Japanese koi group

Winter pond routines part 2 – Feeding

In the first instalment of this series I looked at heating during winter. Now it’s time to explore feeding routines, and in particular, whether or not it is a good idea to implement a fasting period. Just like heating, personal preference will have a big influence on the route you choose so my aim is to look at a couple of different scenarios and leave it to you to choose will is best for your koi.

Personally my views on feeding have always been the same – I think it can do more harm than good when the water temperatures are low. Whether you should feed or not will depend on various different factors and in particular how the koi have been kept during the summer.

Firstly, it is important to understand that you should never try to feed koi that are completely dormant. Regardless of what type of food you use the metabolic rate will have slowed so much that they will struggle to digest what has been given to them (if they will even take the food in the first place). Koi are quite intelligent in the sense that they will not go looking for food unless they know that they can digest it. So, if all of your koi are up at the top of the pond on a sunny winters day then they’re telling you they want feeding. This is where you should be responsible and follow three simple guidelines:

  1. Only feed if all of the koi are active. Make sure they’re at the surface looking for food, not just lethargically swimming around the pond.
  2. Don’t feed any more than once per day and make sure that all of the food is eaten within a couple of minutes. Any food left after this time should be removed from the surface.
  3. Make sure that you use a low fat food such as wheatgerm. Most winter based foods are around 4-6% fat, compared to summer growth foods which are often over 10% fat.

I’d like to touch on point three in greater detail because when koi are fed correctly in summer time they will build up a fat reserve which prepares them for their winter fast.

If they are then given a high fat content diet in winter this will further add to their body fat content which isn’t good for long term health. It can also lead to body shape problems, and although this can be corrected, the longer it goes on and the older the koi gets, the more difficult it can be to put this right. If you’re heating the water slightly I would still advise only feeding once a day to keep the koi ticking over, and still only use a low fat diet suitable for colder temperatures. It is not necessary to try growing koi over winter, after all that is what the summer months are for. Winter should be a time to recover the koi from the intense growing environment of summer, which leads me on nicely to my next topic: should koi be given a period of fasting during winter?

Water temperature will have an influence on how quickly koi burn off their excess fat. The warmer it is the faster their metabolism will be.

The point of fasting is to burn off the excess fat reserve and slim down the body, preparing it for the growing season the following year. Removing excess fat in this way can also help to purify the skin, especially the shiroji.

When a pond is set up to grow intensively during the summer and the koi are fed heavily it can be hard to keep the water in top condition which will impact on the fish. Their skin quality won’t be at its best, the shiroji can go off white, their heads turn slightly yellow and the pigmentation will generally soften.

Over the course of the growing season the aim is to gain as much length and volume as possible without making the koi fat. I plan to make koi a little bit bulkier than I would normally like to see, and then aim to get their body back to how I would expect it by the spring.

If your pond is set up in this way then I would strongly recommend a period of fasting, with feeding reduced gradually from the autumn into the beginning of the fasting period. The water temperature will have an influence on how quickly koi burn off their excess fat. The warmer it is the faster their metabolism will be, so getting the right temperature is important. I would recommend anywhere from around 7-12°C as stated in part one and the length of the fasting period will be decided by when you believe the shape that you consider to be ideal has been achieved – this could be anywhere from four to 12 weeks. If you don’t think your koi need to loose any weight, but you would like to give them a bit of a detox then between two and four weeks should be sufficient.

If your pond is left at an ambient temperature in summer and you don’t particularly push your koi very hard then there is probably no need to even consider a fasting period. The reduced temperatures and change in diet during winter will be enough to detox the body. In this case I would follow the guidelines at the start of this article and continue feeding the koi throughout winter whenever they’re looking for food – stopping feeding may actually lead to the koi being slightly malnourished and weak for the perils of spring time which lay ahead.

If you are heating the water slightly I would still advise only feeding once a day to keep the koi ticking over, and still only use a low fat diet suitable for colder temperatures.

Finally, a big ‘no no’ in my book is attempting to grow your koi intensively throughout winter, by this I mean replicating summer conditions with warm water and heavy feeding. Being in this type of environment for 12 months of the year can lead to a shorter life expectancy and will cause the pigmentation to deteriorate much earlier than would normally be the case.

When trying to rear high class koi the aim is to keep the skin quality good for as long as possible. In order to achieve this the skin must be given time to recover after each period of intense growth, this simply will not happen if you try and push them all the time. The only scenario I would deem growing koi over the winter to be acceptable is if you are rearing tosai that have missed out on a proper summer and you are using the winter to enable them to catch up with lost growth.


Look out for my final part of this series in the coming months. I’ll discuss making preparations for spring time and consider how to avoid the many problems that can arise when bringing koi out of winter.

Written by Ricky Stoddart

I am a koi fanatic and currently the managing director of Koi Wholesale Limited. I have been actively involved in the koi industry since 2001 and have been visiting Japan since 2002. Having gained a lot of experience, I've also been lucky enough to be able to learn from some of Japan's top breeders. As a result, I like to share my knowledge to help koi keepers and dealers get a better understanding of Nishikigoi.

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