How many babies can a koi fish have at a time?

A koi fish can lay anywhere from 10,000 to 1,000,000 eggs at a time, depending on the size and age of the fish. Typically, a female koi will release her eggs in a spawning event, and the males will fertilize them. However, not all eggs will survive to hatch, as many factors can affect their viability, including predation and water conditions.