When winter rolls around there is a lot for koi fish owners have to do to keep their colorful fish comfortable until spring comes, but what do koi fish do while the world is frozen over? During winter koi fish go into a kind of hibernation, called torpor which is esentially hibernation caused by a change in temperature, that leaves them nearly motionless as they conserve energy. When koi go into this hibernation a koi fish's metabolism, immune system, and even their bodily functions change.

The perfect koi products for winter

• The Essential Book of Koi: A Complete Guide to Keeping and Care | Learn from experienced international aquarists on how to best care for your koi fish in the winter months.

• Aquascape 39000 Pond Heater and De-icer for Pond Water | Helps with proper gas exchange during winter months to keep koi fish healthy.

Metabolism

Because food is usually very hard for a fish to find during the winter in order to preserve energy a koi fish's metabolism slows dramatically in cold temperatures. This is the reason why you do not have to feed your koi while the pond's temperature is under fifty two degrees Fahrenheit, in fact at that temperature koi do not show much interest in eating even if you present them with food. In order to preserve even more energy koi fish also barely move during their partial hibernation. They will only move enough to keep their joints from freezing while staying near the bottom of the pond.

Immune System

Throughout the winter koi fish's immune system also slows to a crawl, and this is actually what posses the biggest threat to your koi. When winter ends, the parasites and bacteria which can cause your koi to become sick actually become fully active well before your koi's immune system comes back online. This leaves them especially vulnerable to sickness after winter is over. While slowing down their immune system does allow koi to conserve energy through the winter and stay fairly safe, it can be dangerous once the weather changes so keep an eye out when spring comes!

Bodily Functions

By now you have probably sensed a pattern, during winter the koi fish slows everything down and their no bodily function is an exception. They slow down their breathing to conserve energy as well as make up for the lower amount of oxygen in the water due to ice cover. their blood moves more slowly through their bodies due to the cold temperatures which is likely one of the things that trigger the koi fish's hibernation-like state. Even their digestion slows, but since they do not eat much (if at all) during the winter that is to be expected.

Over all it is amazing the adaptions koi fish make to survive during harsh winters. Between slowing their metabolism, nearly shutting down their immune system, and reducing the speed of their bodily functions they clearly show off their hardiness when they "hibernate" during the winter. However it is important to look after your hardy pets, because even though they are tough if the water gets below thirty five degree's they could still die because of the cold.

Were you as surprised by the changes koi fish make during the winter as I was? Do you have any stories about your koi fish during the winter? Are you going to have your first winter with koi fish this year? You should check out our article about winterizing your pond  before winter roles around.