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.
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:
- 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.
- 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.
- Keep as much debris out of the pond as possible to prevent muck buildup over the winter.
- 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?