Why Are My Koi Carp Not Eating? (And How to Fix It)

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Why Is My Koi Not Eating Its Food? Guide to Fixing Eating Problems 2022

how often should koi eat
During summer koi should be eating very regularly, so if they stop it could be a sign of a growing problem in your pond. Public domain.

A koi that stops taking food can be a concerning sign, but it’s not always something you need to worry about. Koi carp, just like many other freshwater fish, do not have static eating patterns throughout the year, and will change their feeding behaviour based on their environment. The amount of food a koi will take is actually dependent on water temperature, and you’ll likely see your koi eating much less in early spring and winter when it’s colder, but taking lots of food in summer when it’s warmer. This is the koi’s ever-changing metabolism at work, which speeds up in warmer weather and slows down in colder weather – eventually leading to a full torpor state, commonly referred to as “hibernation.”

As well as this, koi may just be getting bored of their food and have nicer snacks to eat around the pond, especially if you have plenty of plants. They may also be feeling a little under the weather that day and may not be interested in eating, which is normal, but if the behaviour continues for more than a few days it should be investigated further. Below are some of the more common reasons your koi may stop eating their food, with some problems being more serious than others.

Common reasons why Koi stop eating:

Koi carp that are sick, injured, or living in poor water conditions are less likely to take food and will likely need some care and attention to fix the underlying issues. In this article, we cover numerous reasons your koi may not be eating, as well as provide solutions to improve their happiness and appetite.

Do koi get bored of their fish food over time?

koi can become bored of their food over time
Just like us, koi will gradually become bored of their food if it’s not to their standards! Public domain.

One of the most important aspects of koi keeping is making sure you’re feeding your fish the best possible diet to keep them healthy, strong, and interested in their food. Low-quality fish feeds generally contain a lot of ingredients that koi don’t need, and not many ingredients they actually do – and they can tell!

This causes problems with excess waste build-up, weakened fish, and koi which eventually grow bored of the food in general. Just like us, koi have a complex range of taste buds and like to eat certain things that come naturally in their diet; ingredients that can be found in good quality feeds. These include high protein from aquatic sources (i.e., fish meal), low ash content (waste/filler), and a good vitamin & mineral profile. Making sure the food you’re giving your koi is both tasty and nutritious will improve their eating habits and overall health!

Will a sick or injured koi stop eating food?

When a koi is sick, either from bacteria, parasites, or injury, they’ll naturally break away from the group and seek a quiet place in the pond. During this “downtime” period they’ll try to recover and are unlikely to be interested in food or treats. Depending on how serious the illness or injury is, this may only last a few days, but it could last weeks. If you suspect a fish is sick or injured and they’ve not come up for food for a few days, you should consider treating the fish for both parasites and infection, as well as giving them a hands-on inspection.

Losing interest in their food is one of the first signs of a poorly koi, so if this happens to your fish it could be a sign they’re feeling under the weather. Most of the time they’ll recover on their own, but it’s often better to give them a helping hand for maximum peace of mind.

None of my koi are eating any food – what should I do?

poor water quality impact on koi feeding
Poor water quality, or a sudden change in environment, are common reasons koi may lose interest in food. Public domain.

The most common reason for a group of koi to all stop eating at once is a sudden drop in water temperature, usually around late autumn or early winter. A koi’s metabolism is directly related to water temperature, so as the pond cools down, so does a koi’s appetite. Even though this process is usually gradual, with koi taking less and less as winter draws close, a sudden change can also cause koi to stop taking food for a few days as they get used to the shock. This is normal and shouldn’t be a problem so long as they start eating again after a few days. Once the water temperature reaches around 50ºF (10°c), however, koi will stop eating completely as their bodies will be all but shut down for torpor – again, totally normal!

Another reason a group of koi may stop eating, and something more serious, is a sudden change in water quality. Koi are very sensitive to changes in their environment and a sudden spike or drop can cause all sorts of stress. Keeping a koi’s environment as stable as possible is important, and any sudden (or gradual) changes can cause them to eventually stop eating altogether.

