Last Updated on: 24th May 2021, 07:59 pm
A fish’s eyes are complex and sophisticated. That’s because underwater conditions are unpredictable. Fish must be able to find food, hunt, and escape predators, so their vision is crucial to their survival.
Fish have good close-up vision underwater, but can’t see well from a distance. They can see things underwater up to 1 meter away clearly, but anything more than that becomes blurry. Fish also have blind spots. A fish’s underwater vision is mostly connected to the water’s conditions. If the water’s clear, they’ll see better than in murky water. Fish can also see color and UV light.
Over 30,000 fish species are living in different seas, oceans, and waters. As a result, they all have various visual capabilities.
How Do Fish See Underwater?
A fish’s eyes don’t function that differently from a mammal’s. When reflected light enters through the cornea, it moves through the pupil to get to the retina.
Then, either the cone or rod cells convert the light into electrical pulses. The optic nerves pass these pulses to the brain, producing an image. A fish’s eyes contain the following components:
- Cornea. This is a transparent outer layer that protects the eye against damage and debris.
- Lens. This focuses the light received by the eye and forms the image.
- Iris. This adjusts light levels and controls the amount of light that reaches the retina.
- Retina. This lines the back of the eye and contains light-sensitive cells.
Though these components are similar to our eyes, there are many noticeable differences that allow fish to see underwater.
Can Fish See Clearly Underwater?
While a fish’s eyes function in a similar way to ours, they’re built to adapt to their environment.
For example, most mammals have eyes that are designed to function when exposed to air. In comparison, a fish’s eyes are designed to work underwater without goggles. That’s because they have almost-spherical, hard lenses, allowing them to see everything up to 1 meter away clearly.
Fish also have different muscle arrangements and tissues that are close in density to the water around them. Similarly, there’s little difference between a fish’s cornea and the sea water’s density, meaning there’s not much refraction (bending of light). So, the lens does most of the focusing.
As described by the Indian Journal of Ophthalmology, some fish also have a nictitating membrane, which is a protective film over their eyes. It helps them see more clearly while moistening the eye. Fish that don’t have this have an extension of the skin that covers parts of the eyes.
Fish can’t see detail very well, but they can see movement and contrast. That being said, how well a fish can actually see underwater depends on:
- Water clarity
- Underwater light penetration
- Wind action
- Suspended particles
- The angle of the sun
The better the water’s conditions, the more clearly the fish can see.
How Far Can Fish See?
As already explained, fish can see for up to a meter underwater. However, that’s about as far as they can see clearly. Some fish can’t even see this much. It depends on the species and whereabouts in the world they live.
Fish have been historically described as being near-sighted. That’s because they can see objects more clearly when they’re closer to their eyes. In fact, fish can focus better on things that are closer to them than humans can.
In order to look further away, they adjust their focus by moving the lens closer to the retina. While they still can’t see far, they don’t usually need to. That’s because the water’s conditions aren’t good enough for clear faraway vision. Even if fish did have good long-sighted vision, they wouldn’t be able to see anything.
Though fish aren’t thought to be able to see that far, they have a broad panoramic view because of their side-facing eyes. Fisheye camera lenses mimic this unique feature.
This allows fish to see more of what’s going on around them instead of what’s directly in front of them.
Can Fish See Color?
Fish can see more colors than us because they have receptors for red, green, and blue light. And because a fish’s eyes also contain rod and cone cells on their retina, they can see color as well as light, dark, and grey shades.
The ability to see colors allows fish to locate colorful prey in deep waters. Fishermen exploit this ability by using colorful bait to reel them in.
However, fish need enough light to be able to see color. As a result, fish living in shallower waters can see color more clearly. That’s because fish live closer to the surface, receiving more light.
On the other hand, sea fish that live deep underwater have larger eyes, allowing them to detect more light in their darker habitats. Then, there are some fish that have tiny eyes. They rarely see color. Neither do fish living in waters without any light at all. Color may be present, but it doesn’t show because of the lack of light.
Water depth affects colors. The deeper the ocean gets, the less likely color is to show. Again, that’s because there’s not enough light. The different water depths include:
- The epipelagic zone (the sunlight zone) – surface to 656 feet
- The mesopelagic zone (the twilight zone) – 656 to 3,281 feet
- The bathypelagic zone (the midnight zone) – 3,281 to 13,124 feet
- The abyssopelagic zone (the abyssal zone) – 13,124 to 19,686 feet
- The hadalpelagic zone (the deep trenches) – 19,686 to 35,797 feet
The light that penetrates the mesopelagic zone is very faint. By the time fish get to the bathypelagic zone, light barely exists at all. As a result, their perception of color changes. The only visible light is produced by the creatures that live there.
Can Fish See Ultraviolet Light?
