Do Koi fish hibernate?

Last week we learned all the ins-and-outs about feeding Koi (if you haven't checked it out, you really should! It is a very cool info-graph) but, I found myself thinking 'What actually happens to Koi fish during the winter?'. I know most of us have known about hibernation since elementary school, but how does it work? 


Well, Koi fish actually go into a certain type of hibernation, called torpor, that allows the animal (or in this case, fish) to regulate their body temperature to acclimate to the air or water temperature. This is what allows them to survive when it gets below freezing. While in this state, even though it may seem like they are napping, they are really just slowed down. Torpor allows them to save energy by lowering their body temperature, decreasing their metabolism (they don't have to eat when in this state!), reducing their immune systems, reducing their breathing rate and reducing primary body functions. This also means that in places like Colorado, where the temperature can be completely different from the day before, your fish can come in and out of this hibernation like state. So, it's important to keep looking out for those warmer winter days and treat your Koi accordingly. These rare winter days where your Koi are active are a great time to treat them with Manda Fu food, which is specifically designed for Koi to eat during the winter as treats.

Something else to keep in mind is that it's important that you do your best not to disturb your fish during their temporary state of torpor and that you have a deicer active at all times during the winter. Even though your fish are in torpor, they still require oxygen to live, and if the pond freezes over no oxygen can get to them. Also, if your pond freezes over, that traps all of the natural gases released by any decaying matter at the bottom of the pond, which can be toxic to your Koi in high amounts.