How to Improve Feeding & Solve Common Koi Eating Problems

1) Fix Problems with Water Quality

pond master water quality test kit
Testing water for problems may help determine a cause for koi losing interest in food.

As with so many other problems, poor water quality can cause koi to lose interest in their food over time. Koi are very sensitive animals, with sudden spikes or drops being very dangerous and stressful. Since it’s difficult to determine if water quality is the problem visually, the best way to investigate is to use a pond water tester kit that provides results for a range of measurements. When testing water you’ll want to pay close attention to readings for ammonia, nitrites, pH and KH, as these are the most common to cause problems with appetite.

Both ammonia and nitrites are very toxic to koi, and are a by-product of waste decomposing in the pond. Most of the time your pond’s beneficial bacteria population will be enough to keep ammonia and nitrites in check – a process called the Nitrogen Cycle. Sometimes, however, there may be a sudden spike in these substances, or even a gradual rise over time, where beneficial bacteria isn’t able to keep up with breaking them down. In cases such as this, and if your tests come back with medium-high ammonia levels, you should work to lower these before your fish become sicker.

As well as ammonia and nitrites, both pH and KH are important measurements which need to be kept within certain parameters. Rapid changes in pH are deadly to koi, and changes in KH can influence pH as it acts as a natural buffer in the water. Water with a high or low pH, or a changing KH, can cause koi to become stressed and sick so they lose interest in food. For further reading on how to test water, and how to improve quality, check our dedicated articles below:

2) Provide a Tastier (Better Quality) Feed

hikari gold koi food
If your koi are being fussy about their food, you may want to consider trying a different feed – we recommend Hikari Gold.

If you suspect your koi may have become a little bored of their food you can try switching to a different brand or a better quality feed. Koi can be fussy, just like us, so a change in taste may be all they need to start eating again!

In terms of food, we recommend a feed high in protein (35-40%), with the protein coming from a primarily aquatic source. Cheaper quality feeds will have protein from plant-based sources, such as wheat and corn, but this isn’t ideal for koi carp. A more ideal source would be fish meal, krill meal, or anchovy meal – all of which are aquatic-based protein sources which koi prefer in their diets.

As well as protein source and percentage, making sure the feed is low in waste content (ash) and high in vitamins and minerals is a must for a healthy fish and pond. Vitamins A, B, C, and D are all important to a koi’s immune system and health, with vitamin C being particularly beneficial. Fat content should be kept around 3-10%, with a higher content being better for younger koi or for packing on some weight ready for winter.

On top of a new feed, you can also try feeding your koi a variety of natural and healthy treats, such as silk worms, meal worms and other insects. These are very high in fat, so you shouldn’t over feed, but your fish will almost certainly love them in small doses!

For food we recommend Hikari Gold Koi Food as it is high in fish meal protein and has a great nutritional profile. For treats we recommend Hikari’s Silkworms, which provides high fat content, extra shine, and will help keep koi interested in their grub.

3) Treat for Parasites, Infection, and Injury

Treating for both parasites and infection is recommended if you believe your koi isn’t eating due to sickness.

A sick or injured koi will be much less likely to take food compared to a healthy koi, and sometimes it’s difficult to know what exactly is wrong (if anything). Fish can become sick from common parasites, or infections, and can also be injured around the pond or by predators. Unless you handle your koi regularly and know what you’re looking for, it’s unlikely you’ll know for sure if parasites or injury is the primary cause.

With that said, most parasites and infections are easy to treat, so it’s often best to apply treatments if you notice signs just to be sure. Some common signs of parasites or injury to look out for are: 1) Sluggish movement, 2) Not eating food, 3) Losing color, 4) Visible sores or injuries, 5) Hiding away from group.

Even if you’re uncertain of the exact cause, it’s often best practice to simply treat the pond with a wide-range parasite and injury treatment to ensure you have everything covered. Most koi keepers will choose to do this at least twice a year anyway; usually at the start of spring and end of autumn. This gives koi a strong head-start to the year and a much safer hibernation/torpor period so they’re not at risk of parasites or infection. For parasites we recommend Aqua Meds Prazi Treatment, and for injury/infection recovery we recommend API Pond’s MelaFix treatment.

