Koi will eat other fish but it is not their natural behavior to do so. Koi are omnivores and will eat a variety of aquatic plants, insects, fish eggs, and other fish.
If you are just starting out on your adventures into the wonderful world of koi carp keeping then you might be considering adding other species into your koi pond
Koi can be quite expensive so mixing them with cheaper varieties of fresh water fish is an excellent way to reduce you initial start up cost for your fish.
In a large enough pond, koi will also grow to be quite big so mixing them with smaller species can be a good way to reduce the size of the pond that you will need once they reach full maturity.
Koi are generally considered to be a rather docile species as they were domesticated from the common carp many centuries ago.
They are not very aggressive or overly territorial and will generally get on with almost any other fish species that you may stock them with.
Stocking your pond with other smaller species will also add more variety into your pond and the smaller fish can be a nice contrast against the larger koi.
What Causes Koi to Eat Other Fish?
The three main causes that will result in a koi eating other fish are hunger, overstocking, and mistaking smaller fish for food.
Like any omnivore if a koi is not being fed enough they will resort to eating other fish which also includes their own fry and eggs.
You need to strike a balance when feeding koi so that there is enough food available for them to grow at a normal rate, while also not feeding them too much.
In winter koi will generally not be fed as their digestion shuts down once the water temperature drops below a certain point.
Also Read: How Long Can Koi Fish Go Without Food?
Overfeeding will also mean more waste in your pond and this can degrade the quality of the water.
This leads us into our next point, if your koi pond is overstocked then there will be competition for food and generally it is the biggest which will survive.
Over stocking a pond will naturally mean that the fish will have to fight in order to get the right amount of food.
In the wild one of natures ability to deal with over-populations is either starvation due to lack of food or cannibalism.
It is how large populations are kept in check and your back-garden pond is no different.
3. Mistaking Identity
Koi will often mistake smaller fish fry and eggs for insects and also artificial koi food that you may buy particularly if the pellets are brightly colored.
If a koi is used to feeding on pellets of a certain color then it is only natural that they may mistake little koi for food.
Koi will also eat tadpoles and frogs if they are present in your pond but they will not be a preferred source of food and will generally ignore the larger ones.
Will Koi Kill Other Fish?
Koi will kill other fish but it is normally as a food source rather than as an aggressive or territorial act, for style most part they are happy to live with other fish species providing that there is sufficient space and food available for the number of fish in a pond or koi fish tank.
They are naturally docile so any form of consistent aggression towards other fish is generally out of character.
Are Koi Fish Cannibals?
Koi are not cannibals by nature but if they have to they will eat other koi assuming that they are small enough to eat.
As outlined above it is generally rare but when it does happen it is either out of desperation or through a case of mistaken identity.
What Fish Can Be With Koi?
Freshwater fish such as any variety of carp or goldfish that matches the same PH and water temperature that koi are best suited to can live with koi.
As a general rule koi and goldfish can live together quite happily as long as the goldfish are of a big enough size so that they would not make an easy meal for the koi.
Some fresh water species should not be stocked with koi and these are predatory in nature.
Larger species of catfish will feed on just about any fish so if you are going to stock catfish in your pond then make sure that they will not grow to a size that would allow them to eat your koi.
You can also stock turtles in koi ponds but some species can be quite aggressive and will feed on both koi or goldfish if they are small enough.
Will Big Koi Eat Little Koi?
Big koi will eat little koi but only up to a certain size and will not do so out of aggression.
It is crucial to size your koi correctly in order to make sure that any new ones joining in the pond will be of a sufficient size that the established ones will not feed on them
Do Koi Eat Their Babies?
Yes koi will eat the young but only in rare cases, if they are hungry enough and often they will do so by mistake.
Very young koi fry will be quite small and to an adult may look like some of the aquatic insects that they are accustomed to eating on a regular basis.