Can Fish Live in Dark? What Do They Do at Night

As an avid aquarist, one question that often piques my curiosity is, “Can fish live in dark?”

Over the years, I’ve observed that the behavior of my fish changes as the daylight fades and darkness takes over. Fish, much like many other creatures, respond to changes in their environment, and light is no exception.

Despite the lack of visual acuity in humans during darkness, many fish species thrive in such conditions, showcasing a fascinating aspect of their biology.

Indeed, fish can survive in darkness. This adaptability is largely due to their unique sensory capabilities.

Many species of fish have specialized cells called photoreceptors that enable them to see in low light conditions or even complete darkness. Additionally, fish employ other senses in the absence of light.

For instance, they use lateral line systems – a series of sensory organs present on their sides – to detect changes in water pressure and movement, enabling them to navigate and locate food in the dark.

Therefore, even though light plays a vital role in their daily routines and biological functions, fish are well-equipped to survive and operate in darkness.

How Do Fish React in the Dark?

Fish are surprisingly aware of the day and night cycles, and their innate sense of time prompts them to engage in various activities, just like any other living organism.

During the day, they are often seen swimming around, in search of food, or engaging in copulation. When the light begins to slow down its pace, signaling the onset of darkness, fish naturally ease into a more restful period.

However, if you suddenly darken their room, they might react poorly and appear confused.

To ease their stress and make life easy for them, it’s better to apply the same typical day routine by mimicking a light and dark cycle. When the tank light is put on, it signals the fish that they should be awake.

When the lights switch off, it’s an indication that they are about to sleep. Over time, this routine adapts to their environment and maximizes their time for rest and work.

An experiment conducted by Anika Bruning highlights how light delays the sexual maturation in fish.

The laboratory experiments suggested that the reproductive mechanisms in fish would likewise react to deficient levels of light.

There is a particular light-sensitive time of the year when rivers, streams, and clear lakes, the popular sources of community aquarium fish, are bathed in bright sunlight and the warm rays of rainforest weather, second to none.

In contrast, darker areas accommodate those fish that prefer to hide.

The receptivity of fish to light varies greatly depending on the species and their developmental stage. The fish eye, along with the pineal gland and certain photoreceptor cells, provides an explanation of how fish see in the dark underwater.

Eddie Waithaka

Once said that fish have rows of pressure-sensitive organs, known as lateral lines, running down each side of their body.

These lines, called neuromasts, allow the fish to sense nearby animals or pressure changes in the water column.

The structure and function of fish eyes are pretty similar to human eyes, with the significant difference being that fish lenses are spherical rather than compressed, enabling them to focus better underwater and making them better at seeing in low light conditions, whether at the bottom of a muddy lake or in the brilliant light of living sunny coral reefs.

Depending on their lifestyle, they can even perceive ultraviolet and polarized light, something humans are unable to do.

How Many Hours of Darkness Do Fish Need?

Tropical aquariums typically require at least 12 hours of darkness every day while cold-water aquariums require more.

It is generally recommended to illuminate fish tanks for 8–12 hours each day. However, fish living in aquariums need about 12-16 hours of darkness every day and need around 8-12 hours of light to thrive.

Light timers and alarms are straightforward and successful approaches for regulating a fish’s night and day cycle.

Maintaining consistent light cycles that mirror the daytime and nighttime alleviates stress and can help replicate their natural settings.

Tank placement can play a significant role and affect the success of these cycles.

If you have a basement or a room without windows where you do not want to buy and install a dedicated aquarium light, a simple solution is to put the lights in the room on a timer.

This will make the proposed day and night cycles applicable. A survey has proved that most fish lovers believe the maximum of 10 hours of light is enough, and the fish can stay in the dark throughout the rest of the day.

However, other factors need to be considered to determine a fair number of light and darkness hours for your fish species.

You have to consider what kind of fish you have, what kind of aquarium you have, the numbers and plant types in your tank and the ambient location lighting.

If you don’t have live plants in your tank, you might be able to get away with utilizing less light. On the other hand, some fish may not appreciate reduced lighting hours.

Sleep is essential for fish as it promotes improved health and illness resistance.

Algae tend to develop faster in a tank that is lighted for more hours a day, which can make the tank look unclean.

If you have natural plants in your tank, the algae may be able to outcompete a large algal bloom, which can also cause an oxygen deficiency and kill the fish.

Do Fish Need Aquarium Light?

Fish in an aquarium not only need light to be healthy and happy, but also to maintain a balanced environment in their tank.

The source of light can be an overhead lamp or a designated aquarium light, each having a distinct aesthetic impact on the fish tank.

It should be noted that fish require a break from direct light, much like humans do from regular light exposure.

Modern lights offer degrees of intensity that can be adjusted to simulate day-night cycles for fish, promoting plant growth, aiding in algae control, and enhancing water quality.

If you’re a travel enthusiast, maintaining an immaculate light schedule for your fish might seem like a potential caveat.

However, there are timers available in the market that can turn on and turn off the aquarium lights at specific times. Some modern lights even come with built-in timers for ease of use.

If you’re forced to travel and unable to procure a timer, a simple solution could be to leave the tank light off and place the aquarium in a room with windows.

By leaving the curtains open, the light of the day can suffice for the fish’s lighting needs, maintaining their day-night cycles.

Alternatively, you can also have a friend turn on and turn off the aquarium lights, but this option might not be as reliable as the other ones mentioned.

