Are Koi Fish Active At Night?

Koi fish are very active during the day, but what about the night? So are koi fish active at night? Let’s find out.

Koi are active at nighttime in the early evenings; this is a natural time for koi fish to be active because, in nature, this is the time they typically begin searching for food. As the night progresses, the koi fish will settle again – they are not active the whole night through. 

Koi fish are known to be very active fish. If you have ever seen them, you will know that they are often on the move. If you are thinking of adding some koi fish into your pond, you have come to the right place! Read on to learn some exciting koi fish facts.

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Are Koi Fish Active At Night?

Koi pond at night

Yes! Koi fish are active at nighttime. However, they are not active the whole night long. 

In general, koi fish are very active than other pond fish. They are constantly moving but also have short moments of rest. When the sun has just set, the koi fish is known to be the most active during this time. 

Koi fish are most active in the early evenings because, in nature, this is prime feeding time. Around evening time, planktonic organisms rise and feed off the pond’s surfaces, attracting insects to the water’s surface. These insects entice the koi to the surface for a delicious snack!

As the night progresses, the koi may settle at the bottom and rest due to the lack of light. They are not commonly highly active all night long but will be active from dusk and into the evening for a few hours. 

Although it is common for koi fish to be active at night, this is not always their most active time. The time they are most active is dependent on a combination of the time of day and the temperature of the water. 

How Does Water Temperature Affect Koi? 

The temperature of the water can affect the activity and metabolism of koi fish. 

In general, koi fish will be pretty active when the pond is warmest during the day, usually between 10 am and 2 pm. 

There is an ideal temperature at which koi fish need to function at their best. The perfect temperature for koi fish is 59 to 77 degrees Fahrenheit. 

When the water temperature drops below 59 degrees Fahrenheit, the koi fish will become less active. Regardless of whether it is nighttime or not, the koi fish will not be as active in cold temperatures. In winter, a ponds’ temperature drops relatively low so, sometimes having a heater is an excellent idea to keep them functioning correctly. 

Koi fish become less active in the cold due to their metabolism. Their metabolism slows down in these cold temperatures and, when they have a slow metabolism, they slow down too.  

If your koi fish are usually quite active in the early evening, that’s a good sign that the ponds’ temperature is right. If not, it may be time to install a heater! 

Feeding Koi Fish When They Are Active 

Taking note of when your koi fish are active is a good indication of when they are hungry. Overall, koi fish need feeding once a day between 10 am and 2 pm. 

As mentioned previously, it’s a good idea to feed koi at this time because they will likely be pretty active. The pond’s temperature will be at its warmest, and, therefore, the koi will be moving around! 

It is vital to note that the amount you feed them does depend on whether it’s warm or cold. As mentioned earlier, the colder temperatures often leave koi less active due to their lowered metabolism. 

Below is a temperature and associated feeding guide: 

  • Below 70 degrees Fahrenheit, but above 65 degrees: Feed once a day. 
  • Lower than 55 degrees Fahrenheit: Do not feed. The koi metabolism will be very low at this level, and they will not eat.
  • Between 76 degrees and 82 degrees Fahrenheit: Once to twice a day. Be careful not to overfeed. 

Please note that when the koi fish are in much warmer water, they will be very active. Koi fish owners often overfeed highly active koi fish as they assume they are constantly hungry, but excess food in the water will affect the water quality, which could affect the health of your koi. 

Do Koi Need Light At Night?

Koi fish

Many people notice their koi becoming active at night and wonder whether they should have some light near the pond for their koi. 

Koi fish do not need light at night. All fish need periods of darkness, as this is the closest imitation of their natural habitat. It is best to avoid placing any artificial light in or around your pond. 

Ideally, koi fish should have around 8 hours of darkness and then 8 hours of daylight to function normally. 

Koi Fish Sleeping Disease

Koi sleepy disease is a highly infectious disease that spreads among koi fish. It is also known as sleeping sickness, and its official name is the Carp Edema Virus (CEV). This virus leads to inactive and lethargic koi fish, hence “sleepy disease.” 

This type of infection has a high mortality rate in koi fish, so it is wise to take note of its signs and symptoms. Early intervention can help save the infected koi and prevent the disease from spreading to the rest of your koi. 

Signs of Carp Edema Virus (CEV) 

  • Lethargic 
  • Lying at the bottom of the pond, commonly on their side 
  • Swollen gills 
  • Lesions on the skin around the mouth and fins 
  • Cloudy eyes 
  • White fungus 

Carp Edema Virus commonly affects young koi as they have a weaker immune system. Most koi breeders will inoculate their koi against this virus; however, outbreaks can occur. 

If one of your koi presents with any of the above symptoms, it is vital to get it to the vet as soon as possible to provide it with early treatment. 


In conclusion, koi fish are active at night, as this is their natural time to come out and search for food. However, how active a koi fish is, depends mainly on the temperature of the water. If the water is cold, koi fish will be less active and require less food. Furthermore, you should not place any artificial light in your pond as koi need an 8-hour day and night cycle. 

Overall, koi are happy and active fish, but noting the signs of Carp Edema Virus is vital if you have koi. This virus is treatable, but it can spread across the pond if left alone.


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