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What do you really mean when you say fish are “dormant” for the winter? Do they sleep? | Decorative Ponds & Water Gardens Q & A


Q: What do you really mean when you say fish are “dormant” for the winter? Do they sleep?

Q: What do you really mean when you say fish are “dormant” for the winter? Do they sleep?

Diane – Wells, ME

A: When the days shorten and temperatures drop, koi and other pond fish enter into what’s called torpor, or a period of decreased physiological activity that allows them to save energy. They don’t sleep the winter away, but they do essentially hibernate—their metabolism slows, they require less food, their activity level drops and their body temperatures reduce.

How do they know they need to hibernate, and what can hobbyists do to make their finned friends’ winter torpor restful? Read on to learn more.

Mother Nature’s in Charge
Fish don’t use calendars to decide when to take their winter snooze. Instead, they follow Mother Nature’s lead. Because fish are cold-blooded, their metabolism reacts to the external environment. When the water temperature falls, so does their activity level: Their appetite dwindles, they digest food more slowly, and they expend less energy. In the spring when temperatures warm back up, the fish will naturally come out of their torpor. They’ll start to seek out food as their metabolism increases, and they’ll become active once again.

Suspended Animation
You’ll know when your fish go dormant. They won’t lie down on the pond’s bottom or curl up in their cozy Koi Kastle, but they will float upright, tuck in their fins and remain suspended in the water. As the fish hover there, you may still see some super slow movement, and they may also wind up facing in the same direction as if they were heading somewhere at less than a snail’s speed.

Sweet Dreams, Koi!
Here are four ways to give your koi a peaceful winter rest:

  1. Set up an aeration system to keep the water pumped full of oxygen. Even though they’re hibernating, your fish will still need some fresh O2.
  2. Install a de-icer to keep a hole open in the ice and allow for gas exchange. If the pond freezes over, use warm water to reopen a hole; do not bang on the ice to crack it, as doing so can stress your fish.
  3. Keep as much debris out of the pond as possible to prevent muck buildup over the winter.
  4. Let the fish be. Don’t try to get them to move or swim or wake up from their slumber. Keep an eye on them, but leave them alone until they wake up on their own.

Pond Talk: Have your fish started hibernating yet?

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6 Responses

  1. thank you

  2. I have just shut my Koi pond (water garden) down for the winter and installed the aeration. The temperatures are still mild and fish still swimming around. Should I continue feeding?

    • If temperatures are still above 40 degrees you can still feed but I would test with just a few pellets first to see if they are even interested in feeding. If they are you can continue but I would recommend only giving a small amount especially with the filtration turned off.

      • My rule is: no filtration, no food. Otherwise the waste has nowhere to go, and the water becomes polluted and the koi become stressed, to say the least. I just closed my pond (water 43°F, day ambient 64°F, overnight ambient 38°F), but stopped feeding them 3 days ago. I did a final 15% water change yesterday, and added AquaMedZyme Winter Blend, which controls amonia, heavy aeration not required, though I am running two air pumps, one which has a battery back-up. It’s not cold enough for the de-icer yet, but it’s getting there. I run a Tetra 500W that looks like a little spacecraft. You can tell it’s working by the light on top. It’s very reliable, which is what you MUST have when the pond freezes over.

  3. I live outside Dallas TX where we have very moderate winters. It may be below freezing for a couple of days and then can go back up into the 70’s, even 80’s. I have started feeding your Spring and Fall food but I’ve always wondered if my koi ever really go dormant. IE it is 11/12 and we are just dropping into the 70’s with our lows in the 50’s yet our days are much shorter. Any advice?

    • Hi Betty – You stay much warmer that we do up here in Michigan. If you only have a few days where temperatures are below freezing chances are your fish will keep on going. Water temperatures take longer to drop than air temperature. It would take consistent cold temperatures in order for the water temperature to also drop. You can always get a small floating thermometer and keep and eye on the water temperature for feeding purposes. You fish will also give you clues as well, if they still move fairly rapid when you approach the pond they are still ready to go. If they move very slowly and are not interested in feeding or acknowledge your presence than their systems are slowing down.

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