Meeting Abstract
Most fishes have taut skins, preloaded in tension, that can efficiently transmit muscular force during locomotion, store and return elastic energy, and control body shape deformations. Hagfish, however, have very loose skins that do not function this way during swimming. There are two hypotheses for the adaptive function of loose skin: it may be required to form and manipulate body knots; it may also protect the body core from predatory bites. Here, we evaluate hagfish skin looseness as a defense against biting attacks by performing ASTM F1306 puncture resistance tests that account for different degrees of skin looseness. We measured the force, probe displacement, and energy required to puncture samples of loose and preloaded hagfish skins, skins of other fish, and samples of various manmade films. These data were then correlated with morphological descriptions (skin thickness, fiber type and orientation) of skins using standard paraffin histology and light microscopy. Preliminary results show that similar amounts of work are needed to puncture hagfish skins and other fish skins. In contrast to other fish skins, puncturing hagfish skin necessitates less force but the slack fit imposes low to negative levels of preloading that result in significantly longer penetration distances. This longer travel by the probe, or tooth, before actual work is done to puncture the skin, may result in reduced damage during an assault. The benefit of loose skin to hagfish may be twofold: Puncturing loose skin requires more energy than taut skin of similar penetration force and biting baggy skin requires teeth to travel further in order to puncture. This extra distance and time may allow the loosely attached body core to slip out of harm’s way or even evade the attack altogether.
