Practical Tips for Selecting Young Fry When Keeping Koi

After hatching, koi fry are raised for about 20 days to 1 month, and when the fish body reaches about 3 cm, selection must be carried out. The purpose of selection is to remove the inferior and keep the superior, strengthen the growth rate, and thereby protect the genetic traits. Therefore, selecting young fry is the most important step in obtaining high-quality koi during the rearing process. Generally, selection work is carried out 3 to 4 times over a period of more than 3 months after hatching. The timing of selection varies depending on the variety, the speed of growth, and how early the markings appear.

For example, Showa Sanshoku koi can be selected when they have been hatched for more than two weeks; Ogon-system koi can begin selection at 50 days; and Kohaku and Taisho Sanshoku-system koi can only begin selection at around 60 days. In short, young fry must grow to a body length of 3 to 5 cm before selection can begin. The key points of selection are: first, remove fish that are deformed or have dull colors. Selection should also be carried out according to the standards of pattern growth and quality. For example, for Kohaku koi, those with pale red markings should be culled; for Ogon-system koi, those with a dull head, poor scale coverage, many miscellaneous spots on the body, or poor pectoral fin growth should all be culled.

During the rearing process, koi have a relatively high culling rate. If 1 brood fish generally lays 200,000 to 400,000 eggs, after hatching and several rounds of selection, only about 5,000 large fish can ultimately be kept. According to relevant data, when a brood fish lays 100,000 eggs, after 4 to 5 days of hatching, 60,000 to 70,000 fry are obtained; after another 20 days of rearing, 30,000 young fish with a body length of 2 cm can be obtained; by July, after the 1st selection, keeping the strong and removing the weak, only 16,000 are left; after the 2nd selection or culling during daily rearing, only 5,470 fish can be left; by November when overwintering begins, there are only 3,600 fish; at 1 full year, only 2,300 strong, large fish can be kept. This shows how high the culling rate is; it can truly be called “one in ten thousand.”