Key Points for the Fry and Fingerling Rearing Techniques of Koi
What are the key points for rearing koi fry and fingerlings?
When koi larvae are 3 to 4 days old after hatching, the yolk sac has been fully absorbed and they begin exogenous nutrition. If natural food is insufficient, feed cooked egg yolk liquid or rotifers, and improve water quality conditions. After 7 to 8 days, switch to slightly larger food, such as cladocerans, minced fish or pellet feed. After 20 to 30 days of rearing, when the larvae reach 3 cm in body length, selection (screening) must be carried out, removing the inferior and keeping the superior, to maintain the excellent traits of the breed. Selection is carried out 3 to 4 times within 3 months after hatching. Selection differs slightly depending on the variety, due to differences in growth rate and the time when the markings appear. For example, Showa Sanshoku koi begin selection at a little over 2 weeks after hatching, Ogon system koi begin selection at 50 days, and Kohaku and Taisho Sanshoku system koi begin selection at around 60 days. During selection, first remove fish that are deformed or not brightly colored, and then select according to the growth condition of the patterns and quality standards. For Kohaku koi, individuals with pale red markings should be culled. For Ogon koi, individuals with dull heads, poor scale coverage, many miscellaneous spots on the body, or poorly developed pectoral fins should all be culled. Koi have a very high culling rate during the rearing process. For example, if the parent fish spawn 100,000 eggs, 60,000 to 70,000 fry are obtained, and when reared to summer fingerlings there are still 30,000; after the first selection 16,000 remain, and by the time of autumn overwintering, only about 3 600 remain.
After the first selection, the remaining young fish can be placed in a pond of 5 m x 5 m, with a water depth of 30 to 50 cm, and a density of 120 to 150 fish per m. After the second selection, the remaining fish are stocked at a density of 90 to 120 fish per m. Thereafter they are gradually thinned out. When the fish reach 10 to 20 cm in body length, the stocking density should be comprehensively considered according to factors such as water body size, water quality conditions, equipment conditions and rearing techniques. After selection, koi can be fed soybean cake, rapeseed cake, pellet feed, or feed such as tubificid worms, mollusks and duckweed. The feeding rate is 10% to 30% of the fish body weight. And the water must be changed and dirt cleaned frequently.
After the first selection, the remaining young fish can be placed in a pond of 5 m x 5 m, with a water depth of 30 to 50 cm, and a density of 120 to 150 fish per m. After the second selection, the remaining fish are stocked at a density of 90 to 120 fish per m. Thereafter they are gradually thinned out. When the fish reach 10 to 20 cm in body length, the stocking density should be comprehensively considered according to factors such as water body size, water quality conditions, equipment conditions and rearing techniques. After selection, koi can be fed soybean cake, rapeseed cake, pellet feed, or feed such as tubificid worms, mollusks and duckweed. The feeding rate is 10% to 30% of the fish body weight. And the water must be changed and dirt cleaned frequently.