Sharks have a reputation for being intimidating predators with rough, sandpapery skin. But are they slimy too? Let’s take a closer look at shark skin and anatomy to unravel fact from fiction.
If you’re short on time, here’s a quick answer: Sharks are not slimy. Their skin is made up of tiny teeth-like structures called dermal denticles that give them a smooth, sandpapery texture.
Shark Skin Anatomy: Scales and Dermal Denticles
Dermal Denticles Create Texture and Reduce Drag
Shark skin is composed of tiny tooth-like structures called dermal denticles. These denticles overlap like shingles on a roof to create the rough, sandpapery texture sharks are known for. But they serve an important hydrodynamic purpose as well.
The denticles are shaped like small diamond-shaped scales with ridges running down their length. This ridge shape helps reduce drag and turbulence, allowing sharks to swim faster and more efficiently through the water.
Researchers have found that the denticle structure can reduce surface drag by up to 9%. Engineers have even attempted to mimic shark denticles when designing aircraft, boats, and swimsuits to try to replicate this drag-reducing effect.
So while shark skin feels rough if you run your hand along it, the intricate arrangement of denticles actually helps sharks slice smoothly through the water.
Sharks Lack the Mucus Layer That Makes Some Fish Slimy
Many fish produce a thick, slippery mucus layer on their skin for protection and lubrication. This mucus is primarily composed of glycoproteins called mucins secreted by specialized goblet cells in the skin.
The abundance of mucus is why some fish, like hagfish, feel very slick and slimy to the touch.
Sharks, however, do not produce much mucus. They have goblet cells scattered throughout their skin that secrete small amounts of mucus. But nothing like the copious gelatinous layer that other fish have.
The limited mucus on shark skin mainly serves to protect against infection rather than improve hydrodynamics. So despite their fearsome, prehistoric appearance, sharks themselves are not slimy or slick-feeling like some other fish.
The lack of mucus production may correlate with sharks’ more rugged dermal denticles. Sharks rely on these tooth-like scales rather than mucus to reduce drag when swimming. And the exposed denticle ridges likely make mucus less effective compared to smooth fish skin.
So nature optimized sharks for rough, hydrodynamic skin rather than slime.
Shark Skin By Species: Smooth, Rough, and Prickly
Smooth Dogfish and Spiny Dogfish Sharks
The skin of smooth dogfish sharks feels smooth and velvety to the touch, hence their name. Their skin is composed of tiny teeth-like structures called denticles that point towards the tail, decreasing drag as the shark swims.
Research shows the denticles on smooth dogfish skin can reduce surface friction by up to 9% (source).
Spiny dogfish sharks get their name from the sharp, needle-like denticles covering their skin that can be painful to touch. The spines make them difficult for predators to swallow. Their skin is also smooth in the forward direction to allow fast, agile movement and hunting.
Bull Sharks and Their Tough Hide
Bull sharks live up to their name – they have extremely tough skin, more like armor than typical shark skin. Their hide is covered in hard, bony plates made of the same dentin material as shark teeth. These act as an outer skeleton, protecting vital organs from attack while also reducing drag (source).
Tests show adult bull shark skin to be thicker and more puncture resistant than many other shark species. Young bull sharks have less calcified skin until reaching maturity. The rough texture of mature bull sharks may play a role in mating rituals.
Prickly Bramble and Sixgill Sharks
The prickly hide of bramble sharks is entirely covered in sharp denticles, giving an abrasive texture. Their skin denticles are elongated with multiple points rather than smooth scales. The many spikes make bramble sharks troublesome for predators to bite and swallow.
Meanwhile, the broad sixgill shark has skin covered in diamond-shaped denticles, largest on the upper body. They are smooth if brushed from head to tail but rough and scratchy brushed tail to head. The specialized denticles allow low drag at high speeds with armor-like protection.
Benefits of Non-Slimy Shark Skin
Streamlined for Speed and Efficiency
Shark skin is covered in tiny, tooth-like scales called dermal denticles that create a smooth, hydrodynamic surface. This streamlined structure allows sharks to swim very efficiently and reach incredible speeds.
The scales overlap like shingles on a roof and point towards the tail, reducing drag as the shark moves forward. Some sharks can reach speeds over 60 mph thanks to their unique skin!
Research has shown that dermal denticles can reduce surface drag by up to 9%. This is a major advantage for predators like sharks who need to swim fast to catch prey. The denticles enhance water flow by channeling it to specific areas of the skin.
This streamlining helps sharks conserve energy as they cruise the oceans searching for their next meal.
