When you go to bed at night and turn off all the lights, you turn them off for your fish too. After turning out the light, you may have wondered to yourself: can my fish see in the dark?
The short answer is yes! All fish are able to see in the dark to some extent.
Some fish are better able to see in the dark than others. Below, we’ll talk about how fish can see in the dark, just how well they can see in the dark, and which fish species see the best (and worst) in the dark!
How Do Fish See In the Dark?
So fish can see in the dark, but how do they do it?
Fish are able to see in the dark for a few different reasons. The first is that their eyes are made differently than ours, so they can see more than we can.
For example, fish have a very dense, spherical lens that gives them better peripheral vision. This increased scope of vision helps let more light into their eyes, so they can see well in low-light environments. (*)
You may have heard of a “fisheye lens” for a camera. This lens gives you a greater periphery when taking a photo because it’s shaped like the eye of a fish.
Some fish species also have a night vision superpower. That superpower is called a chromophore.
Big word, We know. Stay with us.
The chromophore is a chemical compound that can join with a protein called opsin. When combined, they magically create a visual pigment in the eye. (*)
When light hits this pigment, it sends a signal to the brain. This is how fish see!
The thing is, there isn’t just one type of chromophore. The chromophore is made with either:
- Vitamin A
- Vitamin B
Some fish, like salmon, are able to make both types of chromophores and switch between them. This gives them night vision!
So, not only do fish have better-shaped eyes when it comes to seeing in the dark, some of them have chemicals that help them do it too.
What Do Fish See In the Dark?
You may be wondering: what do fish even need to see in the dark? The answer is, well, lots.
Seeing in the dark is important for fish because they need to be able to see:
- Other fish
- Open paths
Though most fish rest at night and don’t do much in the way of hunting, a hungry fish may take advantage in the dark and snatch some yummy prey.
The most important thing fish need to see in the dark, though, is predators. An unsuspecting fish that can’t see or sense danger in its presence is in for a bad time.
Being able to see danger in the dark gives fish a chance to escape to safety or otherwise defend themselves or their homes.
Fish also need to see other fish. Whether finding a mate or defending territory, fish need to see at all times where their school or enemies are.
Finally, fish certainly need to see where they’re going. Though most fish rest at night and in the dark, they may still need to travel to a specific place to rest.
Imagine trying to navigate your house at night after you’ve turned the lights off. You may have a general sense of direction as to where your bedroom is, but you suddenly won’t be able to see any obstacles left in your path.
That one lego that your kid left out is suddenly your biggest foe.
In the same way, fish can’t see in the dark, they’ll have a hard time finding their way to a safe resting place, and can even accidentally hurt themselves by bumping into objects in the water.
Night vision is vital to keeping fish safe and healthy, especially in the wild.
Which Fish Species See Best In the Dark?
Though all fish have a sense of “seeing” around them in the water, some fish have better vision than others. In particular, some of these strong-eyed fish include:
Though the only ones on this list that you may have at your home aquarium are walleyes and Oscars (and maybe some small breed sharks, if you have a big enough setup!), all of the fish on this list are adept with incredible night vision to keep them safe in the wild.
Walleyes make an excellent catch for fishermen, but some advanced aquarium keepers may choose to raise them as pets.
However, these fish are known for more than how they taste. They actually have excellent vision.
Research says that walleyes have excellent vision in both light and dark. In light, they actually have a greater color range than some fish, and see similarly to humans that are colorblind for blue and red.
In the dark, they have extremely photoreceptive eyes that use even the smallest bits of light to see clearly through the water. While they can see, their prey don’t have as good eyesight, giving them a “leg up” over them.
As a result, walleyes are more active at night. This is why fishermen try to catch them after dusk! (*)
If you raise walleyes, be assured you won’t have any issues when it comes to their vision.
Salmon are known for their highly advanced vision. As we mentioned before, salmon are one of the fish that alternate using Vitamin A and Vitamin B to produce two types of chromophores.
They then use these chromophores as needed to see in both light and darkness. This helps them avoid predators such as bears so they can swim to safety any time of day.
Salmon also has an enzyme called Cyp27c1 (who even comes up with these names?) that they use to produce natural night vision. Enzymes are proteins that make chemical reactions happen in living things. (*)
When salmon enter murky water to mate or flee, they can “switch on” this enzyme to see better in deeper darkness.
They’re basically the super-spies of the water.
Sharks are known for their intelligence and strength, but did you know they’re also known for great vision?
Scientists say a shark’s eyesight is similar to humans, but is ten times stronger underwater than ours. This makes sense, since… They live there and we don’t.
Sharks are interesting because they have a tapetum lucidum like many vertebrates, which is a reflective tissue layer located behind the retina.
If you’ve ever seen your cat’s or dog’s eyes glow in the dark when you shine a light at them, congrats! That’s their tapetum lucidum, which means they have something in common with a shark.
This layer reflects light back to the retina to get a clearer image. By letting the light hit the retina twice, there’s a smaller chance the shark will miss anything in its sight.
This means greater hunting and defense abilities in murky waters, a definite benefit for them.
Can Any Fish Not See In the Dark?
This answer’s a bit more complicated. It depends on how you define “see.”
Fish that live in the deep ocean where there’s no light, for example, don’t need to “see” the same way we do.
Instead, they have special organs that are extremely sensitive to changes in pressure and temperature. They’re so sensitive that they can “feel” when other fish or plants are near them – super cool! (*)
Since that’s how they can tell what’s in front of them or around them (and how they find food and escape predators!) you could consider that their ability to “see.”
However, they also have the ability to see slightly with their eyes, by using receptors that can see bioluminescent shrimp or plankton. Bioluminescent means these creatures glow, and even the faint light is enough for them to see.
Aquarium fish have some of those pressure sensors too. Even though they can use their eyes to see a bit in the dark, they use pressure sensors to really give them a full picture of their surroundings.
Fish that live where any amount of light enters the water, have at least a weak ability to see in the dark similar to other animals. So we assure you, you don’t have to worry about blinding your fish when you put him to bed at night!
Now You See!
When you turn out your fish’s light at night, you no longer have to be afraid you’re leaving them in pitch darkness. Even without their tank light, they can definitely see their way around the tank.
Plus, if you have fish such as Walleyes or Oscars, they can see even better than other species. Even so, they definitely appreciate the lights out at night so they can rest!
If you’re new to raising fish, we advise you to turn out your fish’s light every night on a regular schedule. This gives them their needed rest so they’re bright-eyed and active during the day.
If you learned something new from this article, feel free to leave a comment below. If you have more questions or ideas for future articles, let us know and we might write on it!