Miya Pearson
Fish need to sleep, but they don't sleep in the same way that we do. Fish don't have eyelids, so they can't close their eyes, and they don't have a neocortex, which is the part of the brain that shuts down when mammals sleep. However, researchers have found that most fish species enter a restful state where they remain still and experience reduced breathing and metabolic rates, as well as lower brain activity. Some fish can receive oxygen while remaining almost stationary, while others, like sharks and rays, need to make larger movements to move water over their gills. Due to unihemispheric sleep, these larger fish can keep swimming while they sleep, as one half of their brain is asleep while the other half stays active.
| Characteristics | Values |
|---|---|
| Do fish need to sleep? | Yes, like all animals, fish need to sleep to stay healthy and live long, happy lives. |
| How do they sleep? | Fish sleep in a different way to other animals. They remain still, their breathing slows down, and some can be picked up in your hand. Some fish can receive oxygen while in a nearly stationary position by facing a current, staying afloat and moving a fin every now and then as water passes around them. Other fish, like some sharks and rays, need to make larger movements to move a sufficient amount of water over their gills. Due to unihemispheric sleep, these larger fish can keep swimming while they sleep. |
| How is it similar to other animals? | Researchers at Stanford University discovered that Zebra Danios sleep much the same way we do. Using state-of-the-art technology, they monitored brain and body activity in the fish, and were able to identify slow-wave sleep and paradoxical sleep (deep sleep), just like mammals, birds and reptiles. |
| How is it different to other animals? | Fish do not close their eyes because they don't have eyelids. They also do not exhibit Rapid Eye Movement (REM) like humans and other animals. |
| How do they regulate their sleep-wake cycles? | Light-dark cycles are a common regulator of circadian rhythms in many animals. But there are fish that cannot see light, such as deep sea cavefish. Cavefish live so deep in the sea that they live in darkness, and many have evolved without sight as a result. Even so, they display behaviours that are consistent with having a circadian rhythm, leading researchers to believe other environmental factors, like food, may help regulate their sleep-wake cycles. |
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What You'll Learn
- Fish don't have eyelids, so they can't close their eyes
- Fish don't have a neocortex, which is the part of the brain that shuts down when mammals sleep
- Some fish can receive oxygen while remaining nearly stationary
- Some fish, like sharks and rays, need to make larger movements to move water over their gills
- Fish sleep needs may have evolved according to factors in each population's environment
Fish don't have eyelids, so they can't close their eyes
Fish do need to sleep, but they don't sleep in the same way as other animals. Fish don't have eyelids, so they can't close their eyes. Instead, they have a transparent, protective layer called the nictitating membrane. This thin membrane covers their eyes and helps to safeguard them against debris, predators, and excessive light exposure. Some fish, like sharks and rays, have true eyelids that resemble those found in mammals. These eyelids protect the eyes from physical damage, excessive light, and foreign objects.
Fish sleep in a variety of ways. Some fish can receive oxygen while remaining nearly stationary by facing a current, staying afloat, and moving a fin every now and then as water passes around them. Other fish, like some sharks and rays, need to make larger movements to move a sufficient amount of water over their gills. Due to unihemispheric sleep, these larger fish can keep swimming while they sleep. Unihemispheric sleep allows a fish to put one half of its brain to sleep at a time. The other half stays active, allowing the fish to keep swimming, albeit more slowly than when it is awake.
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Fish don't have a neocortex, which is the part of the brain that shuts down when mammals sleep
Fish do need to sleep, but their sleep is different from that of other animals. Fish don't have eyelids, so they don't close their eyes when they sleep. Some fish can receive oxygen while remaining almost stationary, by facing a current, staying afloat and moving a fin occasionally as water passes around them. Other fish, like sharks and rays, need to make larger movements to move a sufficient amount of water over their gills. Due to unihemispheric sleep, these larger fish can keep swimming while they sleep. Unihemispheric sleep allows a fish to put one half of their brain to sleep at a time. The other half stays active, allowing the fish to keep swimming, albeit more slowly than when they are awake.
