Can Fish See In The Dark? Do All Fish Have Night Vision?

Deep sea fish species have eyes suited to dark environments but can all species of fish see in the dark?

Most fish can see in the dark due to evolved cone cells in fish eyes. But still, you must turn off the aquarium light for at least 12 hours to give fish time to rest.

Some fish can see in the dark better than others because of differences in the number of cones present in each fish species. The vision of fish is different because light reflects differently in aquatic environments than it does for humans. The amount of night vision fish have and colors they are able to see depend heavily on the depth at which fish reside. The concept of wavelength comes in handy in understanding what colors fish are able to see. For instance, blue and green colors have longer wavelengths and therefore deep underwater fish appear to be blue, green, and black, masking them from predators.

After reading all about the vision of fish that helps them see in the dark, how they detect movement in the dark, and the effect of pressure changes on the way fish see, do read about how often to feed fish and why do fish jump.

What happens if you leave a fish in the dark?

At first, an aquarium fish will think that it is nighttime and go to sleep. It is important to ensure that fish stay in the light for at least 10 hours each day so that they can swim around, eat and play. However, they are unable to sleep properly unless it is dark. Fish should never be left in the dark for extended periods of time; this is especially true for fish that live in tanks or shallow water bodies.

Chromatophores are cells present within bodies of most fish. These cells are responsible for the pigmentation of the fish. All the wonderful bright colors that you see on fish are formed because these cells produce colors in the presence of light. If these cells are deprived of light for a longer period of time, they will stop producing colors. In many cases, it has been found that there is a decrease in immunity levels caused after leaving fish in the darkness. This makes them prone to illnesses leading to their deaths. Also, experts suggest that fish should never be kept in total darkness. This increases stress levels in fish when the aquarium light is suddenly switched on. Always leave a low light turned on for them.

Are fish scared of the dark?

Can fish see in the dark? As per science, fish are not afraid of the dark.

Different fish have different habitats and requirements. Deep underwater fish are surrounded by darkness for most of their lives. Aquarium fish, however, experience both light and dark. When tank lights are suddenly switched on after a period of darkness, fish get startled. The same is true when you switch off aquarium lights suddenly and there is total darkness. This is because of the sudden nature of the change.

A dim light is preferable during the transition. Switching on the room’s light or removing curtains before plugging in tank lights has proved to be effective. This way fish get adjusted to the dim light and then have no trouble adjusting to brighter light. The reverse can be done while switching lights off. First switch on the dim light and only after around 30 minutes or so submit fish into total darkness. Blue light is also helpful in this transition. Although blue light prevents total darkness, it is not an ideal setting for fish to resume eating their food. Therefore this light is better used to help in the transition period. Fish need 12 hours of light on average. It is important to maintain a day and night cycle for them just like human beings and other living organisms. They need 12 hours of dormant state to ensure that they are playful the next day. Without these 12 hours, they will remain lethargic and tired. Different fish species have good vision in the dark and detect movement with the help of cone cells in fish eyes. Did you know that fish sleep with their eyes open?

How do fish see underwater at night?

How do fish see in the dark when the amount of light that reaches deep waters of an ocean is nearly none? At night, there is total darkness all around fish. Whether fish live deep underwater or towards the surface of the ocean, it has been found that these animals are more likely to feel their surroundings than see them.

Fish have sensory organs along their sides, known as lateral lines. This is present all along the body and is of great assistance in sensing animals around it by gauging pressure changes in water. They are able to detect movements in low light conditions and in darkness. Some fish species such as sharks and electric eels are able to detect movements through electric fields that are generated from each animal.

Lateral lines assist fish to not only detect movements but also help them navigate and move through dark waters and even muddy waters. Aquarium fish can understand each other's positions by lateral lines detecting changes in pressure as well as through sound waves generated during communication. In low light conditions, most aquarium fish are able to see bits and pieces. They have certain levels of night vision which assists them in detecting movement of their surroundings but they mostly rely on their sensory organs.

Do all fish have night vision?

Although fish do not have eyelids, they have a protective layer on their eyes which enables them to see clearly underwater. Just like humans, fish also have rods and cones present in their retinas. Like humans, sharks can see colors. Because they have eyes located on both sides of their head, there is a blind spot of every fish whenever it is swimming or eating.

Due to the presence of rods and cones, all fish have a certain amount of night vision. Fish can see some of its surroundings because of cones present in its retina. However, this varies according to the natural habitat of fish. Some fish, like walleyes, have good night vision compared to other fish species. Fish who cannot see well navigate their movements with the help of their sensory organs. Being predators, they use their sensory organs to smell, see and hear the sound of their prey. Those with night vision are able to survive well in the world of underwater environments. They are able to distinguish between predators and prey with much more efficiency. Humans have chemicals in their systems which is why we are able to see so many colors. Fish also have these chemicals. Additionally, fish can see the ultraviolet spectrum.

How do fish swim or find food in the dark?

Fish are able to swim and find food in the dark because they have lateral sensory organs which indicate changes in water pressure. This enables them to move ahead and also indicates what lies ahead of them. They have spherical lenses, providing them with better peripheral vision than that of humans. Sensory organs allow fish to feel vibrations around them. This indicates whether something around them is moving or not. Sensory inputs also enable fish to understand whether a predator or prey is approaching without having to look. Some nocturnal fish, like puffers and gobies, become highly active at night and tend to eat food in total darkness.

Fish are able to find food in the dark with the help of their sensory organs. Those fish species who do not have night vision or have unclear night vision effectively use their lateral sensory organs and navigate through the water. They are able to smell food and even hear it. When food comes towards them, there are changes in water pressure. The lateral sensory organs detect this change and evaluate the substance causing the change before moving towards it. Most tank/aquarium fish do not have night vision and prefer to eat when there is light, even if it is dim light. They detect vibrations in the water through their specialized cells called lateral lines or neuromasts. Some fish species like angler fish and barracudina have special adaptations in their bodies because they live at extreme depths of water. Such species tend to rely heavily on their lateral lines and other sensory organs.

Sometimes they may also generate light of their own for assistance as natural light does not reach deep underwater. Fish with round lenses and big eyes are able to see better at night than other fish species because they use the reflected light from the moon and stars. But this is only possible for fish species that live closer to the surface of the water.  Aquarium fishes switch to a dormant state in the dark which allows them to navigate to the surface without bumping into each other while they rest.

Is it better to just leave the light on?

Not at all. As mentioned before, fish need 12 hours of rest which is best possible in the dark. Irrespective of the room where the fish are kept, it is important to ensure that lights are switched off. Hours spent under the light enable different fish to behave differently. For instance nocturnal fish tend to hide under rocks and remain inactive when there is light. Other fish species, on the other hand, eat, move around and play with one another. If fish do not get their set hours of sleep, they are not active. Darkness is necessary for fish to sleep peacefully. Another important reason for not keeping lights on the entire time is the formation of algae. Green algae that form on the glass and the light present in the tank increase significantly if lights are left on the whole time. Green algae, if left in the tank, tend to limit the oxygen supply of aquarium fish, leading to death. Even if the room where the tank is kept is naturally lit, cover the tank with a cloth or bedsheet to ensure that fish get their required hours of darkness and sleep.

Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for can fish see in the dark then take a look at how do fish mate or Tarakihi fish facts.