Some fish can become pregnant and are live-bearers. Koi do not fit into this category. A female Koi will lay eggs. The eggs must be pushed out of her by the male. There are signs to look for to determine if your Koi is full of eggs.
1. The Koi looks fat or bloated.
2. The males are chasing the female around the pond. It can be quite aggressive as they may bash her against the side of the pond.
3. Koi is swimming far from the surface, rarely coming up.
4. The female stays away from the other fish because she is looking for a place to lay eggs.
5. The female Koi may suck on plants or the sides of the pond to clean space for the eggs.
6. The male gains white spots on their pectoral fins and the covering of their gills.
7. A month before they begin to spawn they begin eating at an optimum level.
Most often your male Koi will be 3-5 and the female 3-6 years old before they are mature enough to spawn. Your Koi will become interested in Spawning (mating) in the spring and most experts say it is usually after the first water change. The water will be 65-70 degrees during spawning. Once the males bash against the female the eggs will be released and the males will fertilize the eggs at that time. The eggs are very sticky and will stick to most anything. The Koi love to eat the eggs as they are released. It is a tasty treat to them.
You must watch closely to catch the spawning process. If you want to save any eggs you’ll need to place ropes (even a mop will work) into the pond for the eggs to attach to. Very soon after they are attached you must move then to another tank/pond. The Koi usually spawn early in the morning. If you suspect it is about time check your pond frequently as the fish may jump out of the water. If you find them soon enough you can return them to the pond and they will live. A sure sign that they have already released the eggs is bubbles or foam on the water along with a bad smell. Also the ammonia levels will soar.
If you pay close attention to your Koi on a daily basis you will recognize the signs. Getting to know your Koi is the key to determine if they are ready to spawn. I’ve been told that spawning happens most often when there is a full moon. The same has been said about babies. You decide if it is true. When were your Koi’s eggs laid?