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Some fish can receive oxygen while remaining nearly stationary
Fish need to sleep on a regular basis to stay healthy and live long, happy lives. However, they don't sleep in the conventional way that we do. Most fish species go into a restful state where they remain still and experience reduced breathing and metabolic rates, as well as lower brain activity.
Fish don't have eyelids, so they can't close their eyes to sleep. They also don't have a neocortex, which is the part of the brain that shuts down when mammals sleep. Despite this, researchers have found that fish do display behaviours that are consistent with having a circadian rhythm. For example, deep sea cavefish live in perpetual darkness and many have evolved without sight, yet they still show signs of having a sleep-wake cycle. This leads researchers to believe that other environmental factors, like food, may help regulate their sleep-wake cycles.
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Some fish, like sharks and rays, need to make larger movements to move water over their gills
Fish, like all animals, need to sleep on a regular basis to stay healthy and live long, happy lives. However, fish don't sleep in the conventional way that we do. Most species go into a restful state where they remain still and experience reduced breathing and metabolic rates, as well as lower brain activity. This is known as unihemispheric sleep, where one half of the brain is asleep while the other half stays active, allowing the fish to keep swimming, albeit more slowly than when they are awake.
Some fish can receive oxygen while remaining nearly stationary by facing a current, staying afloat, and moving a fin every now and then as water passes around them. However, other fish, like some sharks and rays, need to make larger movements to move a sufficient amount of water over their gills. Due to their size, these larger fish cannot remain stationary while sleeping and must keep swimming.
The sleep habits of different fish species vary greatly, just like those of other animal species. Researchers have found that fish's sleep needs may have evolved according to factors in each population's environment. For example, deep-sea cavefish live in perpetual darkness and have evolved without sight. Despite this, they display behaviours consistent with having a circadian rhythm, suggesting that other environmental factors, such as food, may play a role in regulating their sleep-wake cycles.
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Fish sleep needs may have evolved according to factors in each population's environment
Fish do not have eyelids, so they cannot close their eyes. They also do not have a neocortex, which is the part of the brain that shuts down when mammals sleep. Despite this, scientists have observed behaviours in fish that are consistent with having a circadian rhythm, suggesting that other environmental factors, such as food, may help regulate their sleep-wake cycles.
Some fish can receive oxygen while remaining nearly stationary by facing a current and moving a fin occasionally as water passes around them. Other fish, like some sharks and rays, need to make larger movements to move enough water over their gills. Due to unihemispheric sleep, these larger fish can keep swimming while they sleep, allowing them to put one half of their brain to sleep at a time while the other half stays active.
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Frequently asked questions
Yes, like all animals, fish need to sleep to stay healthy and live long, happy lives.
Fish sleep in a different way to other animals. When they sleep, they remain still, their breathing slows down, and some can even be picked up in your hand. However, they don't close their eyes because they don't have eyelids. Some fish can receive oxygen while in a nearly stationary position by facing a current, staying afloat and moving a fin every now and then as water passes around them. Other fish, like some sharks and rays, need to make larger movements to swim water over their gills. Due to unihemispheric sleep, these larger fish can keep swimming while they sleep. Unihemispheric sleep allows a fish to put one half of their brain to sleep at a time, while the other half stays active.
No, the sleep habits across and within different fish species are as varied as those of other animal species. For example, deep-sea cavefish live in darkness and many have evolved without sight. However, they display behaviours that are consistent with having a circadian rhythm, leading researchers to believe other environmental factors, like food, may help regulate their sleep-wake cycles.
Researchers at Stanford University discovered that Zebra Danios sleep much the same way we do. Using state-of-the-art technology, they monitored brain and body activity in the fish, and were able to identify slow-wave sleep and paradoxical sleep (deep sleep), just like mammals, birds and reptiles. The only difference was that during paradoxical sleep, they did not exhibit Rapid Eye Movement (REM) like humans and other animals.
