Squid breeding technique

First, the selection of mullet for breeding

When it comes to choosing mullet for breeding, there are two main options. The first is to select fish that have been raised in special ponds, where they are carefully monitored and nurtured. The second option involves selecting two-year-old sexually mature mullet from a culture pond, though this process is more labor-intensive. For female black mullets, signs of sexual maturity include a swollen and soft belly, with a clearly visible ovary and a reddish, prominent genital opening. Male mullets, on the other hand, display a striking purple coloration along their sides, with small white spots arranged vertically from the dorsal fin downward. The more spots a male has, the more sexually mature it is, and the redder its genital pore appears.

Second, the use of oxytocin

Oxytocin is typically administered from April to July when the water temperature stabilizes above 20°C. Commonly used hormones include luteinizing hormone-releasing hormone (LRH) analogs such as LRH-A3, and human chorionic gonadotropin (HCG). For female mullet, the recommended dosage is 3–6 micrograms of LRH-A3 per kilogram or 800–1200 International Units of HCG. Males are usually given two-thirds of the female dose. During the early stages of the process (April–May), using both hormones together tends to yield 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 for females. As the water temperature rises during the middle and later stages, the dosage should be gradually reduced. The amount is calculated based on the number of fish and their total weight, then diluted in physiological saline or injection water. Each fish receives approximately 1–3 ml, depending on its size. Hormones are now widely available for this purpose.

During the injection process, the selected mullet are placed in a plastic basin. With one hand covering the fish's head, the other hand holds the needle at a 45–60 degree angle, inserting it into the body near the base of the pectoral fin. The needle should be inserted about 0.8–1.5 cm deep. In the early stages of the process, two injections are usually required. The first dose is about one-third of the total, and the remaining portion is injected after 12–16 hours. Males are typically injected once, preferably during the second injection of the female. This helps ensure proper maturation and successful spawning.

Third, spawning

Mullet often compete for mates before spawning, which can interfere with the process. To improve fertilization rates, small mesh cages are used as spawning pools instead of large ones. 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—since they can leap over 1.5 meters high. The cages are placed in shallow water, 0.5–1 meter below the surface. After the second injection, one male and one female are placed in each cage. Some aquatic plants are added to help the fish build nests and spawn. Spawning time varies with water temperature: at 20–22°C, it takes about 30 hours, while at 23–25°C, it occurs within 17–20 hours. Eggs are released in clusters and float in the nest, with spawning lasting 12–15 hours. It's important to keep the environment quiet, as disturbances can halt the process entirely. Spawning typically occurs during the quietest hours of the night.

Fourth, incubation

After spawning, small-scale breeders may choose to let the eggs hatch inside the cage, or they can collect the eggs and transfer them to a plastic basin for indoor incubation. In this case, the eggs are placed in 500–1000 per liter of water. For larger-scale operations, fertilized eggs can be placed in hatching tanks or microfluidic incubation systems, with 60–100 million eggs per cubic meter of water. Fertilized eggs appear golden brown and gradually darken as the embryos develop, while unfertilized eggs turn yellow and eventually become white. The incubation period 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 only takes 30 hours. Once the fry emerge, they rely on their yolk sac for nutrition. As the yolk sac is absorbed, the fry begin to swim and start feeding. This development stage lasts about 3–5 days, after which the fry can be transferred to a nursery pool. Throughout the incubation phase, several management tasks are essential. These include maintaining still water conditions, ensuring stable temperatures, regularly cleaning hatching containers, and removing any unfertilized or moldy eggs promptly.

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