If your fish is like me, the answer to this question – do fish need darkness to sleep – would really depend on what the fish watched on the TV before bed.
Jokes apart – since fish are not as vocal about their needs like we are, it can sometimes be elusive to answer a question as simple as do fish prefer darkness or bright lights at night.
Luckily for us, for the greater good, for a step forward in strengthening the friendship between men and fish, some animal science buffs have gone out of their way to actually research whether fish need darkness to sleep or not.
Yep, it’s true.
I did the dirty work for you – skimming through a dozen different science journals and research papers to find out what we know so far about a fish’s sleep habits.
So, this blog is not just going to encapsulate the answer to do fish need darkness to sleep but also a lot more interesting findings on the subject.
Do Fish Need Darkness To Sleep?
Like us and most other mammals, fish cannot do without sleep. A 2007 study on zebrafish showed that when kept in constant light conditions, the fish barely slept at all. Reportedly, light can suppress sleep in zebrafish almost entirely even if they had been sleep-deprived previously.
Here’s a quick link to the study for those interested. This report encapsulates the striking similarities and intriguing differences between aquatic and mammalian sleep patterns.
Similar to us, fish have pineal gland in the head – right under the translucent pineal window. The gland secretes a hormone called melatonin. Darkness causes the pineal gland to start producing melatonin, while bright light forces that production to stop.
Melatonin is responsible for regulating the circadian rhythm, the body’s 24-hour internal clock.
Darkness encourages fish to sleep. And a handful of studies have shown that when short on sleep, fish experience physical and behavioral changes like stunted growth and increased aggression.
So, to sum it up, yes, fish need darkness to sleep. While they don’t sleep the same way land mammals do, the need for darkness to fall asleep is an interesting similarity between us and them.
Before we discuss the intricacies of a fish’s sleeping style, it’s important to know that they don’t sleep like we do. For starters, they don’t have eyelids. They can’t close their eyes.
But at night, they do go through periods of lowered activity and metabolism while still staying alert to danger. Some do so while staying afloat at the middle of the tank, some wedge themselves into a cozy spot in the coral or mud, and some even rest in makeshift nests.
While researching for this topic, I came across a few interesting answers by hobbyists like you and me that only corroborate the fact we already know.
Do Fish Need Darkness To Sleep? Real Answers By Real People!
“Yes, fish need darkness to sleep as they have no eyelids to block out the lights.”
“It’s not like they need complete darkness. A little, indirect source of light should be okay.”
“My fish rests happily with the tank lights off but a couple of lamps on in the room.”
“I’ve seen my fish sleeping with the lights on, but they certainly do it more readily with the lights off. Like all animals, fish have cycles of night and day.”
“I use a 7-watt blue sign bulb for moonlight effect in my 65-gallon tank. It’s on for a few hours every evening, then it’s completely dark.”
“If you think about the wild, most of the time, the night is not lit up in any way other than faint moonlight.”
“Of course. A TV light, a hall light, or a little nightstand light can be too much light for them to fully sleep. Everything should go off for them to sleep.”
As you can deduce from the quotes above, the general notion is that fish need darkness to rest at night. Having said that, I came across this one comment that agrees to disagree. Wanna have a read?
Here you go!
“Anyone that has been out at the ocean or remote lakes at night knows that even with just starlight, the world is never completely dark. While some fish sleep at night, others remain active. You can provide dark shelters by heavily planting the tank or adding rock caves.
The fish that requires complete darkness will find itself a cave or a dark weed bed to sleep in. The nocturnal fish will forage into the night.”
One thing is clear – fish need darkness to “sleep”. The intensity and the length of darkness may vary depending on your or the fish’s preferences, but it’s always wise to dim the lights as night creeps in.
Now, let’s find out how much darkness is too much darkness. Sorry, I know, that sounded wordy.
How Many Hours Of Darkness Do Fish Need?
Fish living in aquariums should receive 12-16 hours of darkness everyday to closely mimic what they experience in the wild. If exposed to too much light or too little light, the fish’s circadian rhythm will get messed up.
I know some hobbyists still like to keep the lights on at night for aesthetic purposes, but I’d suggest otherwise. Using light timers or alarms are some of the most straightforward but successful approaches to regulating your fish’s day and night cycle.
Extended exposure to bright lights can make the fish prone to sleep disorders and stress.
While estimating a fish’s required hours of darkness, there are a couple of things to keep in mind. Some of them are:
- The fish’s species
- The number and types of plants
- The tank’s size and layout
So, it’s undisputed that fish need both plenty of light and darkness throughout the day. But if you leave the fish in the dark for too long, the fish will lose its color and turn pale.
This happens because pigments depend on light. The pigments consist of cells which reflect light and produce color. Without light, they will soon fade.
Can Fish See In The Dark?
Fish commonly found in home aquariums cannot see in the dark per se. They don’t have night vision. But their eyes have certain evolved cone cells that help them partially see at night.
However, you should turn off the tank lights for at least 12 hours to give the fish some time to adapt to the darkness.
Additionally, fish have rows of pressure-sensitive organs that run down each side of the body known as the lateral line. It allows them to sense nearby objects from pressure change in water.
What Happens If You Leave A Fish In The Dark For Too Long?
Initially, the fish will assume it’s nighttime and prepare its body and mind for sleep. The fish will then gradually begin to lose color and turn pale. I’ll explain why.
Cells known as chromatophores are present in the bodies of most fish. These cells are responsible for the coloration. All the beautiful, bright colors that you can see on fish are formed because these cells produce colors when in contact with light.
In case these cells are deprived of light for longer durations, they will stop producing colors.
Also, although there’s not much evidence to support the idea, it is believed that a fish’s immunity level drops when exposed to the darkness for too long. This is probably because their stress level increases when kept in the dark for too long.
Before we end this article, here’s a quick look at some of the most frequently asked questions on fish, darkness and sleep. Don’t skip.
Frequently Asked Questions
How Long Do Fish Sleep?
To be honest, there’s no record or documentation whatsoever of how long fish sleep on the internet. I’d assume they sleep for 8=10 hours on average.
Do Goldfish Need Darkness To Sleep?
Yes, like most beings on the planet, goldfish need darkness to sleep. When the night falls. The absence of light sends an important signal to the body that it’s time to rest.
Related: Can Goldfish Live In Saltwater? Are They Adapting?
Do Betta Fish Need Darkness To Sleep?
Yes, betta fish need darkness to sleep as well. If their sleep is disturbed for an extended period, they become irritable and their immunity is suppressed.
Related: Why Did My Betta Fish Die? 9 Possible Reasons!
Can Fish Be In Complete Darkness?
No, fish cannot live in complete darkness. Ample and ambient light is very much important to ensure their survival and longevity. The best way forward is to emulate the natural day and night cycle.
Do Fish Need Light During The Day?
If your fish tank receives ample natural light during the day, there’s no need to provide additional light. This will only fuel algae growth.
Here are quick links to some relevant and interesting articles related to fish and light:
Final Words: Do Fish Need Darkness To Sleep?
Yes, fish need darkness to sleep. As it is with us, the lack of light sends an important signal to the body that it’s time to rest. Consistent and incorrect exposure to light can alter the fish’s internal sleep clock – interfering with both quantity and quality of sleep.