As well as treating for these problems, you should also make sure to try to reduce the risk of them happening in future. Injury is often caused by predators, and parasites are sometimes brought by pests, such as ducks. For more information, you can refer to our dedicated articles below:

4) Get Ready for Winter! (So They Eat Come Spring)

benefits of pond heaters deicers
A de-icer will help gas exchange take place over Winter, which can help koi become active again come Spring.

A final reason koi stop eating, and one which often worries new koi keepers, is the build-up to winter. Unless you understand how torpor works, it can be quite a shock when your fish stop taking food as weather gets colder; but luckily this is completely normal! Most pond fish will slow down their eating during autumn, and completely stop taking food when water temperatures hit 50ºF (10°c). During this time koi will begin slowing down and will be able to survive off their fat stores they’ve gained from summer feeding. Even though there isn’t much you can do to make your koi eat during winter (they really don’t need to!), there are still things you can do to make winter more comfortable for them and improve their hibernation period. These include:

  1. Adding a Heater/De-icer for Gas Exchange
  2. Adding an Air Pump for Oxygen
  3. Cleaning sludge, muck, and reducing waste
  4. Feeding High Quality feeds in Summer
  5. Treating for Parasites and Infection during Autumn
  6. Adding a Fish Shelter for them to Hide

All of the above points will help winterize a koi pond and make it safer and more comfortable, even during the harshest winters. If your pond freezes over, adding a de-icer for harmful gasses to escape is almost essential, and providing extra oxygen via a dedicated air pump is highly recommended alongside. Feeding koi with a quality feed during summer ensures they have plenty of fat stores to be happy during winter, and cleaning out as much waste as possible keeps ammonia and nitrites low all season.

Even though these will not make your koi eat during winter, it will improve their condition come spring and speed up their “wake up” period so they start eating faster in the New year! For a full in-depth guide to taking care of your pond in winter, refer to our guide on this here.


25 thoughts on “Why Are My Koi Carp Not Eating? (And How to Fix It)”

  1. My koi have not been eating for a while. They seem to have lost weight. i feed them a high quality food. They are active and look healthy. but concerns me that they eat very little. i’ve tried to treat the with mealworms, but they aren’t interested. This started after their spawning. I didnt do a water change because of the frye. I just did water change. hopefully they will start to eat!

    • Hi Geri,

      Spawning can be quite a stressful period for koi, so it may take them some extra time to ‘unwind’ and get back to normal afterwards. As well as your water change, you could also try adding some activated carbon to your filter box which will help remove excess pheromones (and any other organic pollutants) that are still lingering in the water as a result of the spawning.

      I would also recommend you perform a broad range water quality test to make sure your ammonia, nitrites, pH and KH parameters are in good standing.

  2. One butterfly koi I have doesn’t know how to come to surface to eat floating pellets, while others are able to do so. He often stays on bottom sucking gravel and spitting. I tried isolating him to lower water level bucket and he managed to eat some, what are his problems?
    *They were recently brought in.

    • Hi Jay,

      This behaviour can actually be fairly common, especially for fish not yet accustomed to their new environment. In the wild, carp will browse for food primarily along the lake/pond bottom, as this is both safer and more natural to them. In a similar way, newly introduced domesticated carp may decide to feed on the pond bottom until they’re certain their new home (and food delivery method) is totally safe. As well as this, koi will have different personalities and preferences, with some always being more skittish than others and needing more time to adjust to major change. So long as your koi isn’t loosing weight, color, or acting strangely outside of eating off the pond floor, I’d say just give them a little more time!

      Also, to help speed things along, try to make sure that minimal food is going to waste and sinking, because if the fish continues to associate the floor with food, it may not decide to ever eat from the surface as it can just as easily obtain food below. Once it realizes both you and the environment are not a threat, and the floor isn’t so nutritious after all, it will likely start to eat with the others in future.

  3. All my goldfish and koi just stopped eating one day and haven’t ate in two days and they keep staying on top of the water opening there mouth and closing fast .is this a sigh of low Oxygen?

