Do Fish Have Eyelids? The Surprising Reason Why They Don't Blink

Aashita Dhingra
Oct 25, 2023 By Aashita Dhingra
Originally Published on Nov 18, 2021
Fish eyelid facts and why they don't blink.

Fishes love swimming, whether it is a surface fish, deep water fish, or aquarium fish, all of them like swimming and continue to do so for most parts of the day.

They respond to threats by quickly moving away and evaluating the surface of the water around them. This helps them to know about predators in the water and see their movements.

Do fishes have eyelids? No, fishes do not have eyelids. Fishes notice the marine life around them and respond to movements accordingly.

They are not threatened by related species but are extremely cautious of sharks and other big fishes. Usually, small fishes stay in groups and are vigilant even when they sleep.

They can respond quickly to danger and see their surroundings. Do you still want to know that do fish even sleep or think about how they usually live in the water? Then read on to understand if fishes close their eyes when they are sleeping, afterward also check, do fish have blood and do fish have livers?

Do fish have eyelids?

Humans have eyelids to protect eyes from dust and ensure that eyes stay moist but fish eyelids will be of little use in this regard. Since no dust particles are flying around in the water and the water ensures that the eyes are not dry, fishes do not need eyelids. So, fishes do not have eyelids.

How do fish sleep when they do not close their eyes and do not have eyelids? They can sleep with their eyes open!

All they do while sleeping is remain motionless towards the bottom of the water or the surface and some may even tuck themselves in a secure secret hiding spot.

Fishes respond very slowly if they feel the slightest movement in the water while asleep. Some fishes sleep during the day and remain active in the morning, while others are like humans and sleep only during the night.

As per scientists, some fishes have a transparent eyelid that protects them against objects or particles present in the sea. These transparent eyelids allow the fish to view objects more clearly.

Certain other species of fish such as sharks have eyelids that help protect their eyes when they engage in fights to get their food or attack others in the water.

Whether it is goldfish, betta fish, clownfish, or any other aquarium fish, none of them have eyelids. They sleep when they find their surroundings to be darker than usual and swim to the bottom to remain motionless and rest.

They do not close their eyes while sleeping. They cannot shut their eyes mostly because there is no eyelid to help them do so.

Do fish blink?

Since most fishes do not have eyelids, they cannot blink. The fishes that do have them, tend not to blink as it helps them to stay vigilant and aware of their surroundings at all times. Moreover, fishes can sleep without closing their eyes.

Certain species of fish have transparent membranes functioning as protective eyelids to ensure that the fish can see irrespective of how deep the water is. Scientists claim that those species that have transparent eyelids are more proficient in seeing underwater objects and animals than the other fish species.

Fishes do not blink their eyes. Species like sharks have eyelids but they are only meant for protection from damage. They do not have any other function.

Unlike humans, the fish do not blink. Sharks do not need to blink as their eyes are kept moist by the water itself. The water around their body keeps their eyes clean and moist, therefore rendering the use of blinking.

Fish blink is a sight that is usually not seen. Without eyelids, a fish blink is not possible and moreover, there is no need for it. Though the sight of a fish might often raise such questions, the answer is very obvious. Irrespective of the time of the day, fish do not blink.

Only function of eyelids in fishes is to protect from damage.

How do fish sleep with their eyes open?

Most fishes that we encounter in the aquarium and the surface of water do not possess eyelids and therefore tend to sleep with their eyes open.  As most species of fish stay awake during the day, they swim towards the bottom of the water or dark caves when it is night. There they then remain and rest.

Their movement is slow and they do not notice their surroundings much during this period. Some of these marine animals stay close to the water surface while others go towards the bottom where light does not reach.

Even where there is a lack of light, fishes understand whether it is day or night. The lack of light does not prevent these animals from swimming around freely.

Some fishes like the dolphins sleep with one eye closed to ensure that they are aware of predators near them. They stay alert to respond to close threats. They sleep with one eye open to keep half of their brain awake and continue breathing.

Unlike humans, dolphins cannot breathe if they sleep with both eyes closed. Their breathing is conscious and therefore will take place only if their brain remains awake. If they shut their eyes, their breathing would stop.

How do fish dream with open eyes?

It is easier to notice the fish in the aquarium. If you look closely, you will notice that fishes like goldfish and other aquarium species tend to drift slowly towards the bottom of the tank when the lights are turned off or dim lights are switched on.

Fishes keep moving in the water even when they are asleep to allow their gills to constantly absorb oxygen for the body. The gills take in air from the water and regulate it to provide oxygen to the fish.

The underwater fish may search for their predators and search for their food when they wake up. They rest during the night away from the light. It is interesting how different animals have different sleep patterns and ways of sleeping.

Though there is still not much information on whether fishes dream or not, the researches conducted so far suggest that fishes do experience a dream-like state. They sometimes change their colors while sleeping to portray the same.

However, much more research is needed in this area before drawing conclusions and generalizing the dreaming concept in marine life. Scientists have been increasingly studying the work of eyelids, the sleeping patterns of various species of fish, and their ways to respond to predators to understand this further.

Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for do fish have eyelids then why not take a look at do fish have tongues or do fish need oxygen?

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Written by Aashita Dhingra

Bachelors in Business Administration

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Aashita DhingraBachelors in Business Administration

Based in Lucknow, India, Aashita is a skilled content creator with experience crafting study guides for high school-aged kids. Her education includes a degree in Business Administration from St. Mary's Convent Inter College, which she leverages to bring a unique perspective to her work. Aashita's passion for writing and education is evident in her ability to craft engaging content.

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