Have questions about baby koi?
A popular topic is “how do koi spawn?”
The female koi will get “rushed” by the male koi. She will usually get chased by two or three males, and she will get wedged somehow in between rocks, behind the skimmer, or in plants or aqua mats, which are a fake kind of plant for ponds. The males come up behind her while she is wedged.
The female will then give an abdominal press to get un-wedged and in the process she expresses her eggs. Once the eggs come into contact with the pond water, they become sticky and get stuck to the plants. While this is happening, the males produce gametes which come into contact with the eggs and fertilize them.
Sometimes the males will keep rushing the female even after she has laid all her eggs, and she can get hurt in the process. It can be a good idea to remove her from the koi pond for a bit after she is done laying eggs to avoid injury.
The eggs stay on the plants until they hatch, which usually takes about 36 hours but can take up to 72. When the baby koi, called fry, hatch, they go to the bottom of the pond. At this point the baby koi are basically just two eyes, a brain, and a yolk sack. After about a day at the bottom of the pond, the koi fry have a swim-up phase once most of their yolk sack is gone.
During this phase, they swim up and stay in the plant material where they are fairly well-protected from predators. Usually you do not need to feed the koi fry. The baby koi will eat rotifers and copepods and other small things in the pond water. If for some reason the koi did not spawn in a pond and the koi fry are in a tub, then there are a few ways you can feed them. The first is to boil some water and crack an egg into it.
You then scramble the egg on top of the water and it will create a milky film which you can squeeze out in cheese cloth and spread into the water for the fry to eat. You can also crumble up freeze-dried krill or flake koi fish food to feed them. You can also blend koi food and water in a blender and use that for the fry.
Sometimes, baby koi will eat each other. Once they can open their mouths wide enough to eat the smallest koi, they will. This can snowball in some cases, creating a koi cannibal that will try to eat all the other koi fry. There are certain species of koi that grow faster than others, which is important to consider when stocking your koi pond.
For example, gosanke grow slower than ogons, and often baby koi ogons will eat all the baby gosanke. If you do end up with a large cannibal koi, it is a good idea to remove it from the koi pond and place it with other large cannibals. They can be grouped in sizes like this to prevent further cannibalism.