    • Hi Kyle,

      Yes, that could very well be a sign of low dissolved oxygen, but it could also be another issue, such as general poor water quality or high water temperature. The only way to know for sure would be to pickup a water quality test kit for both dissolved oxygen and general parameters (ammonia, nitrites, pH, KH etc.) and see what the results show. I’d say you should try to do this asap, as it does sound like it could be an issue with water quality, whether oxygen, ammonia, or a combination of many things!

  4. Hi there. I got two small Koi last fall, both about 2″ (now currently ~5″ and 3.5″). I put them in an existing 20 gallon tank and did frequent water changes to keep up with the smaller tank size. I was feeding them leftover Omega One sinking goldfish pellets, along with lettuce/spinach and mealworms as treats. I recently moved and they spent about 48 hours in a 5 gallon bucket with an aerator. I got them set up in a new 45 gallon tank, and although agitated, they are eating the sinking pellets fine. In my research into how to move them, I realized there is Koi specific food (and I feel like a total idiot). I got a bag of the Hikari Gold; however, they will barely touch the pellets. If a pellet happens to be directly in front of them, they’ll eat it, but otherwise they continue to swim around. I gave them some spinach to test if it was a floating vs. sinking thing in the new tank, but they ate the spinach fine.

    My question is if the Koi food is way better for them than the goldfish pellets, and if so, do I just keep trying to feed them the floating pellets and eventually they’ll get it? Or can I continue feeding the GF pellets?

    The GF pellets have the same CP, more fat (10 vs 3), slightly less fiber (3 vs 5), and a lower ash content compared to the Hikari Gold. Thank you!

    • Hi Devan,

      Goldfish pellets should be perfectly fine, especially for juvenile koi. Both koi and goldfish are in the same family (cyprinidae) and although some niche ingredients may differ (i.e., colour enhancers more common in koi feeds), the core ingredients are essentially the same as their requirements as a species are very similar.

      With that said, the biggest difference you’ll notice when using goldfish feed vs koi feed as your koi grow is that of the impact on your wallet! Once your koi grow past that of a goldfish, they’ll need more food and, preferably, bigger pellets so none accidentally go to waste. It would be very expensive to continue feeding goldfish pellets at this point, so a switch to a larger koi feed would be logical.

      In terms of the goldfish feed you’re using, arguably it’s a better choice for now, anyway! Young fish will benefit from higher fats, and personally, I’d say 6-10% for juvenile koi is ideal for optimal growth. So yes, you can continue with the goldfish feed without issue, but you may want to switch to a koi product when they get a little bigger and start demanding more!

  5. How long can koi go without eating. I recently had to get in the pond in order to patch a hole in the liner and they haven’t eaten since. I think they are mad at me. How do I entice them to eat?

    • I have several Koi fish in a pond. The biggest one has stop eating and he jumps up out of the water. He has never done that before. He hasn’t departed from the other fish and I don’t see any signs of injury.

  6. Hi

    ive just built a new pond and have got 5 koi i it. they dont seem to be eating and it looks like im about to loose one. he has been on his own for a couple of days looking like he is gasping for air. the others although i havent seen them feed seem to be ok.
    i have a PH level of 7.5 and the water seems to be ok.

    • Hi Ian,

      If the koi are gasping for air, it sounds like the pond may be lacking oxygen and/or the water is too warm. Do you have any form of aeration in place, such as fountains, waterfalls, air pumps? What are your other water quality parameters showing – in particular, ammonia, nitrites, and nitrates? Finally, what type food/brand are you feeding them?

      Koi newly introduced to a fresh pond often require an acclimation period where they need to become used to the environment and changes in water quality from their stock tanks. In my experience, this can differ greatly between koi, with some feeding and acting normally almost immediately and others needing several weeks before they feel comfortable.

  7. Hi we have some Koi (3 large and the other smaller). We added 5 new ones this year and they behaved a little strange and 3 died at once within a few months with the last two dying yesterday. The symptoms are not eating, staying in the edge of the pond and opening their mouth and gills a lot. The pond is well aerated. It seems as though one of our original large Koi is now doing the same thing and we want to try and save it, any ideas what this could be? The rest of the Koi seem to be behaving normally.

