Do Koi Fish Sleep?

From its humble beginnings in the rural farmlands of Japan over a hundred years ago, the hobby of koi raising has exploded in popularity all over the world recently. Many people love collecting ponds full of majestic koi, thanks to their natural beauty.

Despite this, there are still many things about koi fish that remain a mystery to us. For example, do koi fish sleep? You would think this would be an easy question to answer, but it isn’t quite so simple.

How Koi Fish Rest

If you were to observe koi fish at night, you wouldn’t be able to tell whether they were awake, or asleep. This is because they just sit there in the water, motionless and unblinking. You may even be surprised to learn that koi fish can’t blink at all. Similar to most other fish species, koi don’t have eyelids.

However, most experts seem to agree that although koi don’t ‘sleep’ in the traditional sense of the word, they do enter a relaxed state at night, during which they are far less active, and you can barely even tell they’re breathing. This form of sleep isn’t the same as how humans and other animals sleep, but it’s also not entirely dissimilar.

Humans often toss and turn in their sleep. Some prefer to sleep on their backs, others prefer to sleep on their stomachs, and there are those that sleep on their side. Koi fish are quite different, in that they don’t move around nearly as much in their sleep, or at all for that matter.

If you happen to see a koi lying on its side, they aren’t sleeping. They could be deprived of oxygen, dying, or already dead, and you should check them immediately.

Where Koi Fish Rest

To avoid predators that may come out at night, koi rest either at the bottom of their pond or closer to the middle. Another interesting fact to note is that most of the time, koi fish will sleep close together. This is a sign that your pet koi have grown attached and feel comfortable around one another. By sleeping together in a cluster, koi fish can protect one another from predators.

What Is Sleepy Disease?

Carp Edema Virus is a sickness commonly found in koi and other species of carp. It is colloquially known as koi sleepy disease. As a koi fish owner, it’s important to keep a close watchful eye on the health of your pet fish. You need to know what can trigger various illnesses in koi, and what signs to look for. 

For example, it is paramount to provide your pet koi fish with a safe and clean environment. You need to make sure their pond is always kept clean, and temperatures are maintained at an optimal level.

Koi Sleepy Disease can be disastrous, and it should never be taken lightly. Symptoms of the illness include lethargy, swollen gills, loss of appetite, and sunken eyes. 

Experienced koi owners can differentiate between sleepy disease and a koi that is simply resting. However, this might not be as easy for newer owners. That is why it is important to stay informed, and talk to koi owners with more experience than you might have.

How Koi Fish Sleep in The Winter

You may have previously heard other koi raisers talk about how their koi hibernate in the winter. Well, the truth is, this isn’t entirely accurate. What koi experience during extremely cold temperatures is similar to hibernation, but not quite the same. Rather, koi enter a dormant state in the winter, known as torpor.

During this period, the koi will retreat to the bottom of their habitat. Even when they are awake, the koi will stay almost perfectly still. During the winter, a koi’s metabolism also slows down significantly, and they don’t grow nearly as fast.

Another important piece of information that all koi owners should know is that during torpor, a koi’s immune system gets weaker. That is why owners need to pay extra close attention to their koi pond during the winter.

Some koi owners believe in helping their pet koi fish enter torpor in the winter. Others prefer using artificial means to keep their koi pond warm, preventing their koi from going dormant at all.

Koi Fish Sleep Patterns Compared to Humans

There are a few animals whose sleeping patterns are quite similar to that of human beings, but koi certainly isn’t one of them. Adult humans need 7-9 hours of sleep to feel well-rested, while human infants can sleep up to 18 hours a day. Koi fish, on the other hand, don’t sleep nearly as long. Instead, they go into a state of rest for a few hours a day.

Are Koi Fish Nocturnal?

Some people seem to believe that koi fish might be nocturnal, but this isn’t true. The reality is that while koi do become active for a short period at night, they don’t stay active all night long.

Koi is a highly energetic breed of fish. They take short rests at different times of the day. Koi fish are usually most active right after sunset, after which they tend to rest again. When it turns darker throughout the course of the night, you’ll notice your koi settling into the bottom of their pond and going into a state of rest.

The sleeping habits of koi are also strongly influenced by their environmental conditions and other external factors. Their diet, the quality of their water, and temperature can also influence when koi fish become active, and when they start to rest.

Some experienced koi keepers have even been known to use these variables to artificially influence the sleep patterns of koi, in the hopes that it would allow them to grow faster, stronger, and even live longer.

Why Temperature Affects How Koi Sleep

Expert koi keepers know that there is an ideal temperature range at which pet koi fish will stay healthy and happy. This temperature is said to range between 59- and 77 degrees Fahrenheit. The temperature your koi are living in will influence many things, from their general behavior to eating habits, and even how they sleep.

For example, if the temperature drops below that ideal 59 degrees mark, your koi may become less active, and go into a state of torpor more frequently throughout the course of a single day. A good way to tell if your koi are following a healthy sleep pattern is to see if they become active during the early evening, just after sunset, as koi are supposed to.

Koi Sleep Patterns and Feeding

Your koi’s sleep patterns also determine the best time to feed them. This is because koi tend to be hungry when they are most active, but their metabolism slows down as they enter a state of torpor.

Most experts agree that the ideal time to feed your koi is from 10 am to 2 pm. However, if you find that your koi aren’t eating as much as they should, you may want to consider changing what time you feed them.

What is Apneic Sleep?

Koi and certain other breeds of fish are known to experience a form of sleep that experts refer to as ‘Apneic Sleep’. This means that when deprived of oxygen, some koi might enter a deep state of rest. During this rest, your koi won’t breathe at all. That doesn’t mean they are dead, however. As soon as they have access to fresh air, they will return to their lively, graceful selves.

Some vets and experts even go as far as to intentionally induce apneic sleep, to treat and medicate them without resistance.

Do Koi Fish Need Extra Light During the Night?

Some koi fish owners have wondered if their pet fish need extra lights at night. On the opposite end, some wonder if they should use artificial means to make their pond darker, so their koi might sleep better. Both of these practices are entirely unnecessary.

First and foremost, koi retain partial vision in darkness, meaning they can navigate their pond just fine at night. What’s more, these are animals that are accustomed to living outdoors. That means they don’t require any artificial light or darkness.

Why It’s Important to Understand How Koi Sleep

Koi fish owners need to have a keen understanding of their pet koi’s behavior when it comes to sleep, as this enables them to take better care of their koi. How a koi rests can tell you a lot about their overall health and quality of life, and can even help detect diseases.

Now That You Know

Now that you know more about koi fish’s sleeping habits, what do you think? If you’re an experienced koi keeper, do you already monitor your koi’s sleep patterns to keep track of their health? If you’re a new koi owner, do you intend to use the information in this guide?

If you’re looking to start your koi pond, it’s important to understand that raising koi is an immense responsibility. We encourage you to do plenty of research before committing to raising koi.

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