While it’s hard to tell at a glance, angelfish do sleep. Just like all animals, they use this time to rest and recharge. It’s easy for fish owners to assume that their fish doesn’t sleep at all. You may even mistake a sleeping angelfish for being sick, injured, or dead as it rests.
Angelfish sleep by reducing their mobility and becoming very still. They do not become completely unconscious, but will limit the amount of energy that they burn. At nighttime, angelfish will stick to the bottom of the aquarium, and their physical stripes will fade slightly. This lets them recoup energy and heal. If angelfish sense activity or feel threatened, they will immediately become alert.
Because angelfish are such light sleepers, they do not experience REM cycles. They do not dream or lose awareness of their surroundings. That’s because angelfish are prey animals and need to stay constantly alert. If they went into a deep sleep, they wouldn’t be able to detect and escape predators. If your angelfish stops moving, but doesn’t float belly-up, don’t worry as it’s just resting.
Do Angelfish Sleep?
Angelfish do sleep, just not the same way as mammals or humans. Instead of going into a deep, unconscious sleep, angelfish reduce their activity and stop reacting to most stimuli.
During this time, angelfish will gently float along with the currents of the water. Small gestures with their fins may be used to correct their course. However, the fish will not:
- Swim actively
- Interact with other fish
- Respond to light or movement, unless it makes them feel threatened
The stripes on the body of the angelfish offer the most compelling proof of its sleeping ability. Because the fish’s metabolism slows, it’s unable to maintain its bright coloring. The stripes fade slightly during this time, but will brighten up later when it awakens.
Do Fish Sleep Like Humans?
When humans sleep, we progress through multiple stages of unconsciousness. One of these stages includes deep sleep, or the REM cycle. Fish don’t experience this whatsoever. They do not fall unconscious when they rest, nor do they dream.
Some fish even bury themselves in the sand while they rest. This helps them to better absorb melatonin and maintain a strong sleep cycle. While angelfish don’t bury themselves in your tank’s sand or gravel, they will reduce their activity to near zero.
An angelfish remains partly awake as it sleeps. In other words, it’s a light sleeper. It will use this time just like every other creature. Its body will begin to heal its cells, improve brain function, and recoup energy.
As a plus, this light sleeping doesn’t have any of the negative aspects that mammals find with deep sleep. Angelfish don’t:
- Become unaware of their environment
- Struggle to return to their full energy and alertness when awoken
- Fail to perceive threats or the arrival of predators
That’s important because angelfish can be aggressive creatures. As members of the cichlid family, they’re often expected to defend their territory and mates. They may even be attacked by other angelfish that want to establish dominance. This light sleeping ensures the fish can snap to attention exactly when it needs to.
How To Tell An Angelfish Is Sleeping
It’s easy to look at a motionless fish and wonder if it’s dead. You may even rush to help the fish, only to see it jerk back to life. Luckily, there are several indicators that you can look for to identify a healthy, sleeping angelfish.
Angelfish Not Moving, But Not Belly-Up
If a fish is dead, it will turn belly-up. It may immediately float to the top of the tank, or rise up to that point slowly. This is a bad sign. However, a sleeping angelfish will not be inverted. It will remain right-side-up and stay almost completely still.
A dead angelfish will have fogged eyes and a grey appearance. If it’s passed recently, this change will be gradual.
However, a sleeping angelfish will not have any changes to its eyes. Its stripes will fade slightly and its color will dim. However, it will not appear ashy or grey.
Angelfish Resting On Bottom Of Tank
The bottom of your tank will see the least activity, and angelfish know this. That’s why they choose to swim to the base of the tank, near the gravel, and stay there. Other fish can swim and interact above it without disturbing it.
Will Not Attract Other Fish
As the angelfish sleeps, most other fish will ignore it. This is a good sign, as the rest of the life in the aquarium goes about its business. If the fish is dead, other tank occupants might investigate the body as a source of food.
Do Angelfish Sleep Upside Down?
