Do Pet Fish Really Sleep?

A common question that fish owners often wonder is if their water pets ever sleep. If fish do indeed sleep, then it can be quite hard to tell if they really are or not.

Do pet fish really sleep? Yes, fish do sleep. They sleep with their eyes open because they don’t have eyelids. They can sleep at any time of the day. If it looks like your fish is staying in one spot for a long time, then it’s probably sleeping.

There are quite a lot of facts for fish that do and don’t sleep. Yes, there even are fish that don’t have to sleep at all. Today, we’ll be exploring fish’s sleeping habits, as well as taking a deeper look into how/if they dream.

Sleeping Fish

Fish have to sleep just like humans do. They exert energy throughout the day, just like we do. So, they will have to sleep to regain their energy. They use the food they eat to keep their energy through the day, but they need to sleep to regenerate their body too. They are continuously moving their whole bodies all day. They don’t have a couch they can rest on after a long day.

Fish sleep in different ways than we do. For starters, they sleep with their eyes open. They don’t need to close their eyes to sleep because they can’t. Fish don’t have eyelids to close! The round part covering their eyes that looks like eyelids aren’t eyelids. Those are their eye sockets. For us, our eye sockets are in our skull. For fish, they are exposed but allow them to see a wider view.

One fun fact is that some fish do have eyelids, but those are mainly sharks.

Fish will also sleep at the bottom of their tank. The weight of their bodies floats down to the bottom because the bottom of the tank, most of the time, is where less of the water current is. If anything in the fish tank is making the water move, such as equipment or other fish, it will cause small currents in the water, making the bottom of the tank calmer, which is why fish sleep there.

Sleeping Habits

Sometimes it’s hard to tell if fish are asleep or not. Not only do they always look like their awake, but they still move around when they sleep too. It isn’t the same thing as sleepwalking as people do, but it is sort of similar.

Fish have to keep moving when they are asleep so they can keep breathing. They have to keep a steady current of water over their gills so they can keep breathing. Even though they are surrounded by water, they must keep moving it around.

As fish and even some sharks move slowly through the water so they can keep water on their gills to breathe. Medium-sized fish must keep moving to get enough water over their gills to breathe. Small fish don’t need as much water to breathe, so most of the time all they have to do is move their fins back and forth, and that is enough.

If they don’t keep moving around the water, they would choke. Like humans, fish inhale oxygen from the water and expel carbon dioxide. If they didn’t move around, they would be continuously breathing in carbon dioxide, which would be dangerous for them. That would be the equivalent of being trapped in a box and running out of air.

Sleeping Strategy

Yes, fish need to be smart about how, where, and when they sleep to protect themselves from predators. Some have to find some shelter to protect themselves when they sleep. Others have special defense mechanisms that they developed over thousands of years through evolution.

When smaller fish sleep, they usually find reefs to sleep in, so they are protected from larger predators. Reefs protect themselves from predators by having sharp thorns or shock antenna for predators when they are attacked. Little fish have no problem with these because they are small and can squeeze in between the coral and be safe from invaders.

The Parrotfish has a different method from protecting itself from invaders. When the Parrotfish sleeps, it secretes a jelly-like substance from its body. The substance is mostly made of up mucus, and it encloses itself with some water, forming a sleeping bag to protect not sure quite how mucus is going to protect it, but somehow it keeps the predators away from it.

Other fish have a cloaking technique to use when they hunt and when they sleep. Fish like the octopus us their camouflage when they are hunting for food. They also use the technique when they sleep so they can be safe from predators like sharks, seals, and whales.

How Long do Fish Sleep?

Fish would normally sleep when they want to. However, in fishbowls and tanks, this isn’t the case. In the ocean, a fish would have the ability to swim around as long and as far as they wanted to. In doing that, they could sleep whenever they wanted too.

In a fish tank, this is different. Fish sleep according to how much light source they have. If the tank is dark, they will go to sleep. You would notice that they would stop moving. If there is even a small light on their tank, you’ll notice that they will begin to move around more. Water is the most reflective of all things. So even a small light could wake all the fish in the tank.

If you have a light on, the fish will be awake. Fish in the ocean have periods of darkness and light in their day. For a regular gauge on when a fish should be awake or not, see if it is dark outside. If it is, then you should probably turn out the lights, or find something large enough to cover the tank from light. Fish need sleep just like we do to stay healthy. Don’t ruin that for them.

Do Fish Sleep Upside Down?

No, all fish sleep upright. The only reason wouldn’t sleep upright is if its swim bladder had a disease. The swim bladder is what helps to keep fish’s buoyancy and stay upright. A disease in the swim bladder could mean that the fish is dying. Another thing that this will do is cause the fish to swim abnormally.

If a fish does have a disease int their swim bladder, you would be able to tell by the way they sleep and swim. Fish like this will either sleep, not upright, or will swim as if they are leaning. Swimming and sleeping sideways aren’t necessarily harmful to the fish, but the disease they may have would be. Keep an eye for this if you have pet fish of your own.

The only reason why a fish would be ever upside down is if it died.

Do Fish Dream?

Like us, fish do go unconscious at the time when they sleep. However, they don’t fully go to sleep when they hide from predators at night. They always keep at least one part of their brains awake, so in case they are attacked, they have the time to respond, even as delayed as it is.

The way we can imagine their sleep is the equivalent of daydreaming. Clearly, you aren’t focused on whatever you are supposed to be doing, but if someone tries to talk to you, you can hear them. This is basically what happens to fish. Unfortunately, there is no definitive proof that fish have dreams or not.

In summary, fish do sleep. It only depends on the circumstances of where they sleep that affects them.