Squid breeding technique

First, the selection of broodstock mullet. There are two main ways to choose the fish for spawning. One is to collect them from specialized fry ponds where they are raised in controlled environments. The other is to select two-year-old sexually mature mullet from regular culture ponds, although this method is more labor-intensive. Female black mullet that are ready to spawn have a swollen and soft belly, with a clearly visible ovary outline and a reddish, prominent genital pore. Male mullet, on the other hand, display a striking purple coloration along their sides, with small white circular spots running vertically from the dorsal fin down the body. The more spots a male has, the more mature it is, and the redder its reproductive opening tends to be. Second, the use of hormones. From April to July, when the water temperature stabilizes above 20°C, hormone treatments can begin. The primary hormones used are LHRH analogs (LRH) and human chorionic gonadotropin (HCG). For female mullet, the recommended dose is 3–6 micrograms of LRH-A3 per kilogram or 800–1200 IU of HCG per kilogram. Males receive about two-thirds of the female dosage. During the early stages of hormone treatment (April–May), using both hormones together often yields better results than using just one. The exact dosage depends on the maturity level of the fish. Typically, 4–6 μg/kg of LRH-A3 or 600–800 IU/kg of HCG is used. As the water temperature rises during the middle and later stages of treatment, the dosage should be gradually reduced. The amount is calculated based on the total weight of the fish and then mixed with physiological saline or injection water. Each fish typically receives 1–3 ml of the solution, depending on its size. Hormone injections are now widely available and easy to administer. When administering the injections, the selected mullet are placed in a plastic basin. With one hand, the head is gently covered with a felt pad, while the other hand holds the syringe. The needle is inserted at a 45- to 60-degree angle, aiming toward the head, just below the pectoral fin. The needle should be pushed in about 0.8 to 1.5 cm. In the early stages of hormone treatment, two injections are usually given. The first dose is about one-third of the total, and the remaining portion is administered after 12–16 hours. Males are generally injected once, preferably during the second injection of the females. This helps ensure that the males are fully matured by the time spawning begins. Third, spawning. Mullet tend to compete for mates before spawning, which can interfere with the process. To improve fertilization rates, a small mesh cage is used as a spawning container instead of a large pond. These cages are made of polyethylene mesh, measuring 1 square meter in area with a height of 1–1.5 meters and a cover to prevent the fish from jumping out—mullets are known to leap over 1.5 meters. The cages are placed in a shallow pond, about 0.5–1 meter deep. After the second injection, the fish are placed into the cages, with one male and one female per cage. Some aquatic plants are also added to help the fish build nests. Spawning typically occurs 30 hours after the first injection when the water temperature is between 20–22°C. If the temperature is maintained at 23–25°C, spawning may occur within 17–20 hours. The eggs float in the nest and take about 12–15 hours to complete spawning. It’s important to keep the environment quiet, as any disturbance can stop the process. Spawning often happens in the middle of the night, when the fish are most active and least disturbed. Fourth, incubation. After spawning, small-scale operations may leave the fertilized eggs in the cage to hatch naturally. Alternatively, the eggs can be collected and transferred to a plastic basin for indoor incubation, with approximately 500–1000 eggs per liter of water. For large-scale production, the eggs are placed in hatching tanks or incubation systems with microfluidic water flow, with 60–100 million eggs per cubic meter. Fertilized eggs appear golden brown and gradually darken as the embryos develop, while unfertilized eggs turn yellow and eventually become white. The hatching time depends on the water temperature. At 22°C, hatching takes about 60 hours; at 25–26°C, it takes around 36 hours; and at 30°C, it takes about 30 hours. Once the fry emerge from the egg membrane, they rely on their yolk sac for nutrition. As the yolk is absorbed, the fry start swimming and begin feeding. This process usually takes 3–5 days, after which the fry can be moved to a rearing pond. During the incubation period, several management tasks are essential: (1) Still water hatching in basins requires changing the water twice daily, at least half of the volume each time, and careful handling to avoid damaging the eggs. (2) Maintaining a stable water temperature is crucial—temperature fluctuations should not exceed 2°C. (3) For cylindrical or barrel-shaped hatching systems, the filters must be cleaned regularly to prevent clogging. Cages should be washed every 1–2 days to ensure proper water exchange. (4) Unfertilized or moldy eggs should be removed promptly to prevent contamination.

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