    • Hi Sophie,

      I’m sorry to hear about your fish loss! Never an easy thing.

      That’s also a tough one to figure out without actually seeing the pond and fish! To start though, could you let me know your general water quality parameters, such as ammonia, nitrites, nitrates, pH and KH (alkalinity)?

  8. Hi,

    I just brought 6 new butterfly koi, 4 are eating well and enjoying the new environment. However, another 2 koi are not adapting to it and is getting skinnier each day, almost able to see their bone structure.

    We had separate this 2 into another tank so that they can have their quiet space and recover their own as all other koi are very active. But after separating them they are still not eating, what else should I do?

    • Hi Lisha,

      I apologize for the delay in responding!

      This is a bit of a difficult question to answer without seeing the fish, but first and foremost you should check your water quality parameters (pH, dissolved oxygen, ammonia levels, etc.). In addition, do the fish that aren’t eating display any other potential symptoms, such as acting sluggish, having sores on their body, any changes in scale coloration? If your water quality is healthy and your fish appear otherwise unharmed aside from being thin, I suggest trying a different food. Sometimes fish, just like us, can get tired of eating the same things over and over again. A tastier, but still nutritionally well-balanced, diet may be all that they need.

      Hopefully your fish are doing better by now! But if not, give those suggestions a try.

  9. Hi. I recently added 8 koi to my pond where I already had 4 strong fish. Three days later, after they had acclimatised, all but three of the new fish died overnight. Water temp is fine; pH is fine; no logical reason to find. If I introduced bacteria with the new fish, why did three of the new batch survive?

  10. Please help!

    My koi is not eating, spitting out food after putting them in his mouth. He was all good till one day he knocked onto the sides of the fish tank and got kind of injured.

    We used to have a few kois in the tank but we realised that they are too big now and the tank might be too small. The previous one passed away after being severely injured from knocking onto the sides of the tank. We are thinking of giving the koi away to someone who has a pond but it seems like it’s refusing to eat now and we don’t know what to do.

    • Hi Xq,

      I’m sorry to hear that! How long ago was your koi injured? Are you able to tell how he is injured/are there any visible injuries? Any other symptoms other than not eating?

      As this has occurred before with another fish, I would say your tank is too small and the koi don’t have enough room to swim around as they would like to. I would advise moving them into a larger tank or, better yet, into a pond where they will have plenty of space. You can also try feeding more enticing things for now like fruits (citrus, watermelon, etc.) and veggies (squash, spinach, shelled peas, etc.) to see if he shows more interest in those things.

      Best of luck, and I hope that your koi heals soon!

  11. Hello
    I had my five koi twenty years ago, sadly one by one they have passed away. I was left with two up until 3 weeks ago when one passed away leaving my little girl on her own. Neither had come out of hibernation properly as had not started showing signs of eating. My little girl was then hiding in a corner and clearly was stressed, she got white spot…then my ph crashed! I got the ph up, through a water change and naturally, believe it or not by putting cockle shells through my food blender and adding. I then had to counter the white spot so after 24hrs I added FMG. Its been 4 days now and she just won’t eat. She comes to my hand but is just not interested in food. I think she is missing her companion. What do you think? Thanks H

  12. I have a 2500 gallon pond it is new. filtration is always running. After 2 weeks i added 3 fish to the pond. I dont see them were did the go? The pond is 4 feet deep.

    • Hi Jim,

      How long has it been since you’ve seen them? fish can often be shy and stressed as they adjust to their new environment. They are more than likely just hiding somewhere, and should come out on their own in time.

  13. Hi there I have a bit of a problem I have 4 gold fish 3 in long and one koi 8 in long, I brought them in for the winter in 40 gallon tank and the koi has eaten 2 times in a month and gold fish 4 times a day I can get him to eat water is fine ph is 8 or higher some days water is changed every month and I have to bubblers, he swims fast around the tank and seems to have a lot of energy for not eating, also the water tamp sitting at 73f 23c. Any help would be appreciated thanks


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