We all know the importance of sleep for humans – it contributes to a healthy metabolism, regulates our hormones, helps with our cognitive functions, and keeps our cardiovascular system healthy. The same applies to animals – they all require a set number of hours of sleep per night to maintain their health. The sleeping habits of animals are fascinating to observe, especially animals that live in unusual environments, like water. If you’ve ever asked yourself, “Do fish sleep?”, our article will help you understand all about the way fish sleep, when they sleep, and whether the sleep of pet fish differs from that of fish that sleep in their natural environment.
At the end of our article, you will find an FAQ section where we answer some pressing questions regarding the way fish sleep, as well as some pointers that will help you determine if your pet fish is asleep.
How Do We Know If Fish Sleep?
Before delving into how fish sleep, you might be curious to know how scientists have determined whether or not fish sleep.
Scientists know all about sleep cycles and the different sleeping stages by monitoring our brain’s activity during sleep. Well, it turns out that the process of monitoring fish sleep is quite similar – scientists monitor the brain, body activity, and heart rate in fish during sleep and are able to determine the different sleeping stages fish go through during one sleep cycle.
While it’s a bit hard to determine when fish are asleep, there are some tell-tale signs to watch out for. For instance, they hover at the bottom of the water and they lack responsiveness, similarly to humans.
How Do Fish Sleep?
Just like us, most fish are completely at rest when they’re sleeping. There are some instances of types of fish that remain moving while sleeping to maintain a healthy oxygen level in their bodies. Some fish, like the parrot fish, even wrap themselves in a cocoon that resembles a sleeping bag to prevent bigger predators from getting to them.
You might be wondering: how are fish able to sleep and move simultaneously? The secret lies in their brain. The fish that must remain in motion while they sleep have one half of their brain asleep, while the other half remains active, allowing them to move around and get their oxygen supply.
There’s a slight difference in terms of the sleeping stages – since fish don’t have eyelids, they don’t experience the final sleeping stage of REM (rapid eye movement) sleep. They sleep with their eyes open at all times, except some types of sharks that close their eyes while sleeping. Zebrafish are quite fascinating in this regard – not only do they also have different stages of sleep like us humans, but they also seem to have a distinct circadian rhythm.
Do Fish Get Sleep Deprived?
Another question we might ask ourselves is whether or not fish have the ability to get sleep deprived. Getting enough sleep is crucial for the health of every animal on earth, and fish are no exception.
If a fish doesn’t get enough sleep, it experiences many symptoms of sleep deprivation. While this can have negative consequences, the fish make up for it by napping the next day.
Where Do Fish Sleep?
If you’ve ever had a pet fish, you might’ve noticed that it sleeps on the bottom of the aquarium. While some fish do remain at the bottom of the sea/ocean while they sleep, many others have quite unusual sleeping places.
To protect themselves from predators, some fish shelter themselves in coral reefs at night. There are some, like rainbow wrasse, that burrow into sand as soon as dusk falls to protect themselves from any accidents during sleep. As we already discussed, some fish have developed a coping mechanism that allows them to wrap themselves around in a mucus cocoon to shelter from any outside influence. Sharks are known to retreat to caves while sleeping.
When Do Fish Sleep?
It’s natural to assume that all animals have evolved to sleep during the night, just like us humans. However, it turns out that that’s not the case with some types of fish. Some smaller types of fish, such as the three-spot wrasse, have evolved to sleep at night by either hovering near the bottom or wrapping themselves in a cocoon. However, there are also fish that sleep during the day and hunt at night, like some types of sharks.
What About Other Animals?
If you’re interested to know all about fish and their sleeping habits, you might also want to learn about how it differs from other animals.
The first main difference between how other animals sleep and how fish sleep pertains to their brain activity during sleep. Mammals, for instance, experience REM sleep during one of their sleeping stages, while that’s not the case with fish. Mammals that do experience REM sleep exhibit similar changes in their brain and body activity as humans; their breathing and heart rate increase, their brain activity spikes, and there’s a noticeable rapid eye movement, which is where this sleeping stage gets its name from.
Dolphins sleep in quite a similar way to fish. They remain in motion while they sleep, usually moving in circles near the surface of the water. Just like fish, part of their brain is inactive, allowing them to sleep, while the part of their brain that’s active allows them to move around and perceive any danger if necessary. They require this movement not only to protect themselves from any potential danger, but also to get enough oxygen into their body.
How Do Fish Sleep In a Tank?
Fish that are kept as pets have very similar sleeping patterns to fish who live in their natural environments. Their exact sleeping behaviour depends on the type of fish. For instance, some hover near the bottom of the tank and remain mostly motionless, while others move around during sleep to maintain a healthy oxygen level.
Regardless of the type of fish you have, it’s important to provide the ideal sleeping conditions for them to thrive. If you keep different types of fish, don’t forget to take into account how they might like their temperature, light, and what accessories they might need.
How to Tell If My Fish Is Asleep
Now that we established that fish do sleep, we’ll share some ways you can determine whether or not your fish is asleep.
Most fish that are kept as pets don’t move around, so the first sign you should look out for is whether they’re motionless, usually hovering at the bottom of the tank. If you’ve observed that they haven’t moved in minutes, chances are they’re sleeping.
Another easy way to determine if they’re really asleep is to measure their response time. Fish in slumber don’t often react to external stimuli that might be disruptive for fish that aren’t sleeping, such as exposure to light or movement in their aquarium.
If you study your fish carefully, you might notice that it follows certain sleeping patterns. Another way to tell if your fish is asleep is to notice when they usually fall asleep and note down the time.
Some fish like to hide under rocks or any accessories you might keep in the tank. They love to wedge themselves between objects, so if you have a large tank, it might be hard sometimes to find them while they’re sleeping.
How Do You Know If a Fish Is Sleeping?
There are some clear signs which indicate that your fish is sleeping. For instance, they would usually hover at the bottom of the tank motionless and they don’t respond to any stimuli.
Do Fish Sleep During the Day?
Some types of fish, like certain species of sharks, use the night to hunt for food and sleep during the day.
Do Fish Have Naps?
Just like humans, if fish fail to get an adequate amount of sleep during the night, they make up for it by napping the next day.
Like most animals, fish sleep on a regular basis. Scientists have monitored their brain activity and have found out that they also go through different sleeping stages. The main difference is that they don’t have a phase of REM (rapid eye movement) sleep since they don’t have eyelids.
The sleeping patterns of fish depend on the fish in question. Some like to hover at the bottom of the sea/ocean and remain mostly motionless, while others move around a lot to provide the necessary amount of oxygen for their bodies. Additionally, some fish like to hide in caves and reefs while they’re sleeping. The time of day they sleep also differs – smaller fish are usually nocturnal sleepers, while bigger fish like some types of sharks use the night to hunt and sleep during the day.