Do Fish Need Darkness To Sleep?

Do fish need darkness to sleep? Fish don’t really sleep in the way that we do. They do, however follow their own circadian rhythm – their physiology and behavior changes depending on the time of day. When it is daylight fish become more active, they move around and eat, when it is dark fish slow down and conserve energy, some fish simply stay still, others hide themselves away in a safe spot – this is their version of sleeping

If a fish is subjected to too much light, or indeed too much darkness it disrupts the fish’s circadian rhythm which can cause the fish stress and to become ill. Periods of darkness are therefore essential for fish to remain healthy and happy. (source)

Fish are often motionless while "sleeping"

Do Fish Need Lights Off At Night?

Fish require periods of darkness just like humans do. Although you might think your aquarium looks lovely all lit up and want it to be that way 24/7, your poor little fish would soon become very stressed and more than likely become unwell.

You need to ensure that your aquarium mimics your fish’s natural environment and this includes providing “daytime” and “night time”. For most people, the easiest way to do this is to have your aquarium lights on during the day and then switch them off in the evenings so that your fish “sleep” at the same time as you do.

Can Fish Sleep With Room Light On?

It is far better for your fish if you provide periods of complete darkness. Like humans they can and will still “sleep” with lights on, but doing this too often will confuse their circadian rhythm.

Ideally, you should have your aquarium lights on during the day and then switch them off in the evening and let the room lights light the tank. Just like the sun going down in the evening this prepares the fish for night time. When you go to bed yourself, switch the room lights off to allow your fish to sleep.

In the morning the process is reversed. Before putting the aquarium lights on, give the fish a few hours of natural daylight, or room light – this mimics the sun rising and allows the fish to know that it is now daytime.

How Many Hours Of Darkness Do Fish Need?

When keeping fish, your job is to replicate their natural environment as much as possible. If you do that, your fish will live long and happy lives. Part of this is to ensure you provide your fish with “daytime” and “night time”.

For most places, it is dark for at least 6 hours and often more. It’s therefore advisable to ensure your aquarium is dark for around 8 hours each night. This will ensure that your fish have suitable day/night periods.

Do Fish Need Blue Light At Night?

Your fish don’t need to have blue light on in their tanks at night but it can help to replicate the day/night cycle. A blue light helps mimic the times when the sun would be rising or setting. The blue light is softer than the normal aquarium lights and replicates moonlight coming through the water.

I would still recommend to have a few hours, at least 6 where there are no lights at all but using a blue light can help maintain your fish’s circadian rhythm and what’s more your fish will look stunning under the light too!

What Do Fish Do At Night?

Most fish spend most of their time resting and conserving energy during the night, their metabolisms slow down, their colors fade and for all intents and purposes they sleep!

Some fish however do prefer to be more active when it’s darker particularly at dawn and dusk – it depends on when they would be most likely to find food in the wild.

How Do Fish Sleep In A Tank?

Understandably, fish are much more vulnerable when sleeping so they tend to lay motionless in dark crevices or hide behind rocks where there’s less chance of being seen by predators. Some fish will lie still near the surface of the tank while others tend to lie at the bottom on the substrate.

Some fish however will still remain partially active even while “sleeping”. They may swim around the tank at times but will generally stop before getting too far away from their hiding place.

How To Tell If A Fish Is Sleeping?

You can tell if a fish is sleeping if it is still and relatively motionless normally at either the top or the bottom of the tank. If there are other fish swimming around nearby, the “sleeping” fish will be slow to react, if it reacts at all.

Quite often, the colors of the fish will fade when it’s sleeping and if you pay close attention to their gills you might just be able to tell that their breathing is slower as normal.

Do Betta Fish Need Darkness To Sleep?

Like most fish, betta fish do require periods of darkness in order to sleep properly. As stated before, “sleeping” for a fish will involve them becoming more still and less active.

Betta fish are no exception to this but there is often confusion about betta fish lights out requirements because they do tend to be more active at night than other fish. Part of the reason for this is that they will often swim around at night looking for food and may sometimes even come out from hiding to do so.

It’s important for a betta fish to have at around 8-12 hours of darkness a day, if not more. You should only be looking to have your aquarium light on for about 8-10 hours a day. Remember not to go straight from darkness to light, this can be quite startling to fish, use room light or natural light to gently ease the fish in and out of darkness.

Do Goldfish Need Darkness To Sleep?

Goldfish do sleep better when it is dark, just like humans do! When a goldfish is “sleeping” they tend to move a lot less than normal, often they will remain completely still. You will normally find that when in this state they stay at the bottom of the tank near rocks, plants or decorations.

Goldfish need around 10 hours of darkness each day to ensure their circadian rhythm isn’t upset. I would recommend not having your aquarium lights on for any longer than 12 hours a day. Keeping you aquarium lights on longer than this regularly will start to have a negative effect on your goldfish’s well-being and behavior.

Do Fish Need Darkness To Sleep? - Conclusion

Most fish do need darkness to sleep properly – although they don’t sleep in the same way that humans or mammals do. Many fish will become more still and less active when they are sleeping often remaining completely still at the top or bottom of their tanks.

As a fishkeeper you need to ensure that you are providing your fish the right conditions and this includes giving them the right amount of light and the right amount of darkness each day.