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

Why is my Koi not Eating its Food? Guide to Fixing Eating Problems 2018

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

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 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 topor 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 if 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:

  • Poor quality feed & nutrition
  • Poor water conditions
  • Stress & unhappiness
  • Sickness or parasites
  • Injury (I.e, Predators)
  • Sudden drop in water temperature

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?

Just like us, koi will gradually become bored of their food if it’s not to their standards!

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 natural in their diet; ingredients that can be found in good quality feeds. These include: High protein from aquatic source (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, or a sudden change in environment, are common reasons koi may lose interest in food.

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 water temperature reaches around 50ºF (10°c), however, koi will stop eating completely as their bodies will be all but shut down for hibernation – 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

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 which 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

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/topor 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)

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 topor 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 when High Quality Feed 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 gases 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.


2 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.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.