Being a natural omnivorous koi fish will eat a large variety of foods such as algae, aquatic insects, surface insects, animal matter and plant matter.
Most ponds will not provide koi with enough food so you will have to substitute what they are able to forage on with a high grade commercial koi food.
Like most fish their diet will vary throughout the year depending on the season and what types of food is available in their habitat.
One surprising thing about koi is that they do not have a stomach, instead food passes through their digestive tract which is roughly two to three times the length of their body.
Koi digestion times are heavily dependent on the kind of food and more importantly the water temperature.
The colder the water temperature the slower koi will digest their food.
Once temperatures get below 7 Celsius or 44.5 Fahrenheit koi will stop digesting their food.
This can pose a danger to the koi as undigested food will rot in their intestine and there is a risk of a bacteria causing an infection.
This is the main reason the koi keepers do not feed their koi in winter.
If you have a heated pond however this may not apply, assuming you can keep the water temperature above a safe minimum threshold level.
High quality food leads to higher quality fish.
What Do Koi Fish Eat?
1. Commercial Koi Food
The best thing to feed your koi is a high quality koi food mix which usually come in pellet form.
These commercial mixes are specially formulated to give the koi all of the nutrients and protein that they need in their diet.
Different foods can be purchased that are designed to increase the growth rate of your koi and others are available that will enhance the color of your koi.
As stated above it is highly unlikely that a garden pond could sustain a population of adult koi.
Even in a very large well established pond with lots of vegetation and insects present the amount of food needed to sustain a mix of large koi and younger growing koi is too much.
Also Read: Can Koi Fish Live in Tanks?
Almost all koi keepers understand that they will need to feed their koi a commercially available koi food.
Koi breeders feed their koi several times a day to maximize growth rates and they can only do this by buying the very best koi food available.
Koi will feed on algae in a pond, although it is not their first choice and will only do so if their is no other foods available.
Because algae is easy to digest they will feed on it during winter months when their digestion has slowed down considerably.
Like any member of the carp family koi will feed on insects, both sub-aquatic and almost any insect that will land on the surface.
In their natural environment they will routinely feed on insect larvae that live in vegetated waters.
Koi will also end small frogs and tadpoles if your pond happens to have them, once the frogs reach a certain size most koi will leave them alone.
Also Read: How Long Can Koi Fish Go Without Feeding?
They will happily eat meal-worms, earthworms, spiders, flies, moths, and crickets.
One word of cation with feeding koi insects is that some insects such as beetles or slugs will feed in plants that have been treated with pesticides so be care full as they may end up poisoning your koi.
Koi will love to feed on shrimp and other crustaceans as they will form a part of their natural diet in the wild.
Just be a aware that you should not catch any kind of wild crustacean from a local river, stream, or creek as they may carry some form of bacterial disease which could easily kill your koi if it got into your pond.
Your safest bet is either cooked shrimp that has been allowed to cool or dried shrimp that you can buy in any pet store or online.
Vegetables make a great koi treat with some of the favorite being lettuce, broccolli and garlic. Just be mindful not to feed then too much as from a nutritional stand point something like lettuce will not contain a lot of nutrients.
As a general rule it is fine to fee koi vegetables twice a week as a treat.
Koi absolutely love to snack on fruit. I generally prefer to feed them fruits that will float so that any uneaten items can be cleaned off with the help of a net.
Watermelon and grapes are two of the best fruits to feed koi as they really seem to love them particularly on a hot summers day.
Most fruits are quite acidic in nature so just like the vegetables best to give as a koi treat twic eper week.
7. Other Koi Treats
Boiled eggs, oatmeal, cooked wholegrain rice, whole wheat bread and even cheerios are perfectly fine to feed your koi but please do so in moderation.