During spawning, female Koi fish sometimes experience dystocia or egg binding. Egg binding occurs when the female produces eggs, but the ovaries are not developed enough to release them. This leads to a build-up of eggs in the ovaries, which results in egg binding or impaction. Egg binding causes females to bloat. Spawning requires the males to forcefully bump into the female's sides to release the eggs. An egg bound female may be too weak to withstand the onslaught. Continued unchecked, the condition will lead to death.
Withhold food from the female koi once spawning is complete. As winter approaches, she will absorb the eggs back into her system as food. If she does not absorb the eggs, her abdomen will begin to harden.
Increase the temperature to 25 degrees Celsius for seven days. Koi traditionally spawn when the water temperature increases to 20 degrees Celsius in late summer. The increase in temperature can assist in preparing her ovaries and you will be able to gently squeeze her sides to release the eggs. You should squeeze very gently to avoid injuring the koi. If gentle pressure does not yield eggs, you will have to try injections.
Obtain CPE (carp pituitary extract) from your local veterinarian. The powdered extract is harvested from the pituitary gland of the carp. You will have to mix it with sterile water or saline solution according to the manufacturer's instructions. Inject 0.3g per kilogram of body weight. After 18 hours, administer another injection. After 10 hours, you can attempt to manually harvest the eggs.
Luteinizing release hormone or Human Chorionic Gonadotropin can also be used to induce spawning.