Winter can be a confusing time for new koi keepers, especially due to the fact that you won’t be feeding your koi anything over the coldest months of the season. If you’ve kept koi for many years this practice will likely now be standard routine, but for newer pond owners it can seem quite unusual to stop feeding fish for such a long period of time.
Luckily, koi are quite resourceful creatures and can survive harsh winters without food due to torpor (commonly referred to simply as “hibernation”), a process that allows their bodies and metabolisms to slow down to a crawl, requiring only the smallest amounts of energy. This process is directly related to water temperature, and as the water temperature drops in winter, so too will their metabolism slow down alongside.
Once the temperature of the water reaches about 50ºF (10°c) your koi will likely be in full sleep mode, and you should have already stopped adding food to your pond. Koi will continue in this low-energy state, casually swimming around the middle of the pond (warmest point), until water temperatures begin to rise again in spring.
To note, feeding is just one aspect of getting a pond ready for winter, so be sure to check out our full winter care guide here for a complete winter pond checklist.
When to stop feeding koi in Winter?
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Koi should have already been well fed throughout the summer with a high-quality feed so they have a large amount of fat stores for torpor. You can then continue regular feeding during Autumn, whilst also monitoring daily feeding and water temperature. Koi are intelligent animals, and won’t just eat for the sake of eating, so as temperatures continue to drop they will begin to take less and less food each day. Monitoring feeding closely is important to reduce waste build-up left in the pond over winter, so you can gradually reduce feeding as koi begin eating less.
If temperatures remain fairly high during autumn, koi may be eating just as readily as in summer – and this is normal, so don’t worry! Remember, their metabolisms slow in tandem with decreasing water temperatures, not time, so you can safely continue feeding your fish so long as they’re eating what you give them.
As winter closes in, and water temperatures drop to around 50ºF (10°c), your koi will no longer take food and their bodies will slow down as they begin hibernating/torpor. In most cases, feeding can be stopped completely around 55ºF (13°c) to minimize any waste leftover, but even if there is a little leftover food it won’t likely cause any major problem so long as the pond is well filtered and maintained. After this point you cease all feeding over Winter until Spring arrives and water temperature begins to rise again, and then you gradually increase the dose alongside the warmer temperature.
Water temperature can easily be determined using a floating pond thermometer, which can be kept in the pond all winter. We recommend either Danny’s Thermometer (pictured) or Laguna’s Floating Thermometer as they’re both durable, easy to read, and offer both Fahrenheit and Celsius readings.
Should I use wheatgerm food in winter?
- Hikari Wheat Germ 4.4Lb Medium
- Hikari Wheat-Germ Is A Highly Nutritious, Easily Assimilated, Highly Digestible Daily Diet For Koi And Other Pond Fish
- It will have your aquatic pet looking their best while improving their fertility.
Plant-based protein feeds, such as wheatgerm, are a popular choice for cold weather feeding as they’re more easily digested and release energy at a more gradual rate compared to regular feeds. With that said, they also generally contain less protein, amino acids, and often have lower palatability – which means your koi may not like it as much!
The biggest problem with cold weather feeding isn’t the type of food you’re feeding, but the amount you’re feeding your koi. Any excess food will contribute to waste build-up, which is detrimental to hibernation/torpor as it can cause issues with water quality over winter. Wheatgerm-based feeds will be no different from regular feeds in this regard; with both contributing to waste levels if the food goes uneaten in the pond.
Personally, I feed my koi with high-quality “summer” feeds all year without any problems. Carefully monitoring your fish during feeding when the weather gets colder, and adjusting the amount you feed based on their eating activity, is more important than whether you give them wheatgerm feeds or not. If you still want to try a wheatgerm feed, we recommend Hikari’s Wheat Germ products as they’re high in protein and have good nutritional profiles.
For a full list of the top foods for koi we recommend, check our dedicated article below:
Will left over food rot in my koi’s gut over winter?
This is an age-old myth that just isn’t true, as there is no scientific evidence to suggest that matter left in a koi’s gut will rot while they sleep. When water temperatures hit 50ºF (10°c) koi will likely stop taking food, when water temperatures hit 40ºF (4°c) koi will slow down even more – but even at this extremely low temperature, their body still functions normally.
This state does not mean all bodily processes stop, it just means they slow down so less energy and resources are required for each individual function – which is why it’s technically it’s called torpor, not hibernation. Just like a koi’s heartbeat, a koi’s gut will continue to slowly process food and will also still house good bacteria essential to keeping the system in balance.
The gut acts as an active bio-dome, encouraging beneficial bacteria and discouraging harmful bacteria that could potentially cause problems. As well as this, at temperatures as low as you see most winters, koi become active refrigerators and do not present as the ideal environments for rotting food (quite the opposite).
To conclude, any leftover food will not rot inside your koi during winter, so you can safely keep feeding until your koi stop eating or water temperatures drop low enough – whatever comes first!
During Early Winter – Treat For Parasites & Infection!
A final point to take into account, and something that is covered in our full winter care article is treating parasites and infections before water temperatures get too low. This is common practice during the start of winter and spring, as this is when koi are the most vulnerable to infection due to their lower immune systems while in torpor. Treating your pond for a wide range of parasites, as well as bacterial infections, approx 2 months before water temperatures reach 50ºF (10°c) will ensure koi are protected into spring.
As a general rule, we suggest treating the pond for both parasites and bacterial infections as soon as daily feeding starts to be reduced, as this indicates the start of a slowing metabolism. For parasites we recommend Aqua Med’s Aqua Prazi and for bacterial infection API Pond’s MelaFix treatment. These can be used together in both winter and spring for maximum protection during torpor and the best kick-start to the new year.
any experience with dropsy in your koi ?
Hi Ann,
Apologies for the delayed response! I will pass your comment along to someone who has more experience with dropsy than I do! In the meantime, we do have a pretty detailed guide on identifying, treating, and preventing koi dropsy if you’d like to read it here: https://pondinformer.com/how-to-treat-dropsy-koi-carp/