Wintering your Koi

by Chip Borkenhagen

Koi, Comets, and Shubunkins are amazing fish. All are basically related to our common carp, which is not indigenous to the United States but ubiquitous in almost every river, stream, and lake in Minnesota. A hearty fish that can reach 30 to 40 pounds, the Koi have been prized in Asian cultures for many centuries. Comets and Shubunkins are typically recognized as our good old goldfish. But all three species can be bred as multi-colored and many-patterned fish. Their coloring makes them especially appealing in ponds, which typically have dark bottoms and lower light.

Ponding in Minnesota—while a very cool hobby for many reasons—can be tricky. With only five or so months of reliable weather, and the necessity of putting our ponds “to bed” each fall, it can be difficult taking good care of our valuable finned friends. I have two Koi who each must weigh somewhere around 5 to 7 pounds. Through the years they have become pets, and good winter care is essential.

Each fall—around October 15th -30th, we wrangle all the fish together. We sort out the adults from the newly hatched babies. The babies are shared with friends, who usually need to feed them and keep them in an aquarium through the winter. The adults are another story.

These fish have the amazing ability to virtually shut down their systems if given the right circumstances. In our cool (50 degree) basement, we fill a horse tank with cold water to within 5 or 6 inches from the top. We put the fish (20 or so) in the tank, put in a “bubbler” for oxygenation, place a cardboard lid over the top, and leave them quietly alone until the following spring (April, usually). I say quiet, because they actually do go into a sleep for these winter months. If they are disturbed, they tend to want to eat, and the last thing we want to do is feed them because their digestive systems have shut down; if they do eat, the food rots in their stomachs and soon we call them “floaters.” Not a term one wants to use to refer to your Koi, especially if you have 10- or 15-year-old prize beauties.

Koi can be kept successfully over the winter right there in their pond, but usually a heater and industrial strength bubbler are in order. Frozen Koi don’t even float!

As mentioned earlier, Koi are hardy fish, and if the pondmeister pays attention, with good planning and organization, they will be delighting you for many years to come.

Here’s a start for learning how to winterize your pisces pals.

Nishikigoi

The Pond Doc

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