Do Fish Sleep?

Clownfish in Aquarium Fish Tank with Reef

Whenever you watch fish in an aquarium or a pond, do you wonder if these water creatures ever doze off? Land mammals obviously sleep, but what about them? Do fish sleep?

Like other living things, fish do sleep. Their bodies rest so that they can regain energy and continue to survive. However, the way they sleep is a bit different. They don’t lie down or roll in the sand, and they don’t close their eyes either! Yet they still sleep.

We, humans, know that to sleep, we need to lie in bed and close our eyes. Fish do none of these things, which has caused curious minds to speculate whether they sleep at all. If you’re also skeptical, read on to learn more.

Do Fish Sleep Even If They Have No Eyelids?

Scientists have been studying the peculiar sleeping habits of fish for a long time. They, too, have been puzzled at how fish can sleep with their eyes open, or how some keep swimming while sleeping!

To understand fish’s unique sleeping behavior, we must understand what sleep means for humans and animals alike.

Sleep is when the body stops or minimizes movement, responses to stimuli, and metabolic activities such as digestion, breathing, heart rate, and brain activity. Living creatures, including fish, have these periods of rest to recover their strength and boost their immunity against disease

Fish do sleep; they just don’t sleep in the same manner that we do.

How Do Fish Sleep?

It is generally easy to spot sleeping fish. More often than not, they behave similarly with each other whenever they enter into this rested state. Nearly all fish exhibit these common signs, and knowing them can help you tell whether your fish are asleep:

  1. They pause in their favorite spot for several hours.
    Fish that hover or swim in place for long periods under a rock, between corals, or on top of the sand are just sleeping. As long as they are not floating upside-down or swimming sideways, which are symptoms of sickness or death, there is no need to panic. If you cannot find them anywhere in the aquarium, they may simply be hiding and resting to prepare for another new day (or night!).
  2. They don’t react easily to things that happen around them.
    Fish that don’t seem to care about other fish, or even about you watching them, are most probably sleeping. In contrast to land mammals, however, sleeping fish are highly sensitive to danger and will easily swim away at the first sign of it.
  3. They regularly behave in this way, on schedule.
    Do you know that fish have a sleep routine, too? In truth, they are not that different after all. Like other animals, fish usually sleep at the same time and for the same number of hours every day. They also rest in the same position and the same spot every time.

How Do Fish Sleep In a Tank?

Salt Water Aquarium Fish Tank

Fish species have different sleeping behaviors and preferred resting places. All these largely depend on what type of fish they are, whether they’re diurnal or nocturnal, and other factors, particularly water temperature, lighting, depth, and bottom type, whether sand or weeds or rocks.

Since each species has unique traits and preferences, experienced fish breeders advise that all these factors must be considered when keeping different species together in one tank. This is to ensure that all your fish are safe, happy, and healthy in their new habitat.

Whatever species of fish might appeal to you, it is important to provide the necessary conditions for your pets to survive. Besides the right amount and kind of water, the correct tank size, and a water filtering system, your fish will need rocks, corals, algae, or other structures to shelter them. This environment allows them to sleep and rest better, be it during the day or night!

Here are things you might notice about your pet fish as they sleep:

  1. They drift slowly near the surface of the water.
    Some fish appear to drift at the top of the tank and look less active than the other fish. If they swim rapidly at other times of the day, they are healthy and just sleeping.
  2. They wedge themselves in between crevices, corals, or other objects.
    Corals and crevices are “comfort zones” for some fish. They love wedging themselves in between these things, and it sometimes looks like they were stuck for hours! But if your fish can wriggle quickly to get himself out, there is no need to worry.
  3. They hide under rocks or other structures.
    Occasionally, fish mysteriously disappear from the tank for a long time. If this happens, there could be three possibilities. One, your feline pet may have pawed them out. Two, bigger or predatory fish may have eaten them, such as angelfish preying on goldfish. Third, they may just be hanging out under the rocks and have fallen asleep.
  4. They bury themselves in the sand or mud.
    Other fish rest better when their bodies are buried in the mud. At times, they may appear dead, but that’s far from the truth.

Check out this informational video on how fish sleep.

If you’re looking for an excellent fish tank, the Hygger Horizon 8 Gallon LED Glass Aquarium Kit for Starters (view on Amazon) might just be the next perfect home for your water-loving pets! Besides its classy look that will surely enhance any living room, this aquarium includes a built-in filtering system and soft LED lighting that can easily be adjusted.

Sleeping Behavior of Certain Fish Species

Great White Shark in Deep Blue Ocean

By now, you might be asking how certain fish behave while they sleep. Below are interesting facts about some familiar fish:

Sharks continue to swim while they sleep.

This is not a myth! Large fish, like some species of sharks, need to keep swimming even while sleeping so that water flows steadily over their gills, letting them breathe. Other sharks can lie restfully on the seabed because they have spiracles that help them breathe. Experts agree that sharks who can “sleep swim” have brain parts that are resting or unconscious, while other brain parts control their swimming motions.

Parrotfish surround themselves with mucus.

One of the things that set parrotfish apart from other fish is their capability of secreting mucus while they sleep. This mucus secretion creates a cocoon-like layer that protects them from attackers. Quite cool, isn’t it?

Goldfish can change color and also be trained to sleep regularly.

If you have pet goldfish, you might have observed that they never seemed to sleep. Perhaps you woke up during the night to find your orange-colored pet still swimming. Do goldfish sleep?

Fish enthusiasts are torn about whether goldfish are nocturnal or diurnal, but they do agree that goldfish, like most other fish, sleep when it’s dark and quiet – obviously at night, when you and I are asleep. This explains why most of us never catch them snoozing.

Goldfish can be trained to sleep regularly by switching on and off the aquarium lights at the same time each day. Their surroundings must also be quiet when the lights are off.

When goldfish sleep, they hover in place, about an inch from the bottom of the tank. Their bodies are still balanced, not tilting or upside-down, and their heads face down a bit. Some goldfish species slightly change in color to protect themselves from predators.

Betta fish sleep longer than they are awake.

Betta Fish

Siamese fighting fish, popularly known as betta fish, are a beautiful fish species that frequent breeders’ aquariums. The male bettas are particularly famous for their flashy, vibrant colors and long, graceful fins. However, they are highly territorial, so you cannot keep two or more males in one aquarium without them attacking each other. Nevertheless, a male betta can live with a female plus other fish species, while females can live together.

You might be wondering, do these creatures sleep? In this sense, betta fish are much like goldfish. They are very active during the day and sleep at night when everything is dark and still. Unlike goldfish, though, betta fish also take naps during the day, so they are easier to spot when asleep. They can suddenly pause anywhere in the tank, be it near the top, in the sand at the bottom, or between corals.

If you’re thinking, how long do betta fish sleep? To help your pet bettas sleep better, you must at least give them 12 to 16 hours of darkness. That’s a lot longer than our normal 8-hour sleep! But if you want to maintain healthy and beautiful betta fish, you must be up to the challenge to keep them well-rested.

Conclusion – Do Fish Sleep?

Like any other living creature, fish need that period of rest where their metabolism and other bodily activities slow down. This rested state in fish may look very different on the outside from what we commonly refer to as “sleep.” But in reality, the same inner processes in mammals when they sleep also happen in fish’s bodies. So, say goodbye to your doubts; fish do sleep.

Kris Peter

I am a lifelong advocate of sleep, continually learning, and striving to be better than I was yesterday.

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