The eggs of koi fish have the following characteristics:
Appearance and Form
They are white or pale yellow, with a diameter of about 2.5 millimeters.
After the egg membrane absorbs water, the diameter can reach 1.4-1.8 millimeters.
The surface is sticky, allowing them to attach to aquatic plants or artificial spawning nests.
Developmental Characteristics
In the early stages of incubation, fertilized eggs will show structures such as eyes and vertebrae.
Unfertilized eggs tend to turn white, become transparent, or break, while fertilized eggs remain golden yellow and have strong toughness.
Observations in Artificial Breeding
Methylene blue solution can be used to distinguish fertilized eggs (which do not change color) from unfertilized ones (which turn blue).
During the hatching process, the eggs will gradually show embryonic features and hatch in about 4-5 days.
Newly hatched fry are only 2-3 millimeters long and need to be raised in separate tanks.
These characteristics apply to both natural reproduction and artificial hatching. The sticky nature of the eggs means that koi reproduction relies on aquatic plants or artificial spawning nests.