Puncture resistance of the scaled skin from striped bass: collective mechanisms and inspiration for new flexible armor designs.

The structure and mechanics of fish scales display unusual and attractive features which could inspire new protective materials and systems. This natural material is therefore attracting attention over the past few years, and recent work demonstrated the remarkable performance of individual fish scales. A puncture event as would occur from a predator's attack however involves more than one scale, and in this article we therefore investigate collective mechanisms occurring within the scaled skin of a fish in the event of a predator's attack. We first demonstrate that in striped bass (Morone saxatilis), the scales increase by four to five times the force required to puncture the skin. We show that individual scales from striped bass provide a remarkable barrier against sharp puncture, regardless of the stiffness of the substrate. The scalation pattern in striped bass is such that three scales overlap at any point on the surface of the fish, which we show effectively multiplies the puncture force by three. We determined that the friction between scales is negligible and therefore it does not contribute to increasing puncture force. Likewise, we found that the local arrangement of the scales had little effect on the puncture performance. Interestingly, because the scales are several orders of magnitude stiffer than the substrate, indenting a few isolated scales results in "sinking" of the scales into the substrate. The high local deflections and strain within the soft tissue may then result in blunt injury before the sharp indenter penetrates the scales. Stereo-imaging and image correlation performed around a puncture site in fish reveal that the surrounding scales collectively contribute to redistributing the puncture force over large volume, limiting local deflections and strains in the soft tissues. The structure and mechanisms of natural fish scales therefore offer an effective protection against several types of threat, and may inspire novel versatile protective systems with attractive flexural properties.

Effects of barotrauma and mitigation methods on released Australian bass Macquaria novemaculeata.

The effects of barotrauma on the short-term mortality and physical condition of Australian bass Macquaria novemaculeata were investigated after being: (1) conventionally angled and released during two tournaments in deep impoundments and (2) released untreated or subjected to venting or recompression during a manipulative experiment. All fish were released into two 20 m deep bathy-cages and monitored for 3 days. Of 238 M. novemaculeata angled during the tournaments, 43 (18·1%) had clinical signs of barotrauma or were vented and five of these later died (11·6% mortality). Catch histories varied significantly between both barotrauma and non-barotrauma fish and tournaments, but only hook ingestion significantly influenced mortality (P < 0·05). During the manipulative experiment, venting significantly influenced mortality (13·3%) compared to no treatment or recompression (no deaths). Magnetic resonance images and dissections of barotrauma fish indicated large variation among clinical signs. On the basis of these results, wherever possible M. novemaculeata suffering barotrauma should be immediately released with no treatment. Fish that are unable to resubmerge should be recompressed, while those held in live wells and released in shallow water should be vented.