When it comes to fish having babies, there are two main ways that the females give birth. There are the fish that give live birth and there are the fish that lay eggs on some kind of surface such as branches. Koi fish are part of the group of fish that lay eggs. When you own koi fish, it is almost harder for them not to get pregnant. That’s how common it is.
For the individual koi fish owner, if you have male and female koi fish in your pond there is a chance they could spawn babies. Really, the female’s eggs will attach it itself to almost any surface. For large commercial operations as well as enthusiasts who breed for fun, there are certain products made to help you out with the job. There are certain grasses, water hyacinths, special mops and other devices that can be purchased at specialty shops and online.
Koi fish are usually ready to have babies by the time they are three or four years old. For the female fish to be able to have fish, you should feed her higher amounts of protein before she mates with the male. She could probably get pregnant regardless of her diet, but it’s beneficial to help the process along.
If this is a planned event, it makes sense to keep the male and female fish apart from each other to avoid having to clean up a big mess. Also, it becomes quite difficult to change the water after the female fish has given birth. If you do have a separate tank for mating, place the female fish in first in the morning and then the male fish a few hours later. This will let you keep track of what’s going on. The male fish push the female fish into whatever she is using to lay her eggs and then releases them. And that is how koi fish lay eggs.
After the eggs are laid, it is best to remove both koi fish from the separate mating tank (if you have one). Once the fish are laid, adult fish are very apt to eat the eggs. You will most likely want to do a water change with the water from the separate tank.
The eggs will need careful care for a few weeks. The water temperature should be no lower than 59 degrees, the water quality should be as perfect as you can get it and within a few days the new fish can start to eat live food such as brine shrimp. Within a few weeks they will be eating fish pellets and will be on their way to becoming a regular koi fish.