Do Koi Fish Sleep?

koi fish floating in water possibly sleeping

Koi appear stunning and magnificent with their gorgeous colors and mesmerizing swimming patterns, but within their beauty are many mysteries.

One typical mystery is… do koi fish sleep?

Koi appear to be awake all day long, and their eyes are always open, scanning for predators. But, while koi can not close their eyes since they don’t have eyelids, they are masters at deceit – they hide their resting time as an instinct to stay safe from predators.

Like all living things, rest is necessary for koi to recover. Koi fish do not sleep like humans but rather have short periods of rest where they float in a comfortable and safe spot.

Before they can rest in the pond, koi have to locate a comfortable area in the pond in which they will be safe from predators like raccoons or herons. This is often a central part of the pond or at the bottom. The bottom of the pond also has the coldest water.  Cool water slows koi’s metabolism so that they won’t be hungry. Which helps them rest. This is also how koi fish hibernate in the winter.

Once they’ve found their preferred location, they’ll float in the pond and rest. It may appear that they don’t move, but it becomes apparent that their fins make slight movements, and they hover in place upon closer examination. 

Here is a video that shows what to look for:

Notice the difference between rest and activity.  When koi are resting, they are kind of “out-of-it.”  When he first threw some fish food into the pond, the koi resting had no idea.  Once some sounds from the other fish alerted them to something going on, they joined the feeding party.  

How Long do Koi Fish Sleep For?

The resting periods might not be considered sleep the same way humans sleep. You won’t see a koi fish settling on the pond’s bottom dreaming for eight hours. Their “sleep” times are more like intense rest periods that replenish their body naturally.

Koi usually do most of their resting in the late evening to early morning. 

Do Koi Fish Sleep on Their Sides?

We know koi don’t sleep, float in a comfortable area, and rest. So no, koi do not sleep on their sides.

Sometimes, a koi that appears asleep on its side could be sick. A sick fish might appear uninterested or behave differently than fish asleep. So first, we need to be aware of what a koi’s behavior is when it’s asleep and then compare.

If koi begin to lay on their backs, it could indicate a problem. It could be a signal of several different infections. One is the Carp edema virus (sciencedaily.com), also known as sleepy koi disease (CEV/KSD), which is an infection first identified as an infectious disease and discovered in Japan around 1970. The affected fish are usually in the bottom of ponds, showing an extreme lack of energy. Common signs include skin conditions, sunken eyes, and swollen gills. The disease can alter the gill tissue in severe cases, lowering oxygen levels.

Are Koi Fish Active at Night if Not Sleeping?

Yes, koi are active at night.  While humans are asleep in bed for the night, koi stay active.  They may rest as stated above, but they are always in and out of activity. 

Do Koi Fish Need Light at Night?

No, koi fish don’t need light at night.  Like any other living animal, if you follow the cues from nature, everything will be good.  In nature, it is dark at night, which is the best for koi.  

Learn more about koi fish with this complete beginners guide.