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When do koi go dormant? | Decorative Ponds & Water Gardens Q & A

Q: When do koi go dormant?

Q: When do koi go dormant?

Helen – Minneapolis, MN

A: With winter officially starting in just one week, the cold weather is settling in across the country. Since your fish don’t have miniature submerged Koi calendars to check, what is it that tells your fish it is time to hibernate?

Koi are cold-blooded creatures, which means their body temperatures and activity levels are directly correlated with the ambient temperature. Koi are active and alert when their environment is warm and will start to slow down as the water temperature decreases. Once the water temperatures start to dip below 46°F your fish tend to stop eating and will retreat to the bottom of the pond. Your fish use the decrease in temperature along with the shortening day lengths as a trigger to prepare for winter.

As the water begins to cool, your fish will become less active as their bodily functions slow down. Less activity means a slower digestive process, less demand for food. It is this decrease in food digestion that warrants the use of wheat germ based foods like Pond Logic® Spring & Fall Fish Food. These types of food are easier to digest that regular food reducing the risk of leaving undigested food to rot inside a dormant fish, which can potentially be fatal.

As the temperatures continue to decline towards 40°F, the blood flow and respiratory rate of the fish will drop to an extremely low rate where their body is hardly functioning. You may hear people say that your Koi are sleeping in the winter and while fish do sleep this goes way beyond the standard drop in bodily functions associated with some much needed shut-eye. This extreme internal slow down ensure survival with even the most limited resources with cases of dormant fish lasting 150 days without food.

The whole over-wintering scenario sounds a little extreme to us but it is truly a natural and normal process for your fish. They do not require much attention in the winter but there are a few things you can do to ensure their winter break is a success. When a layer of ice begins to form over the pond, maintain an opening for gas exchange using an aeration kit or pond de-icer, like the PondAir™ & Thermo-Pond Combo.

Pond Talk: What do you do to help your fish through the winter season?

Vent Harmful Gases All Winter Long - Airmax® PondAir™ & Thermo-Pond 3.0 De-Icer Combo

8 Responses

  1. I watch over my pond for predators during the winter months while everyone could so easily be prey. Few years ago a weasel visited my pond, and they are terrific swimmers. In the dead of winter, this one made several trips into my natural pond. Although all my Koi were okay, a couple of my 30″ Albino catfish, perished.
    This year, all of the Albinos are hibernating right up front, close to shoreline in shallow water, rather than their 14 foot depth. As I’ve worked on the muck bottom for many years and the sand is finally showing through, it’s amazing to see them warming themselves against their new sandy bottom. They’re all huddled in together, in a neat row and it’s quite something to see nature working.

  2. I live in Virginia where some days in December can fluctuate into the mid and upper 50’s. Nights are still in mid to upper 30’s however. Can I feed my koi during these warm days or do I need to wait until spring when night time water temp is up too?

    • Hi Lew – Typically water temperature doesn’t change as quickly as air temperature and with the temperatures fluctuating daily it would be best to wait until spring to begin feeding again. It takes a little time for them to digest food and you do not want them to revert to dormancy with undigested food in their system.

  3. In the Sonora Desert in SW Arizona, they wake and go dormant off and on all winter. I know of several ponds around and it doesn’t seem to hurt them. The water temps vary up and down out here in the low desert of Arizona quite often so they don’t really ever go dormant. What is your take on this? The fish don’t seem to mind. Merry Christmas!

    • Hi Barbara – If the water temperatures hover around the cooler temperatures it may cause them to go in and out of dormancy. There isn’t to much you can do to change it but the fish will adapt to their environment and you should still notice that they feed less. Due to this fluctuation they may feed on algae or plants in the pond or you may choose to feed sparingly if receive a long stretch of warmer weather. Merry Christmas!

  4. TU I was told that when the pond water dips below 60 degrees to switch over to spring/fall food for the fish. Also when the pond water consistently is below 50 degrees to stop feeding them. That is what I have been doing since I out the pond in. I hope that is correct. Truly appreciate your tips. Ed

    Sent from my iPad


    • Hi Ed – The time to switch foods or stop feeding is somewhat subjective. We recommend to switch foods when water temps are between 40 and 50 degrees F, and stop feeding when temperatures are below 40. It will not hurt the fish to switch to a wheatgerm food sooner than 50 degrees. Fish will digest a wheatgerm food faster and may eat more of the food in a single feeding. Their feeding habits may also change as the weather fluctuates. Watch your fish and they will let you know if they are still hungry or ready for the winter.

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