Japanese Koi Artificial Propagation Technology

Broodstock Selection The selected fish should exhibit clear and distinct characteristics, such as a strong and healthy physique, vibrant body color, cloud-like patterns, and pure, spot-free skin. They must have stable genetic traits and well-developed gonads, making them suitable for breeding. The broodstock should be at least three years old, with common carp weighing 2.5 kg or more and crucian carp weighing 2 kg or more. A sex ratio of 1:1 is ideal, although a 1:2 ratio (one female to two males) is preferred to enhance breeding success. Intensive Broodstock Cultivation Broodstock should be raised in controlled environments, typically in cement pools with a water depth of 1.2 meters and an area of 100 square meters. Each pool can hold 4 to 8 individuals. Water quality is crucial, requiring dissolved oxygen levels of at least 5 mg/L and a temperature range of 18°C to 22°C. Feeding involves squid-based floating bait, with the daily feed amount calculated as 2% of the broodstock's body weight. Feeding should occur once in the afternoon to ensure optimal nutrient absorption and growth. Incubation and Hatching (1) Preparation of the hatching pond includes setting up 10 cement pools measuring 4m x 1.5m x 0.8m. These pools are covered with shade nets and plastic film to protect against acid rain and glare. A small water tower is used to provide filtered, oxygenated water, with three air stones per tank. Water depth is maintained at 0.6 meters, and the temperature is kept between 22°C and 24°C. A 3.4m x 1.2m x 0.8m cage is placed inside each pool, with sterilized brown-fish nests spaced every 25 cm on bamboo frames above the pool. (2) Pre-oxygenation examination begins at 21°C, where the development of the gonads is assessed. If gonads are not fully developed, LRH-A2 (0.3 μg/kg) is administered via injection into the back muscles. Fish with well-developed gonads do not require additional treatment. After 8–10 days, if the abdomen swells, the gonads become soft and red, indicating readiness for spawning. At this point, the fish are moved to the oxytocin pool for further stimulation. (3) Oxytocin administration involves injecting LRH-A2 at a dose of 1.5 μg/kg into the base of the pectoral fins. Each pool contains one female and one male or one female and two males. Continuous microflow water and aeration stimulate spawning, which typically lasts 21–43 hours. (4) Spawning and fertilization usually occur around 4 AM, when fish actively chase each other near the nests. After about 30 minutes, eggs are laid and fertilized. The eggs adhere to the nest cages. Broodstock are returned to their rearing pools for recovery, and some may spawn again. Each batch produces 100,000 to 300,000 eggs, with a fertilization rate of 80–90%. (5) Hatching occurs within 76–92 hours at 22°C–24°C. The hatching time decreases as water temperature increases. Once hatched, the fry are carefully monitored and transferred to new pools to prevent overcrowding. (6) Fry Holding Newly hatched fry have limited swimming ability and often cling to cages and nests. After 2–3 days, the yolk sac disappears, and the fry begin to develop their digestive systems. At this stage, they can be fed with algae, finely sieved egg yolk, and soy milk. After 3–5 days of feeding in the cage, the yolk sac is completely absorbed, and the fry become more active. At this point, they are ready to be moved to larger ponds. Breeding and Seed Cultivation Seed cultivation follows similar practices to those used for common carp. Ponds ranging from 400 to 800 square meters are used, with a depth of 1.2 meters. Before stocking, the ponds are disinfected with quicklime and enriched with fermented pig manure. Water is filled to 50 cm to promote algal growth. A dense population of rotifers and copepods ensures adequate food for the fry. Each acre can support 150,000 fry, with daily feeding of 2 kg of soybean milk divided into two portions. As the fry grow, water levels are gradually increased, and supplementary feed such as carp bait is introduced. After about 20 days, the fry reach 3 cm in length and can be sold or graded. Fry Screening At 60 days of age, red-and-white koi reach 8–10 cm in length, with clear and stable color patterns. This is the ideal time for grading. Before screening, fish are acclimated with 2–3 net exercises. The selection criteria include retaining fish with strong, healthy bodies, bright colors, clear patterns, and no deformities or spots. Individuals with dull color, poor growth, or irregular patterns are culled to maintain quality.

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