Koi are some of the most common and visually stunning fish that can be kept in ponds. These sometimes very large fish are descended from the Common carp, and are closely related to Goldfish. However, unlike Goldfish, Koi need to be kept in outdoor ponds in the backyard rather than in tanks and require a different type of care compared to aquarium fish.
This eye-catching variety of fish was originally bred in Japan as an ornamental fish, but began to become widespread in the US and Europe in the 1900s. Koi will do an excellent job at brightening up an outdoor water feature, but what do they eat? How should you feed them to ensure optimum health? Koi are omnivores and require both plant and animal matter in their diet. The primary element of their diet should be protein-rich, for example fish-meal. They also require carbohydrates which can come in the form of grains such as wheatgerm. Vegetables, fruits and some other items can be given to them as treats. They can be hand-fed which is a fun and interesting way to train them, and inspect their health.
Here, we’ll dive deeply into the world of Koi, focusing on their feeding habits and dietary requirements. We’ll take a look at the diet of Koi and their relatives in the wild, as well as providing guidance on how and what to feed Koi in your pond.
First, let’s discover exactly what a Koi is…
What Is A Koi?
Technically, Koi are brightly colored varieties of the Amur carp (Cyprinus rubrofuscus) (see a video of a wild Koi here!) which have been bred for their color and used as ornamental fish in ponds and water gardens. Originally, around the 5th century, Amur carp were domesticated as food in East Asia due to their hardiness and ability to survive in a range of conditions in freshwater.
Japanese farmers used to raise the carp in their rice fields for food purposes, but their interested began to change when they noticed mutations in the fish which produced stunning coloration. At the beginning of the 19th century, people in Japan began to breed Koi. A range of color variations were established from red to white, yellow and blue, and many patterns combining multiple shades and tones. Nowadays there are more than 100 officially recognised varieties within 16 groups. Some notable examples include:
- Kohaku – white base colour with orange-red markings. One of the original ornamental varieties that were bred in Japan.
- Showa Sanshuko – black base colour with white and orange-red patterns.
- Taisho Sanke (or Taisho Sanshuko) – Similar to the Showa Sanshuko, but with a white base colour and black and orange-red markings.
- Hirenaga (or Butterfly) – characteristically elegant, flowing fins (below).
Most Koi varieties can grow up to 2 or 3 feet (60-90 centimetres) and some even larger. The life expectancy of a healthy Koi can be 20 to 30 years. Shockingly, the oldest recorded Koi was 226 years old when it died! Their ideal water temperature ranges from 59 to 77 degrees F (15-25 degrees C).
Keeping Koi is now a worldwide hobby, and many people with ponds or water gardens consider them a first-choice fish. One disadvantage of their bright colors is that they stand out clearly to predators such as herons, mink, raccoons, otters, foxes, and cats, and this can be a problem if they are not sufficiently protected.
What Do Koi Fish Eat?
Koi are essentially omnivores – they will consume both plant and animal matter. The food items they consume depend largely on the environment they live in, and whether they are wild or captive. We’ll have a look here at a Koi’s wild diet compared to a captive Koi’s diet.
What Do Koi Eat In The Wild?
In the wild, Koi – or more correctly, Amur carp – are incredibly opportunistic, eating just about anything they can get their fins on. They are not fussy about the food they eat, and will take everything including:
- Plant materials such as aquatic plant leaves
- Insects and insect larvae
- Small fish and fish eggs
Many wild Koi will sift the bottom of a water body, searching among the mud and silt for food. The fleshy barbels either side of their mouths are used to feel for food as they scan the base of their freshwater habitats. In some places, wild Koi will actively hunt for insects or other items floating at the surface of the water. When they catch live prey, they will take it into the mouth and crush it down into a soft pulp for swallowing, as they have no teeth.
Their dietary elements will be informed by the type of habitat they live in and what can be found there. Amur carp search for food both day and night, and spend time resting or hiding at the bottom of the water when not actively hunting for food.
What Do Captive Koi Eat?
In naturalistic and usually large-scale ponds, also known as ecosystem ponds, Koi can be left to their own devices to forage and hunt for natural food sources. This system needs to be well-monitored to ensure the fish can obtain enough food, and a big enough variety of food for them to thrive without help.
However, most ponds and water gardens in domestic settings are either too small or more focused on the ornamental element of keeping fish and maintaining a water body. Therefore, most captive Koi will need feeding.
It is possible, and very common, to buy specialised Koi fish food. This can come in many forms including:
- Flakes – these tend to be the best form of food for smaller Koi and their fry (baby Koi).
- Pellets – it is ideal to look for pellets that can be swallowed whole, as Koi cannot chew them.
