Japanese Koi Artificial Propagation Technology

Broodstock Selection The selected fish should exhibit clear and distinct characteristics, such as a strong physique, vibrant body color, cloud-like patterns, pure and spot-free features, and stable genetic traits. The broodstock should be at least 3 years old, with carp weighing over 2.5 kg for males and 2 kg for females. A sex ratio of 1:1 is acceptable, but 1:2 (one male to two females) is preferred to enhance breeding success. Intensive Broodstock Cultivation Broodstock should be raised in cement pools measuring 100 m² with a water depth of 1.2 meters. Each pond can hold 4 to 8 fish. Water quality is crucial—dissolved oxygen levels must be maintained at 5 mg/L or higher, and the temperature should range between 18°C and 22°C. Feed squid buoyant bait, with an amount equal to 2% of the broodstock’s weight per day, given once in the afternoon. Incubation and Hatching (1) Preparation of Spawning Pools Ten cement pools measuring 4m x 1.5m x 0.8m are used. These are covered with shade nets and plastic film to protect from acid rain and glare. A small water tower provides filtered, oxygenated water, with three air stones per tank. Water depth is kept at 0.6 meters, and the temperature is maintained between 22°C and 24°C. A 3.4m x 1.2m x 0.8m cage is placed inside each pool, with four bamboo structures above, spaced 25 cm apart, each containing a sterilized brown-fish nest. (2) Pre-Oxygenation Evaluation At 21°C, gonadal development is assessed. If not fully developed, LRH-A2 is administered at 0.3 μg/kg via injection into the back muscle. Fully developed gonads do not require additional stimulation. After 8–10 days, if the female's abdomen swells, the gonads are soft, and the vent appears reddish with some eggs released upon gentle pressure, it indicates readiness for spawning. (3) Oxytocin Administration LRH-A2 is injected at 1.5 μg/kg into the base of the pectoral fin. After injection, the fish are placed in the spawning pool. Each pool contains one female and one or two males. Continuous microflow water and oxygenation stimulate spawning, which typically lasts 21–43 hours. (4) Spawning and Fertilization Spawning usually occurs around 4 AM, when fish aggressively chase each other near the nests. After about 30 minutes, eggs are laid and fertilized. Eggs adhere to the nests. At dawn, broodstock are returned to their rearing pools for recovery, and some may spawn again later. Each spawning yields 100,000 to 300,000 eggs, with a fertilization rate of 80–90%. (5) Hatching Egg development is monitored. If many eggs are fertilized, they are moved to separate pools, with 50,000 to 100,000 eggs per pool. Methylene blue at 1 ppm is added to prevent fungal infections. At 22–24°C, hatching takes 76–92 hours, with hatching time inversely related to temperature. (6) Fry Holding Newly hatched fry have limited swimming ability and often cling to cages or nests. After 2–3 days, the yolk sac disappears, and the digestive system begins to develop. At this stage, feed them algae, 150-mesh sieved egg yolk, or soy milk. After 3–5 days, fry become more active, and the yolk sac is fully absorbed. They are then transferred to ponds for further growth. Breeding and Seed Cultivation Seed cultivation follows similar practices to common carp. Ponds ranging from 400 to 800 m² are used, with a depth of 1.2 meters. Sludge levels should be controlled, and each pond has 1–2 aerators. Ten days before stocking, lime is applied at 50 kg/mu, followed by 400–500 kg/mu of fermented pig manure. Water is filled to 50 cm to promote algal growth. Green algae, rotifers, and other microorganisms thrive, providing food for the fry. Each acre can support 150,000 fry, with 2 kg of soy milk fed daily, divided into two meals. As fry grow, water levels increase, and feed amounts are gradually adjusted. By day 20, fry reach 3 cm in length and are ready for sale or grading. Fry Screening Large and tri-colored koi, particularly red-and-white varieties, reach 8–10 cm in length after 60 days. At this stage, their color becomes distinct, and basic patterns are established. Before screening, fish are exercised with net pulls to acclimate. Selected fry must have clear traits, robust bodies, bright colors, and cloud-like spots. Those with deformities, dull color, poor growth, or irregular patterns are discarded.

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