While ultraviolet light is invisible to us, many fish can see. As described by Live Science, UV light is a type of electromagnetic radiation that comes from the sun as short wavelength, high-frequency energy.
When it comes to evolution, Darwin’s theory is that animals lose things over time they no longer have use for. For example, fish that don’t use their eyes will eventually evolve to have no eyes. Many deepwater fish live deep underground where it’s pitch black, but they still have their eyes. This is likely because they can see UV light.
Ultraviolet light penetrates further into the water than visible light, meaning fish living deep in the water’s depths are more likely to see it. However, it’s also visible in shallow water.
Some fish, such as the juvenile brown trout, rely on their ultraviolet vision to detect zooplankton to eat.
UV light also plays a significant part in mate selection, which is why some fish can see it. For example, Vision Research explains how ultraviolet light is vital for some cichlid fish.
Cichlids naturally breed in shallow waters with UV light penetration. Because male African cichlids are blue, their scales are reflective in UV light. Female cichlids use visual clues to find a suitable mate of their species. As a result, UV light is helpful for sexual reproduction.
In another example that shows fish can see UV light, Current Biology found that the Ambon damselfish can see UV patterns on other fish. They can also detect the lack of ultraviolet lines on other fish species. This means they’re able to use UV lights to distinguish their own species from similar-looking fish. Ultraviolet light can also be related to:
- Communication behaviors
- Reproductive fitness
- Mate selection
- Send sexual signals
- Hide from predators
Can Fish See In Darkness?
A fish’s retina captures larger light frequencies, making its vision clearer when it’s dark. However, similar to seeing color, fish can see better at night when the water’s clear. If it’s muddy or murky, they won’t see well at all.
Furthermore, fish don’t just use their vision to see when it’s dark. They use their sensory organs to detect movement and vibrations in the tank.
Similarly, fish are most likely to sleep when it’s dark. At night, they reduce their brain activity by half and stop moving as much as they do when it’s light.
Fish Vision Vs. Human Vision
We’ve already mentioned many of the similarities between human and fish eyes, of which there are surprisingly many. But there are also many differences. These include:
- Fish have no lachrymal glands (tear ducts). That’s because living in water, they have no use for them.
- Fish don’t have eyelids. Instead, they rely on a nictitating membrane or covering of skin to remove debris from the eyes and protect them while they’re feeding.
- Unlike ours, a fish’s lens is purely spherical and has a higher refractive index than ours.
- A fish’s lens is fixed in shape. When fish want to focus on something nearer or further away, they move their lens backward and forward. We change the shape of the lens.
- Fish can see a wider spectrum of colors that we can’t.
- Fish have better peripheral vision than we do.
Fish Eyesight Facts
Fish eyes come in all shapes and sizes, making them unique from species to species. As a result, there are plenty of interesting fish eye facts to discover, including:
Fish Can Recognize Faces
A study by the University of Oxford discovered that fish can recognize and distinguish between human faces with a high degree of accuracy. Even though fish lack the visual cortex that primates have, they have excellent optical discrimination properties, which are propelled by their advanced eyesight.
To test this, researchers presented archerfish with two images of different human faces. They were then trained to choose one using their ability to spit jets. The researchers then showed them the learned face alongside a series of new images. They achieved an 81% success rate in the first test and 86% in the second experiment.
As a result, even though they lack the part of their brain that allows humans to recognize faces, they possess impressive visual behaviors that work in a similar way. This is even more incredible when you consider that fish also have a water barrier to contend with.
Fish See Out Of The Side Of Their Head
Fish don’t have necks, so they can’t turn their necks to see what’s around them. Instead, their heads protrude out of the sides of their head. Similarly, each eye can move independently. As a result, each eye has a 180-degree view of its surroundings.
This is an evolutionary adaption that gives fish a wider vision spectrum. It allows them to see predators and find food. Prey fish are more likely to have eyes on the sides of their head, enabling them to flee.
In comparison, predator fish’s eyes are located more towards the front of their head, giving them greater depth perception and binocular vision to see their prey more clearly.
Some Fish Have Telescopic Eyes
Some fish have round, protruding eyes that look like telescopes on the side of their heads. The telescopic eyes fish, which is a type of goldfish, is a prime example. Similarly, demekin, eyes of dragon, and moors fish also have this feature.
In most telescopic fish, their eye stalks can protrude out as far as 19 to 20 cm. They start to stick out when the fish is around 6 months old.
However, when aquarium conditions aren’t suitable, their eyes are prone to bacterial and fungal infections, as well as parasites and protozoa. The tank also can’t have any decorations or plants with protruding points, as they can injure the eyes.
Despite common misconceptions, fish can see well underwater – at least up to a meter away. That means in a standard aquarium, they’re able to see much of what’s going on around them. They might even be able to recognize who you are, even though they’re underwater.