Most fish aren’t capable of blinking, but some sharks do. These creatures have a membrane around their eye called a nictitating membrane. This membrane protects the eye from irritants. This nictitating membrane is similar to the cilia found on our eyes. Sharks also have a nictitating membrane. As a result, they have the ability to control the amount of light that enters their eyes.
In fact, some sharks have eyelids, but the purpose is primarily protection. Some species have eyelids that close during feeding or when they fight. Others have a nictitating membrane that slides over their eyeball for protection. This membrane may also serve as a type of reading glass. Regardless of the reason, it’s interesting to think that sharks can blink their eyes! So, what makes them different from us?
Most fish can’t blink, but sharks don’t. This is because their eyelids don’t serve a purpose. They just close their eyes while sleeping, because their brain activity is so much higher when they’re sleeping. The brain activity during these hours is higher than when they’re awake. However, the Great White Shark never stops moving, as its movements help push oxygenated water over its gills.
While the majority of fish don’t blink, a few species of sharks have nictitating membranes. These membranes help keep the eye surface moist. Some species, including the plecostomus, also use their eyelids to blink. These species can blink their eyes, but not regularly. While this is a curious observation, sharks do not need to blink regularly. In fact, they can sleep up to three years without blinking.
The eyes of sharks are similar to those of other vertebrates. They have retinas, lenses, and corneas, and a tapetum lucidum tissue behind the eyelid that enhances their visibility in murky water. However, they do not blink because the water in their eyelids cleans them. They roll their eyes backwards when fighting and thus protect their eyesight. In addition to the nictitating membrane, sharks also have eyelids. The Great White shark does not blink, but instead rolls its eyes inwards.
It is not known if sharks blink their eyes, but sharks’ eyes are filled with a saline solution that is similar to blood plasma. The ocelli in sharks are particularly sensitive to light, which means that they can see rabbits 3.5 times farther than the human eye. If they do not see light, they can’t discriminate between colors, so they cover their eyes with their membranes when they hunt.
While most species of sharks have nictitating membranes, 15 have no such membranes. This doesn’t mean that they don’t protect their eyes; many species don’t need them to survive. The great white shark rolls its eyes backward when it attacks its prey, mating, and bumping into objects. In this manner, the great white shark appears to be ghostly when it attacks its prey.
While many fish have transparent eyelids to protect their eyes and see their surroundings more clearly, sharks don’t. Their eyelids are made to protect their eyes from debris and protect their eye tissues. This allows them to see in low-light conditions, making it possible to hunt at night. Unlike other animals, sharks do not blink when they sleep. In fact, they are very cautious and will rarely approach humans without protecting their eyes.
While the Great White shark isn’t known to blink its eyes, it does have a highly developed olfactory system. Some species can detect the presence of blood in seawater. Others have a strong olfactory sensitivity, making them attracted to sewage outfalls. Their eyelids have special sensory pores on their head. Some shark species also have external barbels on their skin. This enhances their ability to detect prey.