Sleep always plays an important role in the overall development, functioning, and how beings live. Without sleep, our cognitive performance and health suffer. The same goes for animals, who need enough sleep to live the way they used to, including fish. 

So, do fish sleep? While nearly all animals in this world sleep, most fish have their way of resting by metabolism and activity reduction. The way fish' sleep' can be different from those of land mammals. If you're curious about how to do fish sleep, then you've come to the right place. In this blog, you will understand more about how they sleep, even if it's confusing sometimes. 

Do Fish Sleep? Know What Researchers Have Said About it

Ever wonder how do fish sleep? There are lots of fish that sleep, but the way they do it is way different from what we think of sleeping. Researchers and Scientists have not been able to measure the wave patterns of their brains that will characterize a human's sleep and animals like fish. 

Therefore, they often refer to the way fish sleep as resting. The nature of 'sleep' in fish has always been active research. Researchers have also found that fish can reduce their metabolism and activity while staying alert to danger. And since they don’t have eyelids, fish can't close their eyes while they rest, making them become more alert than human-beings when asleep. 

Fish can give enough time to react to any potential threats around them. Of course, fish slow down the metabolic processes while resting, just like human beings. They can also slow down physically with some other fish that float in place. 

Furthermore, with some fish floating, others wedge themselves into a more secure spot in the coral or mud. Some fish even look for a suitable nest, which you call "suspended animation", and it may perform the same functions as sleeping does to people. 

Interesting Facts and FAQs About How Do Fish Sleep

If you want to know and understand a little bit more about if you do fish sleep, then read on below for interesting facts. 

1. How to know if the fish is sleeping?

It's very easy to tell when a fish goes sleeping. Several signs will tell that they are sleeping: 

• They lie motionless, usually at the bottom or near the water surface. 
• They are very slow to respond to what's happening around them. There's a chance they don't respond at all. And if you happen to watch their gills, you will notice that they're breathing so slowly. 
• They float in place or perhaps retreat to the bottom or top of the tank or beneath the coral.
• They rest around about the same time every day

If you have fish tanks at home, you'll know that the fish inside the tank becomes less active whenever the lights go out at night. However, if you turn the light in the middle of the night, you will see how still the fish are.

The thing is that people and fish do have internal or body clocks that will tell them to do things like eating and sleep. So whenever you accidentally leave the lights on at night, the fish can settle down and go to 'sleep' or rest anyway. 

Furthermore, lacking responsiveness is usually an indication of fish sleep. However, researchers found additional marks of fish sleeping were shared with humans and other animals. 

2. What are the stages of sleep to fish?

Did you know that when fish don't get enough sleep, they seem very vulnerable, resulting in sleep deprivation? Like the zebrafish, after a night of total sleep deprivation, they end up having a sleep rebound, wherein they catch up on sleep. 

The sleep cycle of humans follows 4 stages of sleep. This includes light sleep, deep sleep, 1 stage of slow-wave, and a stage of a rapid eye movement sleep. And though fish don't have a neocortex just like human beings, researchers could know their heart rate, brain activity, even their eye and muscle movement. This is to document the stages of sleep. 

It is very important to fish to have that resting state. They will always find a way just to maintain even a minimum of sleep, like any other animals. Say, for instance, if the fish is subject to experiments wherein their sleep is being interrupted, they are going to end up getting into micro-sleeps. This will manage to obtain at least five to ten percent of their normal sleep. 

3. Do fish suffer from sleep disorders?

Scientists haven't done much research yet to fish sleep, but there are studies and discoveries that when fish were deprived of sleep using a mild electrical current, they ended up sleeping more when they returned to a normal day or night cycle, of course, not being disturbed. 

However, when fish were kept under constant light for days, they could normally sleep, especially when returned to a regular day or night cycle. Researchers think that the light may inhibit the sleep hormone in fish, yet more research should be needed on this matter. 

4. Do fish swim while they sleep? 

To survive, a fish also needs oxygen. They get oxygen as water passes through their gills. Moving a fin and staying afloat to make water pass around them from time to time. Some fish may get oxygen while in a stationary position and when they face a current.  

Other fish like rays and sharks need to make large movements, so they can move an enough amount of water over their gills. And because of unihemispheric sleep, the larger fish may keep on swimming while they are asleep. The unihemispheric sleep will allow them to put half of the brain to sleep. 

The other half remains active, and allow them to keep swimming slower than being awake. Only if they had their eyelids the eyes that is connected to the sleeping side of their brain could close and the other would remain open, as it does with whales and birds. 

Wrapping Up

Sleep means a lot of things to different forms of life. Much as we need enough sleep every day as humans, we must understand that animals like fish also have their needs in terms of resting. Most of them have a daily pattern of activity and rest, and these daily cycles are somewhat similar to human beings. This is mainly because animals also attain nourishment, do tasks during the day and rest in the evening. 

Being asleep means different things to different fish. It's very easy to see mammals, people, and even birds sleep since they close their eyes and remain motionless. So, whenever we see signs that a fish is resting or sleeping, we must respect it and try not to disturb them. Just put yourself into their shoe, and see if being sleep-deprived will do good for you. The thing is, we need to have empathy, not only for other people but also for animals like fish.

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