Hatchfish hatching technique

Fertilization Method (1) Select white-tailed pike with a maturity age of 2+ years, weighing between 700 and 1000 grams for broodstock. This ensures the fish are mature enough to produce high-quality eggs. (2) Dry insemination is commonly used in this process. After insemination, talcum powder is applied to reduce stickiness. When performing artificial insemination, the fish should first be wiped with a clean cloth. The female eggs are then gently squeezed into a dry basin, ensuring minimal contact with water to prevent premature swelling of the fertilized eggs, which can lower the fertilization success rate. Fertilization Process (1) During the first three days after fertilization, the eggs are in a critical phase where sperm-egg binding is unstable. Stirring or disturbing the eggs during this time should be avoided to maintain viability. (2) Maintain the pH level between 7.5 and 8. If the pH drops below 7.5, it can be adjusted using analytical-grade sodium bicarbonate. This helps create an optimal environment for successful fertilization. Incubation (1) The incubation density should be set between 150,000 to 300,000 eggs per square meter in the hatching frame. This prevents overcrowding and ensures proper water flow. (2) Hatching should occur in low-light conditions. The first two days are crucial, so light and vibrations must be minimized. As the embryos develop, the color of the eggs changes from yellow to yellowish green and finally to dark brown. Newly hatched fry have a sticky area on the back of their heads, allowing them to attach to the brown sheet or cage walls. (3) Temperature should be gradually increased during incubation, not exceeding 0.5°C per hour to avoid thermal shock. The ideal water temperature range is 8–12°C, with dissolved oxygen levels maintained between 7–9 mg/L. (4) Regular cleaning and inspection of the screens around the hatching box and outlet filters are essential to ensure smooth water circulation. (5) In the early stages of hatching, water flow should be reduced to prevent the eggs from being displaced. Strong currents can damage or kill the eggs, reducing hatch rates. Emergence (1) Immediately after the film (egg membrane) is released, the fry should be carefully removed. Be cautious not to let the fry sink to the bottom along with the egg membranes, as this can lead to suffocation. (2) The stocking density in the seedling pool should be adjusted according to the growth stage of the fry. Overcrowding can cause oxygen depletion and result in mass mortality. (3) The water in the seedling pool must be running water to maintain good water quality. Dissolved oxygen levels must meet specific standards. Oxygenation devices can be used to increase oxygen levels, but overuse may cause hypoxia or congestion in the fry, leading to high mortality. Seed Stocking (1) Select healthy white-spotted dogfish with strong vitality, good body condition, no signs of disease or injury, and uniform size. This ensures better survival and growth rates. (2) Before stocking, disinfect the fry by dipping them in a 3% to 5% saltwater solution for 3–5 minutes. This helps prevent diseases such as water mold and improves overall fry health.

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