Video Guide | Do Aquarium Fish Need Light At Night

Why Sunlight Is Bad for Aquariums

Using my fish tank as an example, the idea of exposing it to direct sunlight might initially seem beneficial, but it can actually produce a detrimental impact on the flora and fauna within the aquarium.

The warmth and light from the sun can lead to an overgrowth of algae, which is not only aesthetically unpleasing but can also quickly cover the leaves of water plants.

Algae, like plants, photosynthesize and absorb nutrients from the water column. When the leaves of water plants are covered by algae, it impedes their ability to photosynthesize effectively.

While the infested plants won’t die right away, the algae impede their growth and reproduction, posing an immediate danger.

Another issue arises with the temperature of the water column. When the sun is hitting the tank directly, it can warm up faster than you’d think, especially on hot and bright days.

This increase in temperature can be more than some species can handle, leading to their respective demise. On the other hand, on days with no sun, the temperature may drop, and these fluctuations can cause stress to the fish.

Considering that many decorative fish are bred in tanks with stable temperatures, these variations can be particularly harmful.

Therefore, direct sunlight is arguably the worst source of light for a fish tank. An overhead room light could be a better alternative as it won’t change the temperature of the aquarium significantly.

However, the best option would be a dedicated aquarium light. These are specifically designed to provide the right intensity and wavelength of light that aquatic plants and fish need without causing harmful temperature fluctuations.

Can Fish See in Darkness?

Fish, much like humans, require a period of rest for restoration. Unlike humans, fish don’t close their eyes as they lack eyelids.

The concept of fish sleep is even stranger and unimaginable for many, as it differs significantly from what we, as humans, perceive as sleep.

During the night, most fish enter a state of deep rest, where their metabolism slows down, and they barely move. Non-bottom dwellers will often just float in a chosen resting spot, resting but still able to move their fins just enough to stay put.

Virtually all fish look for a secure spot to rest, whether it be under a rock, in a cave, among the cover of plants, or in the shadow of a submersible filter.

This applies to both diurnal species, who rest at night, and nocturnal fish, who hide in relative darkness during the day and rummage for food once the lights are out.

Species like loaches and plecos prefer these shady places and caves even when the lights are on. But once darkness descends and the metaphorical party gets started, many nocturnal species venture out.

It’s a good idea to feed such species in the tank when it’s dark, providing them with the comfort they need to thrive. The life underwater is indeed a wicked and different world that, to us humans, remains mostly elusive and fascinating.

Video Tutorial | Aquarium Fish Need Light at Night

How to Observe Fish at Night

If you’re eager to spy on your fish at night, there are a few steps you can follow to ensure you don’t bother their rest and still get a good view of what happens when the lights go off.

Firstly, you will need to turn off the aquarium light and any overhead lamps in the room, allowing the tank to blend into the darkness as it would normally do. Wait for about 15-20 minutes for the fish to adjust to the dark and go about their nocturnal activities.

To observe your fish in the dark, use a small torchlight or the focused beam of a cell phone. In the era of smartphones, there are many decent light options available that provide enough illumination without waking up the fish. Choose in advance the part of the tank you want to observe, ideally a place where fish normally roam around or hide.

Now, cast a light on the chosen part of the tank, making sure the light beams are dispersed and not too intense. Flash the light for about 10-20 seconds before you turn it off. Wait for another 20 seconds and then go again. Repeat this process a few times, always focusing on the same part of the tank.

For the best results, place your torchlight or cell phone at the back of the tank. The scattered light from these sources penetrates the water from top to bottom, providing a special window into the life of your aquatic friends.

However, it’s important not to overdo this in terms of frequency and duration. A few minutes, once a week, should be fine. Anything more could be stressful for the fish. Imagine how you would feel if someone were to cast a light on you every time you tried to sleep!

Keep in mind that checking on your dark tank now and again might wake some fish up. But as long as your light isn’t too bright and you don’t flash it too often, there should still be enough nighttime left for them to get sufficient rest.

Fish don’t go to sleep immediately after it’s dark, but if you wait for a while after you’ve turned off the lights, you’ll be able to observe as each fish finds its place to hide, or scurries around for food. By doing this, you’re sure to catch a glimpse of what your fish get up to when they think no one is watching!

Final Thoughts

In conclusion, while direct sunlight can cause harm to your aquarium and its inhabitants, observing your fish at night with a dim light source can be an exciting and peaceful experience.

It allows you to witness the nocturnal behaviors of your aquatic friends without disturbing their natural resting patterns. Remember to be considerate when using a light source in a dark tank, as too much exposure can cause stress to your fish.

With proper care and attention, you can safely enjoy the beauty of your aquarium at all hours of the day. So go ahead and turn off those lights, and let your fish have their moment in the dark!

FAQs

Is direct sunlight good for a fish tank?

No, direct sunlight can cause harmful temperature fluctuations that can stress or even kill your aquarium inhabitants. It is best to use a dedicated aquarium light for proper lighting.

How can I observe my fish at night without disturbing their rest?

Turn off tank lights, use a dim light like a torch or phone beam to observe fish in the dark. Be considerate of their resting patterns, avoid stressing them. Sit back, relax, and enjoy the show!

Do all fish sleep at night?

No, not all fish are nocturnal and rest during the night. Some species may have different sleeping patterns depending on their natural habitat or behavioral traits. It’s best to research