Resists Parasites and Bacterial Infections
In addition to speed, the ultrasmooth texture and microscopic shape of dermal denticles limit foul organisms from gaining a foothold on shark skin. Parasites have difficulty latching onto and penetrating their tough external surface.
This helps sharks stay cleaner and healthier in the bacteria-filled ocean environment.
The grooved structure also discourages the growth of algae and other marine organisms by disrupting the contacted surface area. Less contact means it’s harder for plants and animals to anchor themselves.
This gives sharks a smooth, hydrodynamic advantage and prevents excessive drag which could slow them down.
Researchers found that the skin’s surface chemistry further prevents microbe transmission. Dermal denticles contain antibacterial properties that naturally inhibit bacterial growth. This bioactive surface helps ward off infection and disease without the need for immune response.
Inspires Innovative Technologies
Engineers and designers are looking to shark skin for bioinspiration. The dermal denticle structure has been mimicked to create swimsuits, boat hull coatings, and even bacteria-resistant surfaces. These shark skin-inspired technologies aim to synthesize the morphological advantages in man-made materials and devices.
For example, Speedo’s sharkskin-inspired LZR Racer swimsuit helped athletes break many swimming world records after its release in 2008. The ultra-thin, water-repellent fabric mimics shark skin by reducing form drag across the body surface.
This improves efficiency in the water by optimizing swimmer hydrodynamics.
Some antibacterial products contain shark skin-inspired texture coatings. The microscopic pattern limits bacterial contact and adhesion to the solid surface underneath. Sharklet Technologies uses this shark skin effect to create algae and bacteria resistant coatings for medical devices.
Marine architects look to the silent, streamlined shark for ideas on designing boat hulls that move smoothly through water. Riblets or microridges modeled after dermal denticles can be applied to ships to channel liquid flow and dampen turbulence across hull surfaces.
When Are Sharks Slimy?
Inside the Egg Case as Embryos
Shark pups are enveloped in a slimy coating called a mucous membrane when they are still developing inside their egg cases. This mucus layer protects the fragile embryos from abrasions and acts as an antibacterial barrier against infections.
The mucus contains special antibacterial proteins that prevent microbial growth, keeping the pups safe from harm as they grow. New research published in the Journal of Experimental Biology in 2022 analyzed the components of shark egg case mucus and confirmed its protective properties.
While enclosed in the egg case, shark embryos are extremely vulnerable. The mucus membrane shields their delicate skin and allows them to develop undisturbed. It also enables gas exchange through the porous egg case so the embryos can breathe.
Studies have found the mucus contains antiviral and antifungal agents as well. Without this nutritious, slippery coating, mortality rates of shark pups would be much higher.
The mucus is secreted by the embryo’s specialized epidermal gland cells and continues to be produced until the pup hatches. The slime keeps the pup hydrated and provides a medium for compounds that nourish the growing embryo.
So during their gestation period inside the egg case, shark pups are indeed slimy for very good reason!
Right After Birth as Newborn Pups
Most species of shark give birth to live young rather than laying eggs. The pups emerge enveloped in a thick mucus coating that helps ease their passage through the mother’s birth canal. This slippery mucus functions as a lubricant to reduce abrasion and facilitates the pup’s exit from the mother’s body.
In addition to aiding the birthing process, the mucus contains antibacterial, antiviral and antifungal properties to protect newborn sharks from pathogens. The coating may also help minimize the risk of microbial infection from the mother’s bodily fluids.
Without this protective slime barrier, mortality rates of newborn sharks would likely increase.
The mucus is produced by specialized epidermal gland cells and continues to cover the pup’s body for the first few hours until it wears off. So immediately after birth, shark pups have an external mucus layer that makes them appear quite slimy.
But this slippery coating soon dissipates as the pup starts actively swimming and foraging. Within the first day of life, newborn sharks lose their mucus membrane and no longer seem so slippery and slimy.
Conclusion
So in summary, sharks are not slimy to the touch under normal conditions thanks to the tiny placoid scales covering their skin. The tooth-like dermal denticles give skin a smooth, sandpapery texture instead.
Sharks only feel truly slimy as developing embryos inside egg cases and as newborn pups right after birth before their protective denticles fully form.
Understanding the unique properties of shark skin gives us a glimpse into sharks’ evolutionary adaptations for speed, efficiency, and protection from bacteria and parasites. Their non-slimy hide has even inspired real-world technological innovations over the years.
So next time you touch a shark, expect sandpaper, not slime!
