Koi Fact Sheet
Can I mix goldfish and Koi together?
You certainly can, Koi and Goldfish essentially have the same requirements and will live quite happily together.
Can I put little fish with big fish?
Yes, once the babies have grown to at least 4cm, mixing the sizes of Koi and Goldfish is of no real concern, you may wish to ensure that there is plenty of food for the smaller ones, as big fish will out compete at feeding time.