Can fish see water? Can they see in the dark?

By Nadine Oraby | 2020 Update

In the depths of the vast blue ocean, where the sunlight doesn’t reach, do you ever wonder if the fish can see in the dark? More importantly, can it see in the water at all?

The answer isn’t so simple as a yes or no. There can’t be a definitive answer when there are so many fishes in the sea, literally. To give you an idea, scientists claim there are 3.5 trillion fishes in the world. This is 454 times more than the total number of humans on this planet. And guess what? Scientists think there are many more undiscovered fish breeds. For all we know, 3.5 trillion is just half of them, and I can’t honestly say that every single one of them can see water, or see in the dark.

However, this won’t stop me from finding a conclusive answer. Today, I plan to take you along a journey to learn all about it.

Can fish see water?

The short answer – nope. The long answer? You know how humans can’t see air, that is the same case with fish and water. Humans can’t see air like fish can’t see the water because their brains are trying to filter out unnecessary information like noise and smells. It saves brain power and uses it on other more important functions that can help us survive.

I bet the biggest question people have is; if humans can’t see air but see the water, can fish see the air? Unfortunately, no, a fish can’t see air. The fish’s vision depends on reflective light, and as air doesn’t have any reflective surface, fish don’t see air.

If it helps, a fish can see above water. I’m only speaking for the fish that live in the daylight zone. These little guys have 4 eyes, yes, four. Now, when I say 4, don’t expect to see a fish with 4 eyes staring at you. They still have 2 eyes, within which you will find 4 corneas – two of them are to help see underwater, and the other two are to help them see above the surface.

Can fish see water? (Video)

Can a fish see in the dark?

Yes! In the dark depths of the oceans, the sensory system called lateral line gives fish sight. What is lateral line? It is an organ that detects movement, pressure, and vibration within the water. It helps a fish become aware of their space, and as a result, allow them to become a better navigator.

Fun fact: There are some fish who have large eyes to detect the light illuminating from the starry night sky.

Some fish in the midnight zone use taste and smell to navigate the waters. They use something known as magnetoception and chemoreception to detect taste and smell in the water to go to and from.

There is one other way a fish can see in the dark, ampullae of Lorenzini. This is a special sensory organ, which will allow a fish to sense the electric fields in the water to navigate. Sharks and rays are a type of fish that is known for flexing this organ.

One might wonder, does light even matter in the deep blue trenches? Let’s see.

The Long Answer

Simply put, a fish can and cannot visually see the water. At this point, you probably think I have lost my mind, but allow me to explain. There are four types of fishes, which have a different vision as we go deeper into the waters;

  1. Epipelagic
  2. Mesopelagic
  3. Bathypelagic
  4. The Deep Sea

The Epipelagic Zone

Or, in other words, the sunlight zone. The epipelagic zone refers to the 200 meters of water from the surface. This is the area where you can find fish that can see both in and out of the water. A surface-level fish uses its vision for hunting, and the latter uses it to escape.

The Mesopelagic Zone

In the darker part of the sea, where little light reaches, say hello to the twilight zone. The mesopelagic zone spans below the ocean between 200 to 1000 meters. Here, you will find fish with wide eyes and big lenses that heightens their sensitivity to light. They have a sideways vision that gives them terminal vision similar to the bigeye tuna fish.

The Bathypelagic Zone

Following the twilight zone, we enter the midnight zone, where human vision is 0.0 meter. So, how can a fish navigate in this pitch-black environment? Well, in the bathypelagic zone, a fish can sense the water and objects in their surroundings. Believe it or not, the waters are a noisy place, and every fish, the ones we know of, are born with a natural skill called lateral line that allows them to keep swimming in darkness.

The Deep Sea

Below the bathypelagic zone, we enter a different part of the deep sea. Ranging from 4000 to 6000 meters in the waters, we are in the abyssopelagic zone – also known as the abyss. Here, the conditions are similar to that of the midnight zone. As a result of which, they rely on the same lateral line as their vision. The majority of the fish in this zone are blind. Going further down, we enter humanity’s last explored oceanic trenches; Hadalpelagic Zone. It was named after hades, the greek god of the underworld.

Did you know? More people have been to the moon than the hadalpelagic zone.

How Does a Fish See Light in Water?

Light is made of waves, of which humans can see a very small part. The colors we can and can’t see are determined by wavelengths of light. Compared to us, a fish can see many colors that are beyond our visible spectrum.

Do you recall the low intensity and different colors when a luminescent light hits the surface of the water? This change in the way of light that hits you inside water is called attenuation. The light inside water scatters like a smog.

