What Do Fish Do At Night? (It’s Might Surprise You!)

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You’re at home getting ready for bed when you turn out your aquarium light. As you cozy up under the covers, a thought crosses your mind: What are my fish doing right now? 

We’ve all wondered what fish do at night. Now, we’re going to tell you!

Short Answer:

At night, most species of fish rest to reserve and build energy for the next day. However, they don’t sleep the same way other animals do. 

In this article, we will go over everything fish do when they rest at night. We’re also going to talk about the differences between fish sleep and other vertebrate sleep. 

By learning more about how fish rest at night, you can learn more about how to best care for your fish. Read on to get a better picture of what your fish do at night when you’re sleeping!

Let’s dive in…

Do Fish Do Anything At Night?

The bottom line is yes, fish absolutely do a few things at night. However, it’s not much for most species. 

Fish typically take this time at night to rest, the same way we do. Typically, fish will:

  • Reduce their activity
  • Lower their metabolism
  • Find a safe place to rest

They do this to preserve and produce energy for the next day, full of hunting, fighting, and mating. What else is a fish to do?

It’s important to note that not all fish do the same things at night. While many fish are diurnal, meaning they are awake during the day and rest at night, other fish are nocturnal, meaning they are asleep during the day and awake at night (That’s Why your fish more active at night).

A good example of this is the walleye. Walleyes are mostly nocturnal and do most of their hunting at night when their prey can’t see as well in the dark. (*)

This is why fishermen seeking a good walleye may go fishing at or after dusk!

Catfish are also nocturnal. Most of their activity is in the evenings while they swim along the murky floor. (*)

For the sake of this article, we’ll cover fish that are diurnal, meaning they’re on the same day/night cycle as us! Most aquarium fish follow this cycle, so you shouldn’t have to worry about nocturnal fish too much.

Important Thing To Remember!

If you do bring home a nocturnal fish, however, be sure it isn’t in a tank with diurnal fish. If you do, each fish species could interrupt the other’s rest. 

Nobody likes a fish that woke up on the wrong side of the tank. 

Reduce Their Activity

When the lights go down at night, diurnal fish will reduce their overall activity. This means they won’t hunt or mate during this time.

Instead, they’ll either slow their swimming or stop swimming entirely. They may gently float towards the bottom of your aquarium and not make many movements.

With the exception of a few fin twitches, fish will not be particularly active. 

Because of this, we recommend you not feed your fish late in the evenings. Though it may be tempting to feed them before bed, feeding them close to their resting time could result in indigestion issues. 

We recommend feeding your fish in the morning at least 30 minutes after the light has been on (to give them time to wake!) or at dusk. This gives them time to eat without it colliding with their rest cycle. 

Automatic fish feeders could be a good option as well for those on a tight schedule. 

Lower Their Metabolism

Since they’re entering rest, fish will lower their metabolism at night. This means they’ll digest and metabolize food more slowly at night.

Fish do this to preserve energy as they rest. If their bodies are busy digesting, they won’t be able to build up as much energy!

This is another reason why it’s important not to feed your fish too close to bedtime. Since they won’t be digesting much overnight, having a full belly may lead to discomfort and stress in your fish. 

We recommend you give your fish time to digest their food for at least 30 minutes before tucking them in for the night.

Rest In Safe Places

Finally, fish need a safe place to get as much rest as possible. Since they may be slightly inhibited while they sleep (even though they’ll still be somewhat alert), fish will try to find a place where they can rest undisturbed for the evening.

Fish, like people, don’t like to be interrupted during the night.

These safe places can take many forms depending on the specific species of fish and their instincts. 

Some fish may burrow into sand or mud to protect themselves and keep themselves from drifting away while they sleep. Others may wedge themselves between rocks as a barrier as well as an anchor.

In your aquarium, your fish may burrow under tank decorations such as caves or chests. They may also hide in aquatic plants to camouflage themselves from predators. 

The moral of the story is that fish don’t like being vulnerable. If they feel too vulnerable or unsafe, they won’t be able to rest as much as they really need to.

To prevent this, always be sure to provide lots of hiding places for your fish. This will help them feel safe and secure while they rest in your tank. (*

Depending on the species you have, coral, driftwood, and aquatic plants are all great choices to help your fish hide.

Plus, they make your tank look way cooler. What’s not to love?

How Do Fish “Sleep”?

As we mentioned earlier, fish don’t sleep the same way other animals do. (*)

Other animals may close their eyes and fall into a deep sleep to rest, entirely unaware of their surroundings. The same as us, as we dream sweetly all night, and in a blink, it’s 8 am again. 

Fish do fall into this in some sense, but they’re much lighter sleepers than other vertebrates. Because there are so many predators for fish, they have to stay at least somewhat alert even while resting. 

So, how do you know if a fish is sleeping? One big difference in how fish “sleep” is that fish don’t have eyelids. While we are able to close our eyes physically, fish’s eyes are always open. 

Note:

Don’t enter a staring contest with a fish, you’ll lose. 

Do fish have eyelids? It really isn’t a big deal that fish don’t have eyelids. Our eyelids are designed to keep our eyes moist and clear of debris. (*)

Since fish are in water all the time, their eyes are always moist. The water also becomes dark at night, so they don’t really need to shut their eyes away from light. 

Fish do, however, still look for safe places to sleep.

Do fish sleep on their side? Like we said before, fish may find safe places to rest that will hide them from predators such as mud or coral. These places tend to be peaceful so the fish isn’t disturbed during rest either.

Once this peaceful place is found, the fish is able to relax its body and fall into a gentle snooze without having to close its eyes. It may float softly near the bottom of the water or wedge itself in a safe spot while it rests. 

This is why it’s so important to keep your aquarium on a regular light cycle! We recommend keeping your aquarium lights on a regulated cycle so your fish get used to when it is going to become “night” when the lights go out. 

This is when your fish will get their beauty sleep, and dream of tasty shrimp and cozy coral. 

This fish sleeping video will explain your fish sleep might look like.

Do All Fish Sleep All The Time? 

Though fish need to sleep regularly, there are certain times when a fish may take a break from resting. 

One example is tilapia. This species of fish doesn’t even start sleeping until they’re around 5 months old!

Yikes. Talk about a cranky baby.

At the same time, fish that are actively caring for their young likely won’t sleep for several weeks if not months. A fish’s instinct is to protect its young at all times, which means little to no rest while guarding against potential predators. 

Sticklebacks are actually more active than ever while caring for their eggs, as the male must use their fins to fan oxygenated water over the eggs without rest until they hatch. 

We don’t know about you, but we’d rather just change a diaper.

Now You Know

Now, you don’t have to wonder what your fish are doing at night. You also now know why it’s so important to turn out the light in your aquarium at night, as without this fish won’t know when to rest!

It’s important for your fish to rest so it preserves its energy and doesn’t get too stressed. After all, imagine how you’d feel if you didn’t get to rest regularly!

We hope you learned something from this. If you enjoyed this article, please comment below on some other topics you’d like to see us cover. We may choose to write on it next!

Up Next: Can Fishes See In The Night?

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