When the temperature drops your koi, and other pond, fish enter into “Torpor” a period of decreased activity that allows them to save energy. They don’t sleep the winter away but the do hibernate. They let Mother Nature take charge and follow her lead. When the temperature drops so does their activity level and appetite / digestive process. They kind of go into “Suspended Animation” meaning they will float upright, tuck in their fins, and remain suspended in the water. Sort of like HOVERING in the water; you may see some super slow movement and they may all wind up facing in the same direction moving at less than a snail’s pace.
Sweet Dreams Koi, to help them rest comfortably: 1. Set up an aeration system to keep oxygen pumped into the water. 2. Install a de-icer to keep a hole open in the water allowing gas exchange. 3. Let them be “DO NOT TRY TO MOVE THEM; MAKE THEM SWIM; OR WAKE THEM. Keep an eye on them but don’t bother them.
For more details or if you have questions look up “The Pond Guy” @ www.thepondguy.com