The warm weather is obviously the best time to be able to enjoy pond fish keeping. During this time pond fish and koi are active, lively, and highly visible. Many pond fish and koi become downright interactive with their keepers and will follow them around the pond, stick their faces out of the water or practically climb out of the pond to celebrate feeding time. During this time we all know exactly what is going on with our fish and all it takes is a quick peek into the pond.
Then the cold weather sets in and we slowly lose our ability to see what’s happening with our pond fish. Their activity slows down, they tend to keep themselves concealed, and once the ice and snow come; well, we lose touch with our fish. So what’s going on underneath those layers of ice and snow? What are our fish up to?
In short our fish are not up to too much. But pond fish not being up to too much is an interesting behavior all the same, given that they are so lively throughout the rest of the year. Koi and pond fish are poikilothermic animals, a fancy way of saying cold-blooded. This basically means that their body temperature is regulated by the surrounding temperature of the water, and their body functions respond and change according to the water temperature. The activity and metabolism of koi and pond fish is greatly reduced which is why they do not feed during the cold periods. Many experts say that because koi and pond fish are cold water fish they actually benefit from a cold period, however; prolonged cold spells are not good for them, they run the risk of their immune systems actually shutting down.
So what do they do? For the most part they sit on the bottom of the pond in the “warmest” pocket of water they can find. During winter months the warmer water is on the bottom of the pond as opposed to warmer months when the warmer water is at the top of the pond. I have often seen my koi lined up next to each other, facing the same direction as if they were in a parking lot! This is funny behavior that may lead to think that they are huddled together to share body heat; but since koi are poikilothermic that would not make sense, so this behavior is probably a way to fit as many koi into that pocket of warm water as possible. In larger warm areas you’d probably see a more random formation of the koi, some facing this way and others facing that way.
What happens to the koi and other pond fish is that they go into a state of torpor. Torpor is not quite full hibernation, because it is of a shorter duration than hibernation, but otherwise it is a very similar state of being: reduced body temperature, slowed metabolism, slow reaction times, reduced breathing rate and primary body functions. Torpor allows the animal to save the energy that would otherwise be needed for higher levels of activity. Because of the state of being in torpor it is a very good idea to keep things as calm as possible around the pond. If you need to open the ice in the pond find a quiet way to do it like using boiling water to open a hole, don’t chop it open with a pick ax! Even using a hand held drill with a hole saw is actually pretty quiet compared to other methods, and if the ice is too thick to open with boiling water the hole saw is a great tool to have. To maintain an open area in the ice try using a floating de-icer or an aerator. This open area in the ice will allow noxious gases, like ammonia, to escape from the pond.
Some people add salt to their ponds. I personally am not a practitioner of adding salt unless it is for treatment purposes, but if you do add salt to your pond you should dilute your salt levels during cold winter months. The salt can make your pond water’s freezing point drop to below 30F which will kill your fish. Generally speaking you should not let your pond water’s temperature drop below 34F. Temperatures below 34F will allow ice crystals to form on the gills of your koi, which can kill them, so watch the temperatures if you live in an area of extreme winter temperatures.
If your pond is cleaned and prepped prior to those cold dark winter months, then worry not, your koi and pond fish should do just fine. Like was mentioned the koi, goldfish, and pond fish in your pond do not DO much during the winter months. Spring will be here soon enough and your fish will start again with their antics and amusing behavior. But for now you have a better idea of what is happening out there under the ice and snow, and you are not missing out on any party. If only we could share that state of torpor and wake again when the spring has sprung!
The LOVE YOUR POND blog is written by Mike Gannon of Full Service Aquatics. Mike is a professional pond builder and expert in the broad topics of fishkeeping and water gardening. Mike also produces THE POND HUNTER video series which can be viewed on Youtube. “In The Pursuit Of All Things Aquatic” the Pond Hunter videos provide how-to pond construction videos, pondumentaries, and videos of related interest. Mike resides in Summit, New Jersey with his wife and 2 daughters. To visit his website go to www.loveyourpond.com and visit The Pond Hunter at www.youtube.com/thepondhunter. All copyrights to this material belong to Mike Gannon.