Angelfish do not sleep upside down. If your fish has turned belly-up, this is a sign that it is extremely ill or has already died.
When an angelfish is sleeping, its swim bladder will remain in perfect condition. This helps the fish to maintain its balance and equilibrium as it’s suspended in water. This only changes when the fish dies or has its swim bladder damaged by an infection.
Do Angelfish Sleep On Their Sides?
In that same vein, angelfish don’t sleep on their sides. This is a quick way to tell if your fish is ill or has damage to its swim bladder. If it starts floating on its side or swimming sideways, then it needs veterinary attention.
Do Angelfish Move When Sleeping?
Even a resting fish may create very small movements. This is designed to correct its course as it floats along, and keep water flowing over its gills. Since angelfish need to absorb oxygen from the water, this keeps the water flow consistent. In a well-aerated tank, the fish will need to move less often Since it’s not entirely unconscious, the angelfish may:
- Twitch its fins slightly
- Flick its tail once or twice
Likewise, you may notice your angelfish suddenly moving in one direction when you turn on the lights. This happens because your fish is startled out of its sleep. Just give your fish some time to assimilate to the sudden change, and it will start acting normally again.
How Long Do Angelfish Sleep?
So far, there’s no concrete scientific study that answers this question. When an angelfish sleeps, its inactivity and immobility are not consistent. That makes it hard to tell. However, there are things we know about a fish’s sleep cycle, including:
- Your angelfish may ‘wake up’ several times to check for activity or respond to false alarms
- Your angelfish may sleep in short bursts, waking up to check its territory or fry before going back to sleep
- The angelfish may seem to be awake the entire time, since it moves its fins slightly to correct its floating course. In actuality, it’s just sleeping.
The length of an angelfish’s resting period could be as short as a few minutes or as long as a few hours.
Angelfish Sleeping Habits
Every angelfish is different, and will create its own sleep cycle. However, there are a few habits that are consistent for all fish.
Angelfish Usually Sleep At Night
Your fish will prefer to rest once their tank is dark. In the wild, this indicates nighttime has arrived. For species of fish that live in or around coral, or in shallow waters, they will struggle to see in complete darkness.
This makes it far easier to hide and sleep during this time, when predators may be more active. Since angelfish fall into this criterion, they’re likely to settle down for the night.
Angelfish Sleep With Their Eyes Open
Like some mammals, including horses or dolphins, angelfish do not close their eyes as they sleep. Instead, the eyes remain open to take in movement and light. This allows the angelfish to detect danger and react more quickly if it needs to, even when it’s resting.
Angelfish Slow Down Their Metabolism
To save energy and help recoup their body’s strength, angelfish slow their metabolism as they sleep. It’s the same as a human’s heart rate evening out and slowing down as we sleep.
Your angelfish will digest, breathe, and move blood throughout its body at a slower rate. This metabolism change helps the fish to take a break and regenerate as it needs to.
Angelfish Do Not Dream
According to a study in Physiology & Behavior, fish do show any kind of rapid eye movement as they sleep. This strongly suggests that fish do not dream. Even when they’re at their most restful, they do not enter a REM cycle or deeper stages of sleep.
What Do Angelfish Need To Sleep?
Like all animals, your angelfish will sleep when it’s tired enough. However, this may be difficult if its tank conditions aren’t set to the fish’s comfortable range. That will stress the fish out and make it feel too unsafe to sleep. To help your fish rest properly, you should:
- Keep a water temperature between 78° to 80° F
- Give the fish tank that’s between 20-55 gallons
- Avoid adding too many fish to the tank. Otherwise, the fish may feel overcrowded and threatened
- Keep the fish well-fed. Otherwise, they may try to scavenge at all hours
- Separate aggressive fish. They might antagonize each other, especially when one is trying to sleep
Angelfish may not sleep like humans, but they still need sufficient rest. Be sure to give them a healthy environment, so they can visit the bottom of the tank, go still, and take a nap.