Do fish use their eyes? How do they see the world?

A fish’s eyes are quite similar to a mammals’ eye – but that doesn’t mean they see like a mammal does. Why? Because a mammal can’t really see underwater.

This brings us to the question, how does a fish use their eyes? More importantly, how does this squirmy marine life see the world? I embarked on a mission to answer these curious questions. To my surprise, I found some really interesting facts about our friends that live in the ocean.

What did I find out? How in the world does a fish see? Read ahead and learn all you need to know about these answers.

How Well Can Fish See Colors (Video)

The Way It Works

Fish eyes may be similar to the mammal’s eye in many ways, but there is one huge difference that changes everything. Fishes have a round lens that allows them to view things a bit differently. They have to move their lens back and forth to see.

Here is what you need to know, a fish is normally nearsighted. This means it can focus on objects more clearly when it is nearer. We can see objects that are placed far away. When you cast a fish line, it won’t really notice it from afar. However, this doesn’t necessarily mean that a fish can never see an object far from them. There are some cases when a fish can manage to spot an object. How? We will dig into this later.

The fish’s nearsightedness isn’t the only thing that is different from how we see things. One unmissable difference is that their eyes are sideways. This mind-boggling thing is one of the main reasons why I wonder about how a fish sees. So, why does a fish have eyes on the side? The simple answer is; it helps them spot any predator or prey.

This is how a fish sees, but what they see can depend on many things, such as water depth.

Water Depth

The depth of the water plays a great role in how a fish sees underwater. Normally, a fish’s eyes use the light rays bending inside the water to see. Their eyes are made with rod cells and cones cells that use this light ray and colors to create an image. Albeit, what a fish can see is usually very blurry.

As you get deeper into the ocean trenches, it gets darker. At the bottom of the ocean, it is pitch black. By the time you swim into the midnight zone, you can’t see anything. The light can only reach a certain distance in the water. When your fish is swimming in a dark blue ocean, it stops relying on its vision. The rod cells and cone cells are essentially useless here.

Fish swimming in pitch black stop relying on vision, and start relying on smell and taste. Yes, smell and taste. It uses these two senses to make their way around the darkness. Fish at the surface also use these senses during the night. It has ears to hear, but it doesn’t hear all that well.

Lateral Lines

Though smell and taste are helpful, a fish mainly relies on lateral lines to go about its day. What are lateral lines? This is a fish’s natural ability to sense movements, pressure, and vibration in the surrounding. So, a fish can later use lateral lines to target its prey and to also escape predators. Lateral lines also help fish move around the water by sensing how the water is moving around them.

Scientists are still looking into this, but there is a possibility that fish use something called electromagnetic fields too. Similar to lateral lines, it senses these electromagnetic fields to detect the fish near them.

Can Fish See Color?

Fish can see, but do they see color? Yes and no. The fish swimming near the surface is exposed to more light and colors. Their ability to detect colors is helpful in finding food and identifying fishes and objects that are nearby.

The deeper you go into the ocean, the colors begin to change due to the less light. So, when it gets darker and darker to the point where you can’t see anything. So, does it really matter if they have color vision? Nope.

At the bottom of the ocean, as a human, you won’t be able to see anyone or anything even if it is standing right in front of you. Like a fish, you will be able to see anything that is colored black or blue, because these are the only two colors with the wavelength that can reach this far.

While swimming around the darker parts of the ocean, a fish stops relying on its vision. They start depending on their other senses and lateral lines. Interestingly, as you go deeper into the ocean, the number of colors a fish can see begins to drop. Some new information has come up that the fish on the deep end have better rod cells that can detect colors.

UV Light

A fish is naturally capable of seeing colors way better than humans. Humans can see colors at a wavelength between 400 to 700 nm. The human eye’s rod cells and cone cells have three color palettes; red, green, and blue. Our friendly marine neighbors, on the other hand, can not only see those three colors, but it can also detect ultraviolet light (read: UV light). They can see UV light thanks to their ability to see colors on a shorter wavelength, which is 10 nm.

If you are a fisherman, you can use the UV colored lures to catch more fishes. Scientists believe that the UV lures are easier for the fish to detect; it stands out from the background and attracts the fishes. Normally, the UV light reflects off a fish and plants that help the fish find its food.

Humans Can See Water, Can Fish See Air

If we can see water but not air, does that mean fish see air but not water? Nope. Fish cannot see air. However, if you find it consoling, fish don’t exactly see water. Simply put, a fish uses its brainpower to focus on its other senses that are needed to survive. They basically filter out the water.

Bonus point: Humans filter out air to focus on the other body functions. 

There are some cases when fish can see the water. For this to happen, the fish has to go through an experience that changes their perspective about water. What is this life-altering experience? It’s jumping in and out of the water. In this experience, a fish can finally see water.

To make it simpler, a fish that swims in the deeper parts of the water and refuse to come up, they’ll never be able to see the water. The surface level fish that manage to go above can see water.

How Fish See The World

A fish can see stuff, great! But how exactly do they see the world? They see it blurry. To understand this, you gotta understand how we all see a clear picture. The light in the air is dense, and it isn’t bending through anything. Underwater, its a bit different – light is scattered (it looks like a fog), and it is less dense. Inside, the light bends, and they can’t get a clear picture.

On a good day, when the water is clear and the light bends in the right way, a fish can see as far as 100 feet. This is very rare. Above the water, do you wonder how a fish sees the world? They see it as a mirrored version of the outside – everything is upside down.

Also, since a fish has its eyes on the side, it can be difficult for them to see what is in front. It can move the eyes about 30 to 45 degrees back and forth to see its surroundings. But, it is difficult to see what is in front. At the end of the day, it doesn’t matter much because it relies on their lateral lines.

Related Questions

Can fish see in front of them?

A fish has eyes on the side, so I naturally come to this question. Is a fish able to see the things in front of it? Like a human, a fish’s eyes move together. So, when it focuses forward, a fish can get a clear picture of the object. This is where you get a binocular vision.

Can fish see UV light?

A fish’s eyes have rod cells and cone cells, which rely on their color vision and UV light. Unlike humans, fishes have the ability to detect UV lights. They can also detect polarized light too.

How far can fish see?

If a fish was out swimming on a clear day with the clearest waterway in front of them, a fish could see as far as to 100 feet. On the dirtier side, it won’t be able to see past a few inches. On a normal day though, it can see as far as 6 inches. In an unusual situation, where the light isn’t scattered or absorbed into the water, a fish can clearly see the objects.

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