Do Molly Fish Sleep? {How Can You Tell?}

Do you stare at our Molly Fish and wonder do molly fish sleep?

How do we know for sure that they are asleep or just floating?

In this article, we’ll find out everything we can about how, when and where Molly Fish sleep.

Do Molly Fish Sleep?

Yes! Your Molly Fish follows a diurnal cycle that requires the lights to be off for 12 hours a night where sleep cycles take place.

Motionless, unaware and upright floating with minimal fin and mouth movements near the bottom of your tank indicates that your Molly Fish is asleep.

How Do Molly Fish Sleep?

It’s completely normal to wonder how your molly fish is actually sleeping. Let’s find out.

First of all, we know that your molly fish do not have any eyelids. If your molly fish is not closing their eyes then how are you sure that they are asleep?

Look for the following signs:

  • Occasional fin movement
  • Minimal motions to enable oxygen to flow into their gills
  • Located near the bottom of the tank

Your molly fish move their fins slightly to maintain an upright balance. The water continues to flow and your molly fish move slightly forward or backwards which enables oxygen flow right into the gills.

Your molly fish actively enjoy swimming throughout all parts of the tank, but it’s normal to swim to a deeper part for some rest and relaxation.

Why Do Molly Fish Sleep?

Molly fish need rest just like humans and many other animals in nature. Just because they do not have eyelids, it doesn’t mean that your molly fish are not sleeping.

Sleep helps your molly fish for the following reasons:

  • Repair
  • Strengthen organs and tissues
  • Process information better when awake

There are many reasons why your molly fish need to sleep, even though they do not carry the same physical behavioral tendencies or dream-like states that humans undergo.

Much of the research continues to be debated and further information is needed to understand what goes on while a molly fish is asleep.

What Does a Sleeping Molly Fish Look Like?

A sleeping molly fish looks like it is not moving or slightly flowing with the water in your tank. Fins of a molly fish move steadily and slowly.

You will not see much movement happening in the mouth or gills. This is when you know that your molly fish has entered a sleeping cycle.

You will mostly notice this happening near the bottom of the tank in a safe and quiet space. If you have planted areas or decorations near the bottom of the tank, it would be a great spot for your molly fish to rest for the night.

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How Long Does a Molly Fish Sleep?

There is no definite proof that a molly fish is sleeping for a certain amount of time. This sleep cycle occurs during the 12 hours where the lights are off in your aquarium.

Your molly fish at this time will go through many cycles of entering in and out of sleep. There are also moments during the day where a molly fish will decide to have a quick nap.

This may only last a few minutes or so. Most of the time your molly fish is active during the day. If you keep the lights on at night, you will disturb the diurnal cycle of your molly fish.

Remember when it’s lights out for you, it’s also lights off for your mollies.

Can Molly Fish Have Trouble Sleeping?

Yes. There are often occasions where your molly fish may have difficulties getting the amount of rest they require to maintain healthy functioning and thriving lives.

The following examples indicate that molly fish are not getting the amount of sleep they need:

  • females who give birth
  • moments of spawning
  • migration in the wild
  • acclimating to a new environment
  • aquarium lights remaining on during the night
  • stress from tankmates
  • overcrowded tanks
  • tank being too small
  • poor water chemistry

It is up to us as aquarists to manage our tank’s ecosystem in order to create a comfortable environment for our molly fish and their tankmates.

Your molly fish may have trouble sleeping at night if the water quality is off. This is the time when many fish swim erratically and feel extra stress.

Do Molly Fish Sleep Upside Down?

No. If you are noticing that your molly fish is sleeping upside down or to its side, there might be an issue with buoyancy relating to swim bladder disease.

It could also be a case of constipation or bloating that is pushing against the swim bladder and causing your molly fish to lean on its side or upside down.

Any molly fish that is upside down is concerning. Your molly fish might be having trouble balancing its weight or could be very sick to the point where it might be fatal.

What Is The Sleeping Behavior Of Molly Fish?

Sometimes it’s hard to tell the difference between a fish that is sleeping or one that is simply disinterested, lethargic or even ill.

You are looking for the following signs to know that your molly fish is healthy and sleeping peacefully:

  • remains upright
  • hovering above the substrate
  • moving its fins slowly
  • little or no movement of the mouth
  • revived or active once the lights turn on
  • alert when food is present in front of its mouth

A sick molly fish may have trouble breathing, rapid gill movement and lack of appetite. If you notice the signs in the points above, then you should have no worries about your resting molly fish.


Your molly fish definitely sleeps. Even though the sleeping you are seeing looks far different from the way most animals and humans rest, you can rest assured that your molly fish is entering sleep cycles throughout the night.

Keep the aquarium lights off for at least 12 hours each night for your molly fish to get the beauty sleep they deserve.

Brian Arial

Brian Arial has kept fish for leisure and worked with fish stores for most of his life. He enjoys writing and caring for aquariums and ponds.