Section 1: Preparation of Koi Breeding Facilities
I. Preparation of the Spawning Pond
Before breeding, it is best to keep female and male fish separately and reintroduce them into the spawning pond during the breeding period. Small concrete ponds are commonly used as spawning ponds, typically measuring 5 meters in length, 4 meters in width, and 0.8 meters in depth, with a water depth of 0.4–0.5 meters. A pond area of about 20 square meters is usually sufficient, with one pair of broodstock per square meter. Attention must be paid to pond disinfection and the pre-placement of spawning substrates (fish nests) in the pond.
II. Preparation of Spawning Substrates (Fish Nests)
Koi eggs are adhesive; fertilized eggs adhere to aquatic plants or other substrates for development. Therefore, before spawning, fish nests made of aquatic plants should be placed in the spawning pond or tank, allowing fertilized koi eggs to adhere to the plants and facilitating later hatching.
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Types of Fish NestsThere are many types of fish nests. The selection principles are:
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The fish nest should preferably float in the water and spread out over a large area to facilitate egg adhesion.
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The material should be soft to prevent injury to the fish during chasing.
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It should not easily decompose or adversely affect water quality, ensuring successful hatching.Common materials include hornwort, pondweed, water hyacinth, water lettuce, hydrilla, willow roots, and palm fiber.
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Treatment of Fish NestsAquatic plants used for fish nests are often collected from natural water bodies and may carry eggs of wild fish, predators, or pathogens. Therefore, they must be collected about half a month in advance, treated to remove dead leaves, cleaned thoroughly, disinfected, and rinsed with clean water to remove any residual chemicals before use.Common disinfection methods and chemicals include:
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Soaking in a 2% saline solution for 20–40 minutes to kill bacteria and parasites. This also helps detach hydra from the plants without harming them.
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Soaking in a 1×10⁻⁶ mg/L potassium permanganate solution for about 1 hour, followed by thorough rinsing.
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Soaking in a 20×10⁻⁶ mg/L nitrofurazone solution for about 1 hour, which has strong bactericidal properties.
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Soaking in an 8×10⁻⁶ mg/L copper sulfate solution for about 1 hour to kill hydra and bacteria.
For willow roots, palm bark, or palm fibers, disinfect them first, tie them into small bundles, and secure them with ropes in the spawning pond. -
Section 2: Preparation of Koi Broodstock
I. Sex Identification
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Body Shape: Females are shorter, thicker, and fuller, with a noticeably enlarged abdomen, especially as spawning approaches in mid-to-late April. Males are slender.
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Vent: The female vent is wide and slightly protruding. Light pressure on the abdomen releases eggs. The male vent is small and concave, with milt released upon gentle pressure.
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Pectoral Fins: Male pectoral fins are thick and stiff, with slightly smaller, rounded tips. Female pectoral fins are larger and more rounded. During sexual maturity, males develop “breeding tubercles” on the pectoral fin edges, giving them a rough texture when touched, while females remain smooth.
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Head: Females have a narrower, longer head. Males have a broader, shorter head with a slightly protruding forehead.
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Spawning Behavior: Females swim actively during spawning, enticing males to chase.
II. Selection of Broodstock
Breeding koi requires purposeful selection of broodstock. Since koi are primarily viewed from above, choose fish with a flat top-to-bottom profile, an elliptical cross-section, and a spindle-shaped body. Color selection depends on breeding goals. For example, to breed Kohaku, select healthy male and female Kohaku. Allowing different varieties to breed naturally in a large pond will not yield satisfactory results. Ideal broodstock should meet the following criteria:
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Pure lineage.
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Healthy, disease-free, and free of injuries or deformities. All fins should be intact.
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Vibrant, clear colors with sharp, distinct patterns and no fringing or blemishes.
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Smooth, well-aligned scales.
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Steady swimming posture.
For breeding, a ratio of one female to two males or two females to three males is recommended to ensure sufficient sperm and higher fertilization rates. Although one-year-old koi are sexually mature, males aged 3–5 years and females aged 4–10 years are ideal. Such broodstock are robust, have well-developed gonads, and produce high-quality eggs and sperm, resulting in excellent fertilization and hatching rates. Broodstock that are too old may have reduced hatching rates.
Section 3: Artificial Breeding of Koi
I. Artificial Insemination
During artificial insemination, hold the broodstock with one hand grasping the caudal peduncle and the other supporting the head and dorsal area. Position the fish at a 45-degree angle with the belly facing upward, gently dry the body surface, and apply light pressure to the female’s abdomen to release eggs into a dry, clean white basin. Simultaneously, squeeze milt from the male onto the eggs. Gently mix with a sterilized feather to facilitate fertilization. After 2–3 minutes, evenly distribute the fertilized eggs onto pre-placed fish nests in a shallow basin. Allow them to settle for 10–15 minutes until the eggs adhere firmly. Rinse with clean water to remove excess milt, then proceed to incubation.
II. Incubation
The incubation water depth is typically 40 cm. A 3 m × 3 m concrete pond is suitable, with water quality and temperature requirements identical to those during spawning.
Fertilized koi eggs absorb water and become adhesive, adhering to the fish nests for incubation. After spawning, remove the nests with attached eggs, disinfect them by soaking in a 5%–7% saline solution for 5 minutes, and then transfer the broodstock out. Incubation can take place in the spawning pond or a dedicated incubation pond. The incubation period depends directly on water temperature. Within the suitable range, higher temperatures shorten the period:
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At around 18°C: 4–5 days.
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At 20–22°C: 3–4 days.
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At 25°C: about 3 days.
III. Post-Spawning Broodstock Management
After spawning, promptly transfer the female and male broodstock to separate rearing ponds with aged water at the same temperature as the original pond. This is especially important for valuable varieties. Avoid mixing them post-spawning, as chasing during breeding can cause injuries to mucous membranes, skin, or scales. Broodstock are also weakened after spawning. When moving them out of the spawning pond or during cleaning and water changes, transfer them along with water to minimize stress. If injuries are observed, promptly apply antiseptic to wounds. Feeding should be careful and attentive, with close monitoring of activity and appetite. Start with small amounts of highly palatable feed and return to standard feeding and normal management once the fish recover fully.
