To Heat Or Not To Heat

This article was first written for and published by Koi Magazine in 2009

Koi are cold blooded animals and their body temperature is approximately 1 degree C above the water temperature that they live in. They traditionally come from Japan which, because of its geographical location, suffers extremes of weather conditions – hot summers and very cold winters.  In the Niigata region there can be snowdrifts of 4 metres deep.  It is thought that carp originate from the Caspian Sea in Asia and again this region has a similar climate to Japan.  This history of Koi (“Koi” in Japanese simply means “carp”) shows that they are suited to living in areas where they have to endure at least one month or even more under ice.  “Ahh!”, I hear some of you say “We are not talking about Koi here, but Nishikigoi!”.  Yes, that is true so let us look at the history of Nishikigoi and why heating water has become popular.

 During the winter months, because the fish’s’ metabolism is related to water temperature ( the colder the water, the slower the metabolism), they don’t grow.  For a Koi farm, this is not good as the fish are not increasing in value.  So, for commercial reasons, farms in Japan started heating indoor systems in the early 1990s – that is less than 20 years ago! Dealers and hobbyists travelling to Japan saw this and thinking it was a great idea, sought ways to heat their own ponds.  Heating systems were taken from the swimming pool industry and cobbled into Koi ponds – this really took off in 1993 to 1995.  Just because Koi farms heat their ponds over winter though is it essential for hobbyists to do the same?  Are there benefits or even adverse effects to heating your own Koi pond and if you don’t heat, will your fish suffer?

Reasons to heat : 

 1. Fish remain active throughout the winter and continue feeding and also growing, providing more interest for the hobbyist.  The closer the water temperature to 18 degrees C and above, the more active the Koi’s immune system is.

2. Heating is good for faster development of small Koi, increasing their chances of achieving “Jumbo” size later in life.

 Reasons to not heat:

 1.Covering your pond to retain the heat can make your garden unsightly and makes it difficult to observe your fish.  This can also create an environment which can drastically reduce your pond’s PH value and water chemistry. (Any disease works faster in warm water so observing fish it is really important to pick up problems early.)

 2.  It is thought, by some of the UK’s fish scientists and Koi keepers and most top Japanese Koi breeders, that fish over two years plus need winters to go through the seasonal development of eggs for spawning.

 3. Heating your Koi pond is very expensive!

If you want to grow your fish big, and money is no object, heating your pond is a great way to enjoy the hobby.  If you just want to appreciate your fish and relax with them, and you are prepared to wait for your fish to grow, then don’t heat your pond – it will not only save money but a large amount of hassle setting up covers and worrying about fuels bills and the health of fish that you can’t see under the covers. The fish’s immune system is compromised over winter in cold water, but if you prepare the fish to be bug free in the autumn and maintain the filters throughout the winter then the fish should come through with no problems.