Do Koi Fish Hibernate? All You Need to Know!

Koi fish do go into hibernation mode in winter. However, it is different from other animals as they exhibit unusual signs.

Read on to find out more about Koi fish and their hibernation period.

Do Koi Fish Fully Hibernate in the Winter?

There is no definite answer to knowing if Koi fish go into total hibernation in the winters or not.

This is because, during winters, Koi fish become semi-dormant. This can’t really be called hibernation though.

But for ease of reference, let’s call this lethargy stage and hibernation only.

Koi fish are not alone in this. There are many other pond fishes that enter this lethargy instead of going into full hibernation. In this state, called Torpor, Koi fish need NOT be fed.

Because of the reduced metabolism from cold temperatures, Koi fish will suffer from bloating and other digestion issues if they eat food. This can even prove fatal to them.

How Long Do Koi Fish Hibernate?

Koi fish usually hibernate for around 3-4 months. However, this can differ from fish to fish, as some are known to hibernate for longer periods of time.

When the water temperatures start to rise again, you will notice your Koi fish becoming more active and looking for food.

This is a good indication that they are coming out of hibernation and are ready to be fed again.

What Happens to Koi Fish During Hibernation?

Below are some of the changes you will notice in Koi fish when they go in hibernation.

They Rest in Upright Position

When Koi fish hibernate, they rest at the pond’s bottom in an upright position. In this phase, they tuck their pectoral fins beneath their bodies.

The pectoral fins of Koi fish are responsible for their movements, like sideways and up and down.

The tucking of pectoral fins allows Koi fish to maintain their upright, sitting position. Furthermore, the Koi fish is also able to float from one place to another.

Arrange themselves in a Line

During hibernation, Koi fish will move towards the bottom as the temperature will be warmer. In the summer season, this is the opposite. Water near the bottom of the pond becomes cooler.

Sometimes, Koi fish will arrange themselves in a line when they are about to hibernate. They may also have even spacing between each other.

This is because Koi fish are trying to take the optimum amount of space in the warm water. If kept in a  bigger pond, they are more likely to be dispersed at random locations.

Metabolism is Reduced

In their hibernation state, the metabolism of Koi fish is reduced, especially when the water temperature falls below 50 degrees Fahrenheit.

At this temperature, you will need to feed them twice or thrice every week.

Continuous reduction in water temperature will require your own discretion as to what their feeding schedule should be. At 40 degrees Fahrenheit, they don’t need to be fed as they will in hibernation.

In hibernation, Koi fish won’t respond to any significant water changes. You, however, have to make sure that the water quality is kept pristine throughout the entire hibernation period.

Immunity Goes Down

Just like metabolism, the immune system of Koi fish will have low effectiveness. This makes them highly prone to various diseases. Hence, they require a lot of extra care.

Apart from their own immune system, Koi fish are also vulnerable to many parasites and bacteria that will become active in the winter season.

However, Koi fish owners shouldn’t worry too much. If the Koi fish have completely hibernated, the bacteria and parasites will also be less active, given that they have the same environmental conditions.

You should, however, be careful for your Koi fish health whenever you see a noticeable shift in the water temperature.

At What Temperature Do Koi Fish Hibernate?

Koi fish will start to hibernate if the water temperature falls below 40 degrees Fahrenheit. The ideal temperature for their hibernation is a little above the freezing point.

If the water temperature reaches freezing, Koi fish will not be able to survive.

Even if a portion of the Koi pond or fish tank is frozen, Koi fish will hibernate and have good health, provided that there are areas where water is in a liquid state.

How to Care for Koi Fish in Hibernation

Here are some of the things you can do to take care of Koi fish when they are in hibernation.

Check the Water Temperature

Whenever you are nearing the winter season, it is best to keep a thorough check on the water temperature of your Koi pond or fish tank.

Since we know Koi fish will become semi-dormant below 40 degrees Fahrenheit, you will be better prepared for it. Make sure the pond is kept in good condition always.

Reduce Feeding Your Koi

By the time you notice the water temperature is nearing 45 to 40 degrees Fahrenheit, you need to start reducing their feeding times.

At 45 degrees Fahrenheit, you should completely stop giving them food at all.

Contrary to how this may sound, this is actually for the Koi fish’s own benefit. In such low temperatures, their metabolism is reduced, making digesting their food a problem for them.

It may come off as a surprise, but Koi fish can actually survive without food for a long time, especially in the winter season.

Move Your Koi Fish

In case you fear that your Koi pond will get frozen, it is best if you move your Koi fish to individual fish tanks or even an indoor pond.

This will protect them from the harsh winter season.

Once you have got them inside, you can reduce the water temperature to encourage them to go to their semi-dormant state.

This is preferable as you can easily watch and take care of them.

When Do Koi Fish Come Out of Hibernation?

Koi fish come out of hibernation when the water temperatures start to rise and become stable. This happens mostly in late spring or early summer.

You will know that your Koi fish are coming out of hibernation when they start to become active and look for food more frequently.

You should, however, not feed them immediately as they might not be able to digest the food properly. Wait for a few days and then slowly start feeding them according to their appetite.

As the water temperature starts to rise, you will also see them swimming around more often. They will also become more vibrant in color.

How to Keep a Koi Pond Warm in the Winter

There are a few things that you can do to make sure your Koi pond is warm throughout the winter.

You can use a pond heater to raise the water temperature. This is, however, not recommended as it can be quite expensive and may overheat the pond or fish tank if you are not careful.

Another way to warm up your Koi pond is to use a floating pond de-icer. This will help to keep a hole open in the ice so that gas exchange can take place and your Koi fish can breathe.

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It is also important to make sure that your Koi pond is well insulated. You can do this by using bubble wrap or a pond cover. This will trap heat and prevent the water from freezing over.

Many people recommend having a Koi pond deep enough so that the Koi fish aren’t affected by the freezing conditions. Ideally, your pond should be 4 feet deep so that the surface water gets frozen quickly.

You should also consider moving your Koi fish to a heated indoor pond. This is the best way to keep them warm and safe during the winter months.

Finally, one more method of keeping a Koi pond warm is to make sure it is thoroughly aerated. Aeration will ensure a steady supply of oxygen as well as keep the water temperature high enough.

Can Koi Fish Survive Without Food in Winter?

Koi fish can survive without food in winter as they go into a state of semi-hibernation. In this state, they do not need to be fed as their metabolism slows down, and they do not have an appetite.

It is, however important to make sure that the water quality is maintained throughout its duration as Koi fish are still susceptible to diseases.

When to Start Feeding Koi Fish After Winter

You should start feeding your Koi fish after winter when the water temperatures start to rise and become stable. This usually happens in late spring or early summer.

You will know that your Koi fish are ready to be fed again when they become active and look for food more frequently.

Start by feeding them small amounts of food and gradually increase their intake as they start to digest their food better.

Signs That Your Koi Fish Are Ready to Hibernate

Koi fish usually start to become less active and sluggish in the winter as the water temperatures start to drop.

They will also stop eating as their metabolism slows down, which reduces their appetite. You might also notice that your Koi fish start to change color as they prepare for hibernation.

When the water temperatures reach around 50 degrees Fahrenheit, your Koi fish will start to enter into a state of semi-hibernation.

It is, however important to make sure that the water quality is maintained during this time as Koi fish are still susceptible to diseases.


Koi fish need to be taken care of when they enter their semi-dormant state.

Their low metabolism and appetite require you to stop feeding them. You must make sure that the Koi pond is in good condition.

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