Dermal Denticles of Three Slowly Swimming Shark Species: Microscopy and Flow Visualization

Abstract

Shark skin has for many years inspired engineers to produce biomimetic structures reducing surface drag or acting as an anti-fouling layer. Both effects are presumed to be consequences of the structure of shark skin that is composed of arrays of so-called dermal denticles. However, the understanding of the full functional role of the dermal denticles is still a topic of research. We report optical microscopy and scanning electron microscopy of dermal denticles from three slowly swimming shark species for which the functional role of the dermal denticles is suggested as one of defense (possibly understood as anti-fouling) and/or abrasion strength. The three species are Greenland shark (Somnosius microcephalus), small-spotted catshark (Scyliorhinus canicula) and spiny dogfish (Squalus acanthias). Samples were taken at over 30 different positions on the bodies of the sharks. In addition, we demonstrate that the flow pattern near natural shark skin can be measured by micro-PIV (particle image velocimetry). The microfluidic experiments are complemented by numerical flow simulations. Both visualize unsteady flow, small eddies, and recirculation bubbles behind the natural dermal denticles.

Hydrodynamic efficiency in sharks: the combined role of riblets and denticles

“…Considerable variety in denticle shape can be observed (e.g. Figure 1), not only between different species, but also depending on the location on the body (Reif, 1985;Díez, Soto, and Blanco, 2015;Feld et al, 2019). The typical structure of a dermal denticle is detailed in Figure 2, although this can vary significantly between species (See e.g.…”

A bio-inspired approach for boosting innovation in the separation technology sector

“…The denticles are aligned along the body axis and have a diamond-like shape. They are generally formed by V-shaped riblets with variable length (around 130-700 μm), width (70-460 μm), height (25-500 μm) and spacing (100-300 μm) depending on the species of shark and the location on its body (42,63,64). The riblets work by impeding the cross-stream translation of streamwise vortices in the viscous sublayer.…”

Living naked: first case of lack of skin‐related structures in an elasmobranch, the blackmouth catshark (Galeus melastomus)

“…The tooth‐like dermal denticles represent the most external and characteristic skin structures. Because of their shape and composition, they provide a mechanical barrier, protecting the organism from environment, predators and ectoparasites, and also reducing potential mechanical abrasions (Feld et al ., 2019; Meyer & Seegers, 2012). It has been proved that they facilitate locomotion by reducing the friction with water and by altering the hydrodynamic flow on the body surface (Oeffner & Lauder, 2012).…”