- Bars – this form is ideal for larger individuals, but smaller Koi may also nibble at the edges
Koi can be very entertaining to watch when they are fed – they become excitable and animated, and therefore it can be fun to offer them food which floats. This is also an advantage when you need to monitor the amount of food your fish are eating, and their overall health. Sinking food it also an option but does not allow you to get a good look at your fish.
When thinking about the content of the fish food, you should choose food which is rich in protein. Koi require 32-36% of their diet to be made up of protein-rich foods like fish-meal, shrimp-meal, and whitefish. Secondly, they require a carbohydrate element which can be composed of wheatgerm, soybean meal or corn gluten – these are often accounted for in specialised Koi fish food.
The amount of food you feed to Koi fish will depend on factors including the number of plants growing in your water body, the stocking density, the age and size of the fish.
It is common to provide captive Koi with blue-green algae (cyanobacteria) or spirulina algae. These come in pellets or tablets, and are free-floating. Fish fed on these will show increased growth rates, improved immunity and digestion, enhanced coloration, and a host of other benefits.
Some other key rules to keep in mind when it comes to fish food include:
- Low phosphorus – feeding Koi food with a large phosphorus content, or excess food can impact water quality and increase the amount of algal growth. This can cause problems for Koi health and extra issues for you to sort out.
- Nutrients and vitamins – Koi benefit from supplements incorporating calcium, and vitamins A, C, D, E and K.
- Fat content – Koi require between 3 and 9% of their diet to be made up of fat.
See a video of a Koi feeding frenzy here!
Supplementary Feeding For Koi
As a treat, Koi can be fed a variety of fruits and vegetables, which have to be carefully prepared, including:
- Broccoli and cauliflower, leek and garlic, squash, and leafy greens like lettuce, spinach and endives. All vegetables should be cut into small pieces, try to make them the size of Koi pellets.
- Melon, grapes, kiwi, strawberries, and citrus fruits like oranges and mandarins. Fruits tend to be softer than vegetables so do not need to be cut into tiny pieces. Slices should suffice for most fruits.
- Extra sources of carbohydrates like pasta, rice, oatmeal, and wholewheat bread. These should be given carefully in moderation, as they can be fattening for Koi. Items like rice and pasta should be cooked until soft, and salt should not be added.
Avoid any food with dressings, sauces or flavorings – Koi do not need these! And they could even be toxic for them.
For some further ideas and inspiration, take a look here.
What Should Koi NOT Eat?
You should avoid giving Koi wheat grains, and white bread. Food items that are high in carbohydrates can cause problems for their stomachs.
Any fish or insects you have caught should not be offered to them. These carry the risk of disease and parasite transmission.
Koi also find peas very hard to digest, so it is best not to include these in the vegetables you feed your fish.
How Should You Feed Koi Fish?
As a general rule, if your pond has few or no plants, your Koi should be fed for up to 5 minutes, 3 or 4 times per day. It is good practice to throw the food in, one handful at a time. When the fish start to leave food rather than snap it up instantly, you can stop feeding. Any excess food left in the water should be removed using a net – this removes the risk of lowering the quality of the water.
The more often you feed you fish, the more familiar they will become with you. It will then be easier to train them to take food directly from your hand. But do not be tempted to overfeed them! Little and often is the key here.
In an ecosystem pond, Koi can be fed just twice a week, with only a handful of food.
When Should You Feed Koi Fish?
Koi require different kinds of feeding, or types of food during different seasons. During early spring and late fall they favour more carbohydrate-rich foods.
During summer they will become most active, grow more quickly, and raise their metabolic activity in preparation for the breeding season. They require more protein-rich food during the warmer months.
Winter is a different story – Koi will hibernate, and their metabolic levels will drop very low. They do not require feeding at this time of year. You should start to feed your Koi again once the water temperature reaches 65 degrees F (18 degrees C).
Summary – What Have We Learnt About Koi?
Koi are stunning and interesting varieties of fish. They are opportunistic feeders, taking everything from algae and plant matter, to insects and other fish. Captive Koi in garden ponds and water gardens must be cared for responsibly and given a varied diet with the right components for the Koi to thrive. They require a diet high in protein, with a element of carbohydrate, fat and essential vitamins and minerals.
Koi can be fed on specialised Koi fish food which incorporate the essential items they require in their diet. Supplementary feeding can include fruits, vegetables and some more carbohydrate-rich foods. These should be cut into small pieces or slices, depending on the hardness of the food, and fed in moderation. They should not form the main part of a Koi’s diet. Hand-feeding can create a bond between fish and owner, and feeding time can be a very enjoyable experience.
It is important to research how to care for your Koi fish carefully to ensure they are as happy and healthy in their watery environment as possible! Always consult an expert if questions or issue arise in terms of the care of your Koi.