longitudinal axis of the sample while hoop stress was kept constant. Across all species at 10% longitudinal strain and a constant hoop stress of 0.1 MPa, longitudinal stiffness ranged from 23 and 52 kPa and from 46 and 270 kPa at 30%. From these data, we found a positive relationship between skin stiffness and species demonstrating high-acceleration swimming performance. We also found that for two out of out four flatfishes, skin stiffness showed eyed versus blind side asymmetry. Together, our results suggest that the skin and its material properties contribute directly to swimming performance capabilities and a number of ecological demands.
