How to Keep Koi? Fry Selection and Adult Fish Rearing and Management Methods

I. Fry Selection After hatching, the fry are reared for 20 to 30 days. When the fish body grows to about 3 cm, selection begins, culling the inferior and keeping the superior, strengthening the growth rate, so as to protect the traits. Selecting fry is the most important step in obtaining high-quality koi during the rearing process. Generally, 3 to 4 selections are carried out over a period of more than 3 months after hatching. The 1st selection is carried out within 20 to 30 days after the fry hatch, when the fry body length reaches about 3 cm. It mainly selects and keeps individuals with a strong constitution, lively swimming, a straight spine, no deformities or defects in the fins, and obvious breed characteristics. Other individuals are culled or separately raised for sale, but different breeds have different growth rates and times for forming markings, so the time for breed characteristics to appear also varies. For example: Showa Sanshoku koi begin to show them about 15 days after hatching, while Ogon koi show them about 50 days after hatching. The 2nd selection begins about 20 days after the 1st selection, with selection standards being whether the shape of each fin is graceful, especially the pectoral fins, whether the head shape is symmetrical, whether the eyes, snout, and barbels are deformed, whether the colors are bright and deep, whether the pattern markings are clear, and whether the breed characteristics are obvious. The 3rd selection is about 20 days after the 2nd selection.

Selection standards: the size proportion of the fins must be appropriate, the colors bright, the white base pure with no stains, red patches with clear edges, black patches even in shade, markings balanced left and right, and if there are white parts on the snout and caudal peduncle they must be clear, with obvious breed characteristics, etc. The 4th selection is basically the same as the 3rd. After the above 3 to 4 selections, generally among the offspring bred by each fish, only 1000 to 3000 or fewer finally meet the requirements. Koi are large fish and have food value; the fry culled through multiple selections can be raised as food fish. II. Rearing and Management of Adult Fish Koi have a relatively large food intake, and a sparser stocking density is better. For large-scale cement pond culture, 3 to 5 fish per sq m is appropriate, with proper mixed culture with grass carp, silver carp, bighead carp, etc. Koi are omnivorous fish, and leftover rice, leftovers, fruit peels, etc. can be mixed with about 10% animal-based feed such as animal offal, golden apple snails, maggots and pupae, and earthworms to make pellets for feeding. Their feed protein content should reach about 35% and fat 5% to 8%. Feeding should adhere to the “four fixeds”; when feeding specifically, the amount should be appropriate according to fish size, climate change, and water quality conditions, with each feeding taking 15 to 30 minutes, and the daily feed amount being 5% to 6% of the fish body weight. In summer, feed once each at 6 am to 7 am and 15 pm to 16 pm, and in winter feed once at 13 pm to 14 pm. Persist in daily inspections, promptly remove leftover bait and residue, change the water once every 2 to 3 days in summer and once every 4 to 5 days in spring and autumn, with the water change volume being 1/3 to 1/2 of the original pond. Keep the water quality fresh. In high-temperature rainy weather, pay attention to aeration to prevent pond turnover. In winter, koi can be moved indoors, with the indoor water temperature kept at 2 to 10°C, and easily digestible bait appropriately fed to ensure safe overwintering.