Have you ever wondered if fish have eyelids? do they need them? Do they blink? What do they use them for?
I have been asked this question a lot recently so I thought I would write this article to answer the question.
Do Fish Have Eyelids?
Fish do not have eyelids, the reason is because the cornea is not exposed to air, when exposed to air it can dry out the eye and also get dust in it.
Fish stay underwater, so they have little or no risk of exposing their cornea to air. The eyelids’ function is to protect the eyes, but this protective measure is not very useful to fish. Fish do not have eyelids to protect their eyes, but they make use of other mechanisms.
One of the ways fish protects their eyes is the use of a thick protective layer. This protective mechanism is common in most fish. It protects the eyes by providing a transparent or translucent film over the eyes while maintaining perfect vision.
Fish also have various means of protecting their eyes from attack. Some fish have a sharp reflex that makes them dodge eye-crushing attacks, and some have eye-like structures or spots at their rear, giving predators fake information about their eyesight.
Fish will do well without eyelids as they will always find a way to protect their eyes and cornea.
Why Do Fish Do Not Have Eyelids?
Fish do not have eyelids because they do not require most of its functions. The function of the eyelid it to moisten the eyes which is not required for fish.
Fish have other means to provide the functions of the eyelids.
Eyelids make sure the eyes do not dry up, continually maintaining moisture by distributing tears. Fish stay in the water and have enough resources to keep their eyes moist. So, the eyelid is quite useless to the fish as it can keep its eyes moist, even after death.
Another function of the eyelid is to protect the eyes from particles in the air, like dust and dirt. Fish have but few reasons to come out of the water, not to talk of exposing their eyes in the air long enough to attract dirt. Since they stay underwater and have little reasons to come out of the water, they do not need eyelids.
Since fish also have structures that will provide the eyelids’ protection, they will not need it. We can’t say if they would evolve into having eyelids, but they have no reason to worry about it as it stands.
What Kind of Fish Have Eyelids?
Most fish do not have eyelids, with the shark as the only exception. Sharks have eyelids that protect their eyes. The eyes of a shark are very similar in structure to humans; they have a retina, iris, lens, cornea, pupils, etc., like humans. The difference between the shark and human eyes is the presence of a structure called tapetum lucidum.
This structure gives the shark a powerful vision, which is ten times greater than that of humans. The eyelid in a shark is the third eyelid, called the nictitating membrane. This membrane is a transparent or translucent eyelid that protects the eyes of the shark.
Although sharks have these eyelids, they do not blink their eyes because the water helps them wash their eyes. They only make use of this structure to protect their eyes, especially when feeding on prey. The eyelid comes from the medial canthus and covers the eye providing the needed protection.
Do Fish Blink?
Blinking is an everyday survival or protective mechanism that humans and other animals exhibit. Blinking is a natural reflex action, but it does not occur in fish. There are several reasons why fish do not blink their eyes; here are some
- Absence Of Eye Lids
- Water Dwelling
- Protective layer
Absence Of Eyelids
The organ that aids blinking in animals is the eyelids, which is absent in fish. The upper and lower eyelids perform the blinking; the upper and lower lids move towards each other disrupting vision in split seconds. If there is no eyelid to move up and down or sideways, then there is no blinking.
Fish do not have eyelids that can close, causing them to blink. Even sharks with a third eyelid do not blink; they only cover their eyes to protect them.
One of the reasons humans and other animals blink is to protect the eyes from dust and dirt in the air. There are lots of particles and dirt in the air that can get into the eyes and cause problems. The eyes blink when these particles come close, shutting them to prevent them from entering.
Fish dwell in water and have little or no reason to come out of it, so they do not need an eyelid to save them from dirt in the air. Even the ones that come out of water do not stay out long, making the chance of dirt entering the eyes slim.
Another vital purpose of the eyelids is to maintain moisture in the eye by even distribution of fluid across the eyes when you blink. There are glands in the eyelids that produce enough moisture to keep the eyes wet and prevent them from drying. When the eyes dry up, the functionality of the eyes reduces.
Fish do not have this problem as they always have their eyes full of moisture. The water also helps them wash their eyes regularly, providing enough moisture to keep their eyes wet, better still, full of water.
Since the eyelid’s function is to provide the needed protection to the eyes; fish do not need their service as they possess a film or layer that runs across the eyes. The film protects the eyes and keeps them safe. Some people even have it that the layer acts like a glass allowing fish to focus on substance in the water.
Do Fish Close Their Eyes?
It is quite difficult, if not impossible, for fish to close their eyes without having eyelids. The eyelids come together, creating a layer of skin that covers the eyes and closes them. Fish do not have these eyelids, making it impossible for them to close their eyes.
Even while having a deep rest, fish have their eyes open, and their pupils can still monitor animals’ movement around them. When animals sleep, a part of the brain, the neocortex, shuts down, allowing them to sleep.
Fish do not have this part of the brain, so they do not sleep but only rest. They always have their eyes open day and night. What a creature!
Do Fishes Cry?
Unlike humans, fish don’t have a cerebral cortex, setting us apart from them. Fish can’t cry, although they can get depressed, hurt, etc. They also do not produce tears as they do not have tear glands; they have enough water resources to keep their eyes moist.
Fish do not have eyelids and do not have reasons to shut or close their eyes. The only fish with eyelids is the shark, and a third eyelid called the nictitating membrane. This membrane is not a true eyelid but performs an eyelid function except blinking, moisturizing, etc.