What Do Fish Do at Night

If you were to ask 100 people this question, more than likely, all 100 would say that they sleep. Because ALL creatures sleep, right? Wrong! There are many creatures who do not sleep at night. They just ‘hide’, reduce their metabolism/energy, and rest.

Because fish do not have eyelids they do not ‘sleep’. Some will float close to the surface and others closer to the bottom. They rest while floating by lowering their metabolism, breathing, and heart-rate. They are re-energizing.

Snakes, night-lizards, and geckos do not have eyelids. They have what is called brille. A clear coating that appears to keep things like dust and dirt out of their eyes. Fish also do not have eyelids. Because fish do not have eyelids they do not ‘sleep’. So, if fish can not sleep at night, what exactly do they do at night?

Fish will hide behind plants or between rocks in the aquarium and rest. Some will float close to the surface and others closer to the bottom. They rest while floating by lowering their metabolism, breathing, and heart-rate.

Besides conserving energy while resting at night, what else do aquarium fish actually do? We are going to explore this in detail. We will explore what Betta and goldfish do, we will answer whether they eat at night, swim, or can if they can see. So, if you are ready to learn about fish then let’s get started.

Why Do Fish Not Have Eyelids

Fish do not need eyelids, really. Eyelids are to help your eyes stay hydrated (each time you blink, it moisturizes your eyes). Fish live in water, which keeps their eyes hydrated, so they have no need for eyelids.

Eyelids also help to keep out dirt, dust, and other debris that may be in the air. Things that find their way into our eyes can cause us to have what is called ‘dry eye’.

Fish also do not need to work about this, because they live underwater. 

There are a few species of fish, like sharks, that have special eyelids. They are transparent and thick. It is speculated by scientists to be similar to glasses, helping the fish to see and focus better. 

What Do Betta Fish Do At Night

Betta fish are not considered nocturnal. Nocturnal fish sleep during the day and hunt at night. Even though betta fish do not have eyelids, it is said that they do ‘sleep’, or rest, as most scientists like to say. So, that must mean that all fish sleep.

It would/could be compared to a human who is daydreaming. Our eyes are wide open, but we are off somewhere else and not focused on our surroundings or what is going on around us. Without eyelids, it looks like fish are sleeping with their eyes open.

Even though they are ‘sleeping’ the betta’s can sense movement in the water. It is stated that they only sleep when the lights are off. So if you want to watch them sleep, you need to turn out the lights and watch them closely. Betta fish will find a comfortable spot on the bottom of the aquarium.

Look very closely and you can see their gills moving slowly. They are in a relaxed state, re-energizing from the days swimming and other activities. 

Sometimes they will hide behind the filter or on top of a plant. They become motionless unless they sense movement or become startled by a loud noise or the lights being turned on. They will also appear paler in color with the lights off, as they rest. Their colors seem to brighten back up, once the light has been turned on.

How Do Goldfish Sleep/Rest

Because goldfish are such a popular aquarium fish, I wanted to make sure that I included some information and insight on them. 

Goldfish will stay in one place, slowly moving to stay stable, and they will become a lot less active. Just like the betta fish, goldfish ‘sleep’ with their eyes wide open because they do not have eyelids.

Goldfish will usually hover an inch or 2 off of the bottom of the aquarium. Goldfish actually change color at night as a safety precaution. Becoming paler in color helps them to hide from any predators that you may have in the tank. But this mostly applies to goldfish that live in a pond. 

Most fish, including the goldfish, sleep when it is dark. You can actually train your fish when to sleep. If you turn off the tank lights at night, they will learn to rest while you do.

If you have the aquarium in a dim room and leave the tank light off, they will hide in or behind plants so it is dark enough to sleep during the day. 

If your fish are not getting enough sleep, they can not replenish their energy or metabolism which can then cause them to become sick from the inactivity. They will also not be able to fight off any infections if they are not getting enough rest.

Can Fish Sleep If You Have A Blue Light in Your Tank

The blue light that some people put in their tanks is meant to represent or mimic the moonlight. The blue light is not going to affect the night and day routine that your fish have. It will also not hurt your live plants or promote the growth of algae.

If you only have a regular light, make sure you turn it off each night. Fish biologically need 8-12 hours of light. But they also need periods of dark as well. It gives them a chance to rest, cool off from the heat of the lights, and re-energize. 

The blue light will also help encourage more physical activity in your fish. It will provide illumination and it makes it easier on our eyes when we want to sit and watch fish.

Do Aquarium Fish Eat At Night

Aquarium fish will normally eat whenever they are hungry, if they can find food down on the rocks. Otherwise, they will eat when you choose to feed them. Even if they are not really hungry, they will gobble up the food.

