This is a vast topic which is covered here only as it pertains to breeding in Utah.

There are many sources on the inter-net that cover this subject very thoroughly. This is just a brief synopsis. Koi breed in Utah when the water warms in early June to as late as early August.

When the water warms around 65, you usually need only put something in the pond for them to lay eggs on, and they will spawn. It's very coincidental that the availability of water hyacinth and the breeding season come at the same time. I've never had mature koi that didn't spawn within a week of placing hyacinth in my pond, so try that. Mop heads tied together sometimes work, too. After placing this medium in the pond, if your fish are interested, you'll probably see them 'cleaning' it the night before they spawn.


Get up early the next day or you may miss it. The breeding age of a koi is four years. The females tend to be plumper while the males are usually thinner, more streamline. The best way to tell is on breeding day, when the males began chasing the females. By bashing into her, they provoke her to began laying eggs, which they in turn fertilize.

Your water can get quite frothy during this stage, and the whole process has a distinct odor all it's own. After the eggs are laid, if you intend to raise the fry, you need to remove the eggs at once, or barricade them off somehow so your fish don't eat them. Which they will. Those smaller fish chasing the female are probably not interested in breeding as much as they are getting an extra meal. Only a few out of every hundred eggs has the potential to be a great fish, and none of them will be considered anything other than domestic koi.

Keep that in mind. You can't possibly keep them all, so you'll have to cull them. If you don't have the stomach for this, don't even try. It's very possible that if you do nothing, a few babies will survive anyway. I had about 30 survive all on their own last year, and some turned out very interesting and still reside in my pond.

see also Koi Eggs and Raising Fry