Koi eggs hatch about three days after females lay them; in colder temperatures, the time can be as long as four days. They are laid in clutches that average 30,000 eggs, after which they are fertilized externally by the males.
Female koi, a domesticated, colorful type of the common carp, spread their eggs energetically on aquatic plants as they are laid. They provide no further parental care to the eggs. Newly hatched koi feed on microscopic plankton including rotifers, copepods and algae. After about a year, they begin to eat small invertebrates such as caddis flies, mollusks and crustaceans. Adult carp eat a wide variety of animal species along with plant tubers and seeds.