If you are lucky enough to have touched a shark, you’ll notice that its skin has a very interesting texture. When stroked from head to tail, it generally feels smooth. But do it in the opposite direction, and you’ll find that it feels rough like sandpaper.
The reason lies in the tiny flat V-shaped scales that cover its skin. Called dermal denticles, these scales are surprisingly more like teeth than fish scales.
Like our teeth, dermal denticles have an inner core (made up of connective tissues, blood vessels, and nerves) covered by a layer of hard calcareous material called dentine. This is then covered with a hard enamel-like vitrodentine.
Made for speed and protection
One of the main functions of dermal denticles is to protect the shark from predators. At the same time, it has an equally important hydrodynamic function.
Dermal denticles have grooves running down their length in alignment with water flow. These grooves disrupt the formation of turbulent swirls of slower water, hence decreasing drag and turbulence, which allows the shark to swim faster and more stealthily.
Dermal denticles are so effective that swimsuit companies have designed racing suits that mimic the concept of dermal denticles. These specialty suits have helped Olympic swimmers achieve even faster times in the pool, but have since been banned at major competitions.
Here’s another interesting fact: for centuries, sushi chefs in Japan have been using graters lined with shark skin to grate wasabi root. The rough shark skin enables the wasabi to be grated to a much finer consistency so as to better bring out its flavour.