Depending on what type of fish you have in your tank, will determine how often you need to feed them. Most fish can live on once a day, there are a few that do better or prefer twice a day, and young growing fish should be fed 3-4 times a day. 

No matter how many times you feed your fish, remember, do not give them more than they can eat in 45 seconds to a minute. The rest will just fall to the bottom of the tank and aid in a murky looking tank within a few days (if you are feeding them too much).  Too much food at feedings can also plug up your filter, making the water unhealthy for your fish.

Can Fish See In The Dark

Goldfish, guppies, betta, and other aquarium fish do not see well, or at all, in the dark. Not with their eyes anyway. Fish will sense other fish by the changing movement or pressure changes in the water. 

An aquarium fish doesn’t have the same sleeping patterns as a human. They need the dark to rest, but also can (and do) rest during the day. The darkness allows the fish (and all living things) to simulate the diurnal-cycle.

According to Wikipedia, the diurnal-cycle occurs every 24 hours. This happens because of the full rotation of the earth. It involves temperature variations and growth of plants. It  also includes light and can even affect clinical depression in humans.

What Do Aquarium Fish Do at Night

All fish learn to tell the difference between night and day. They can sense the warmth of the sun, shining down into the water (they have the same sense and feeling from the lights in the aquarium when they are turned on). Most fish are more active during the day, but there are also some fish who like to ‘nap’ throughout the day. Remember, nocturnal fish are asleep during the day. 

You also have other fish; in lakes, ponds, and streams that live in deeper water. Therefore they can not really tell the difference between night and day. Aquariums are not deep enough for this situation to occur. So your fish will learn when it is daytime and when it is nighttime, with your help, when you turn the aquarium lights on and off.

You will notice your fish hovering, in one spot, for long periods of time. Barely moving to keep themselves stable. This is when they are ‘sleeping’. Their gills will move slowly, indicating that they have slowed down their breathing and metabolism. Most fish will sleep at night and are active and playful during the day. As long as you have the aquarium lights off, they will rest. 

Guppies will float near the surface of the aquarium when sleeping. The neon tetras will change their color at night, when the lights are turned off. It is suggested that part of the reason they change colors is for defense. The neon tetras will hover near the bottom, but not touching the rocks or sand. Other fish in your tank may hide behind or wedge themselves between rocks or plants. 

Can Fish See Humans

There were studies that came out in 2016 that stated that fish could distinguish a familiar face. Fish do not have the part of the brain used for facial recognition as humans do. Biologists chose fish for this study because they have tiny, simple brains. They focused their study on Archerfish. This is a species of tropical fish. The Archerfish will spit at insects so that they will fall, allowing for capture.

To get the archerfish to recognize a human, or at least some features, they would show them a picture of someone. The same picture day after day after day. Gradually they added other pictures to see what the response would be.

If they seemed to get a little excited, or a little more active, when shown the on picture then they would receive a treat. If they couldn’t decipher or show excitement, then the scientists concluded that they can recognize some facial features, over time. 

If you think you need to purchase an archerfish, I hope that you have a 100+ gallon tank. If not, you are going to need to get one. These tropical fish grow to be 12-15 inches long. It is recommended to only have 1 or 2 in a tank, so that they have plenty of room to swim around when they are full grown. 


There are a lot of similar things that fish do at night. Most fish slow down their metabolism, and re-energize. Nocturnal fish are the only fish that are active after the lights go out. These fish will sleep during the daylight hours. 

Most fish will eat when hungry, or will learn the schedule of when you provide food for them. Remember that younger growing fish will need to be fed 3-4 times a day. All other fish can survive on one feeding a day. 

There are many different species of fish out there that you can put in your aquarium. They all have their differences in size, color, shape, and behavior. But in the end, they are all extremely similar. They are all beautiful fish that can bring relaxation and joy to the whole family. 

They may not be able to see at night, but if they see you every single day, they will eventually recognize certain facial features. They may begin to get excited when it is feeding time, because they will get used to eating at the same time everyday. Or they may get excited when you get home from work and you walk in to check on them and say, ‘hi’. 

If you take care of fish properly, they can last quite a long time. Giving you something to enjoy with family and friends who visit your home. They are simple, beautiful creatures that can bring so much joy to children. 

I hope we have given you some good insight into fish and what they do at night. What they eat, can they see, do they sleep, and more. It was our intention to give you the best information that we could find, to answer any questions that you may have. 

Until next time everyone! Remember: feed them less, clean the tank once a week, and be sure to research all topics and characteristics before you purchase different species for the same aquarium. Take Care.


I'm passionate about fish pets and love sharing everything I learn about them.

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