Then you have the absorption of the light, which could affect how far the light scatters. The absorption of light also depends on the color of the light. Colors that have longer wavelengths reach farther than the shorter wavelength colors. For instance, the color red has a wavelength between 700 to 635 nm, will reach farther than violet, which has a 380 wavelength.

Absorption of light can depend on various things such as heat and chemical. But all you should know is that the majority of light is absorbed about 10 feet into the water. For a fish swimming at the surface level will perceive light as a fly to a human. As you get deeper, the light gets dimmer until it becomes bluish, and eventually, black as the night.

Interestingly, the light is absorbed in the same rate in a horizontal direction. So, that means you won’t be able to see a bioluminescent fish until you are a few feet close to it. An attenuated color will appear gray or black, and fluorescent colors just behave differently (read: learn more about fluorescent colors ahead!). Now, in the oceanic trenches, if a fish wants to see a color, it can use a special reflective layer called tapetum lucidum. Light has to hit the source of light with the same color and in the same direction. If you ever find a fish with glowing eyes, they are using their reflective layer in the eye to improve their night vision.

At a certain point in the ocean, say 100 feet down, the only visible colors are shades of blue because every other color will just appear blackish. The color blue has higher photon energy. The color blue’s ability to penetrate so far into the waters might be why it appears blue to us from the surface.

So, that is how a fish would perceive color in water. It all comes down to the depth of the water and the distance of the fish from the light source. The visibility of the light in water also depends on the clarity of the water.

The Light That Only Fish Can See

Polarized light is different from normal light, but humans can’t tell – we don’t have the natural ability to differentiate between the two. While normal light spreads everywhere, polarized light exists in one plane. What is polarized light? It is the light that reflects from a metal surface or water. We are yet to fully understand why a fish is able to see polarized light, but there are some theories.

One theory suggests a fish can see this type of light because it helps them migrate. A baitfish, for example, has scales with a reflective surface. The other theory is that it helps them find prey. This theory suggests that fish can detect polarized light from afar.

If we keep this theory in mind, we could get a polarizing bait to attract more fishes. Bear fur could be a good option for bait – they have a nice reflective surface. If this theory holds up, we might see a rise in the usage of reflective surface flies and lures.

Fluorescent Light

Fluorescent colors is an umbrella term for extremely bright colors. This color is a popular choice amongst fishermen because it helps them catch more fish. According to the rumor mill, these colors can be seen by the fish from a long distance away. When a fluorescent light is exposed to light with short a wavelength, it appears brighter. Alternatively, when it is exposed to light with a long wavelength, it will get dimmer.

It Has Vision, Sure. But, What Does My Fish See?

Scientists have been trying to figure this one out by testing a fish with how it responds to images. There are far too many complications and generalizations, but the truth is every breed of fish probably has different capabilities. A parrot can’t see like a hawk, even though they are at their core, a bird. Similarly, we can’t judge how a free fish acts by observing a fish in a laboratory, as we can’t expect a free bird to continue flying around in a cage.

Nevertheless, keeping that in mind, according to the research done, a fish proves to have the ability to detect motion and colors. The contrast-detection ability has been a big revelation. So, if a fish wants to recognize a color, there has to be some level of light. The fish’s ability to detect specific colors is something that may vary from one fish to the other.

More than its vision, a fish tend to rely on lateral lines. It uses their sense of smell and sense of vibrations to prey on other fishes. Once it has detected the prey through lateral lines, the fish uses its vision for the final attack. Though a smaller fish is nearsighted, the larger lethal fish like a shark is believed to be farsighted.

Here is a fascinating fact; did you know an inshore fish has better color vision compared to its offshore counterparts. I presume this is probably due to the fact that an inshore fish is exposed to a larger variety of colors than the offshore fish, which can only detect black and white.

Does It Prefer a Color? Scientists and anglers have struggled to find the answer to whether or not a fish prefers a specific color. Inside the water, a color’s contrast changes depending on the time of day, the deep sea level, water’s clarity, even the time of the year. To answer the question of whether a fish can see a specific color or not, there need to be more scientific experiments.

Understanding The Biology Of It All

The eyes of a fish are developed like any other mammal’s eye. However, there are a few characteristics that help it stand out. For humans, if we try to see an object under the sea without wearing any goggles, it will appear blurry. A fish can see the object move back and forth to avoid seeing a blurry image.

A fish may not have eyelids, but it has rods and cones that can help them adjust to the intensity of light. When the light is too intense, the rods and cones arrange themselves to feel the sunlight less. In case you were wondering, rods and cones make up the photoreceptor cells, which are responsible for creating an image.

There are four types of cones, all of which give fish the natural ability to survive. For instance, one of the cones gives a fish the ability to see ultraviolet light, which helps them hunt for food such as plankton.

