(1) Broodstock Breeding. Broodstock should be raised in specially designed ponds, typically ranging from 1 to 2 mu in size with a depth of 1.5 to 2 meters. The water source should be clean, and the pond should have good drainage and irrigation systems. A muddy or sandy bottom with aquatic vegetation is ideal for supporting natural feeding behavior. Fish should be fed an appropriate amount of bait fish daily, and males and females should be kept in separate ponds approximately two months before breeding. In some lakes or reservoirs where squid populations are abundant, adult fish caught in spring can also serve as broodstock. Select individuals weighing over 0.5 kg for males and 1–3 kg for females, ensuring they are healthy and free from injuries.
(2) Sex Identification. Female fish have a rounded lower jaw that slightly protrudes beyond the upper jaw. Their genital opening appears as a "one"-shaped slit, surrounded by pink tissue, located between the anus and urinary pore. Males, on the other hand, have a pointed lower jaw that extends significantly beyond the upper jaw. Their genital and urinary openings merge into a single small hole behind the anus. When mature, the female’s abdomen becomes swollen, soft, and elastic, with visible ovarian contours and a slightly concave midline. Pressing the abdomen causes milky white milt to flow out from the male’s genital opening.
(3) Oxytocin Induction and Hatching. To induce spawning, a mixture of salmon pituitary (PG), human chorionic gonadotropin (HCG), and luteinizing hormone-releasing hormone analog (LRH-A) is commonly used. The dosage is typically 5.2 mg PG per 1,000 units of HCG or 10 mg PG with 300 micrograms of LRH-A. Injection is usually administered at the base of the pectoral fin, either once, twice, or three times. The effect lasts about 6–12 hours, longer than in most fish species. Fertilization methods vary depending on production scale and broodstock availability. Natural spawning is preferred for large-scale operations due to less stress on the fish, while artificial insemination is more suitable for smaller-scale breeding. Combining both methods is also possible—after natural spawning, broodstock that did not release eggs can be manually inseminated. Squid-like fish have sharp, hard rays, so when handling them, grasp the mandible with your thumb and forefinger and lift the fish. Wrap it in gauze or a towel to protect both the fish and the handler. Fertilized eggs hatch directly in circular tanks. Due to their slight viscosity and semi-floating nature, they tend to sink in still water. Therefore, maintaining a water flow of at least 20 cm/s is essential to prevent sinking and ensure high hatching rates. If no circular tank is available, running water hatching tanks can be used instead. Water quality must be carefully controlled—fresh, well-oxygenated, and pollution-free. Maintain a temperature of 23–29°C for optimal development. The embryonic development of these eggs is slower compared to domestic fish, taking around 30 hours to hatch at 25–30°C.
(4) Seed Cultivation. The cultivation of carp fry can take place in seedling ponds or cages, but requires careful management. Seed ponds are typically 0.1–0.2 mu in size with a depth of 1.5 meters, clean water, and a silt-free bottom. For easier handling, many farms now use hatchery rings or cages placed within the pond. Cages are set in areas with gentle water flow, and both the cage and fish are sterilized before stocking. The period from hatching to the development of fins is called the "opening phase," lasting about 3 days. During this time, live feed such as 24–72-hour-old rainbow trout fry or 24–60-hour-old grass carp fry is introduced. Carp larvae usually begin feeding 1–2 days after oxytocin treatment. The density of live feed should be 15 times that of the carp fry to encourage feeding. From the opening stage to reaching 3.3 cm in length, which takes about 12–18 days, the fry can be sold or transferred to adult ponds. Ensuring a steady supply of nutritious live feed and regular disinfection and disease prevention are crucial for survival. Common diseases at this stage include saprolegniosis, nematodes, and small melon worms, which thrive in temperatures between 20–30°C and can cause significant losses. To prevent these, live feed should be soaked in 3% saltwater for 10–20 minutes. Carp fry can be treated with formalin solution at 150–200 g/m³ for 1–2 minutes. For treatment, a mixture of copper sulfate and ferrous sulfate (5:2) at 0.7 g/m³ can be applied 2–3 times daily, followed by a 2% formalin dip. For small echinococcosis, a 2 g/m³ mercuric nitrate dip for 3–5 minutes or 0.1 g/m³ Quanchipid is effective. Rickets disease can be treated with 0.2–0.5 g/m³ trichlorfon or 1.5 g/m³ potassium permanganate bath for 5–10 minutes. Once the fry reach 3.3 cm, disease incidence decreases, and they begin to resemble adult fish with improved feeding abilities. Eel fry require different types of live feed at each growth stage. If not provided timely, they may cannibalize or starve. Therefore, it's important to plan and supply various sizes of live feed according to the fry’s growth rate. If further rearing is needed, fry can be kept in cages, cement pools, or small earthen ponds. Stocking density in flowing water is 200–500 fish per cubic meter, while static water requires 100 fish per cubic meter. Live fish fry or wild shrimp and fish are commonly used as bait.
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