How long does it take for koi fish eggs to hatch? Koi eggs take roughly a week to hatch, give or take a day or two accounting for temperature of the water. You do want to make sure that you remove the parents or eggs to a q…uiet tank or pool, the parents will eat the eggs and young fry. Other pond fishes such as loaches, catfish, plecos, and high fin sharks will also prey on the eggs and fry.