The reflected light goes into the cornea, where the rods and cells convert the light to an electrical impulse. This electrical impulse goes into the brain to produce a clear image. Ultimately, what a fish sees, and how they see it, comes down to the habitat of the fish.

Some other interesting facts that you might like to know about the fish’s eyes;

  • There are some fish which have eyes as a larva, but not as an adult. Alternatively, there might be a fish that has eyes in adulthood, but not as a larva.
  • A fish, such as an eel, changes its eyes during migration. An eel’s eyes’ lens and cones will both increase during migration.
  • While there are fish with rods and no cones, there are others that have cones and no rods.
  • In regards to darkness, a fish tends to have more sensitive cones and stronger rods.

How To Manage Light in a Fish Tank

In general, you should keep the light on in the fish tank for 12 hours. However, you need to make sure that every fish gets the necessary amount of light. This requirement may change from one fish to the other. What happens if a fish doesn’t get enough light? They might become physically inactive, and there is a chance the fish will lose their color. (read: this is for surface level pet fish, not those that you find in the deep trenches)

To avoid any health problems, I would encourage you to keep the light open for as long as the fish needs. Now, this doesn’t mean you should leave the light open for the entire day. If you never close the light, the tank will fill up with algae, and it will also confuse your fish about the time of day. Closing the light off timely, helps them get a better sense of when to sleep.

Do they sleep?

Have you ever wondered if the fish ever sleep? I know the thought has come across my mind a couple of times. The answer is yes, fish sleep. In fact, you might have noticed them sleeping on more than one occasion. I’m talking about those instances where you catch the fish floating mindlessly – guess what they are doing? Sleeping! Simply put, sleeping for a fish is akin to human daydreaming. Their brain is functioning at a low level, and they can still sense their environment.

Bonus fact: There is a fish that covers itself in a jelly before sleeping. 

Can the fish in a tank see the surface?

Yes and no. Do you recall how light from a flashlight appears in the roof? The closer you put it, the clearer and smaller it appears. The farther it is, the light is more spread out and unclear. Similarly, fishes have a vague but large picture of the surface from the bottom of the fish tank. However, as they get nearer to the surface, the picture gets clearer but smaller.

Fishing in the Deep Blue

This section is a guide on how you can use all this information to fish in the deep blue. I got you covered, ranging from the colors to the type of bait you should use, this will help that bucket of fish overflow. If you are heading out to fish, here are some tips to keep in mind regarding the fly and the bait;

  • Change the color of the fly at different depths of the water. For a surface level fish, you could experiment with different colors like red, blue, and so forth.
  • You could also try matching the color of the fly with the color of the bait when it’s inside the water.
  • Keeping mind that black is the most visible color, I would suggest you pick a dark-colored bait over the light-colored one. The darker color could bring a better contrast.
  • Fishing in deep water, remember that noise and motion are more important than color. Why? The fish in deep water have a higher sense of literal line as opposed to vision. Who needs sight when you live in a blinding black atmosphere?
  • For pairs of color, I would recommend fluorescent colors like chartreuse and white, or red and white. These combinations are an angler’s popular pick.

Friendly tip: If the water is dirty, use a higher contrast fly. Similarly, decrease the contrast if you are fishing in clear waters. When you aren’t going for something bright, my personal pick is pure white.

Fishing at Night

The perfect time of the day to fish is at night. The netters are gone, and at that chilly time, it is easier to catch the fish. Let’s be honest, sitting under the hot yellow sun isn’t easy. Also, there are fewer fishermen out; more fish for yooou! Plus, at night, some fish tend to swim close to the surface. If you do decide to try night fishing, I’d recommend heading out during the summers – tis’ the merry season of fishing. Additionally, when you are out there, remember to keep moving that rod; a fish has a stronger sense of motion and vibration when it isn’t using vision.

Bonus note: Use dark-colored chatter bait to attract the fish at night.

I will caution you that it is dangerous to go out on your own if you don’t know how to navigate the water at night. This won’t be easy for a newbie, but once you get the hang of it, you will catch the big fish more easily than you could during the day.

Related Questions

What colors do fish see at night?

The colors in water are actually different from the ones we see on the surface. Inside the water, the colors may change depending on the wavelength. Interestingly, a fish is capable of seeing colors that the human eye cannot, such as ultraviolet.

Can a fish see water?

A fish cannot see water, because it is constantly exposed to this environment since a larva. These little guys can neither taste, hear, or smell the water because of the same reason.

Can fish see lures at night?

Yes! They can see lures at night. A fish that adapts to hunting is capable of spotting a lure at night. Though a light-colored lure should grab their attention, I would recommend using something darker because it is easier for the fish to identify a dark-colored fish.

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