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Macrobrachium prawn breeding
First, the selection and transportation of broodstock.
Broodstock for shrimp farming is typically sourced from shrimp ponds and collected during mid to late October. When selecting broodstock, it's important to ensure they meet specific criteria: first, they should be large in size with uniform specifications. Female shrimp should generally be over 10 cm long and weigh between 25-30 grams. Second, they must be healthy, free from disease, have bright coloration, active movement, and fully developed appendages. Selection should be done carefully, ideally in water to minimize stress. Third, a balanced sex ratio is essential for optimal fertilization rates, usually maintained at a 3:1 male-to-female ratio. The number of broodstock reserved depends on individual size, planned nursery production, expected survival rate during wintering, and the maturity of nursery techniques. As a general rule, about 35 grams of female shrimp can produce around 2,000 eggs, assuming an 80% survival rate during winter.
Common methods for transporting broodstock include open canvas bags, canvas boxes, tin boxes, and nylon oxygenated bags. Canvas boxes are commonly used, measuring 0.8m x 0.8m x 1.0m, with transport time limited to less than five hours if water temperature is between 20-23°C. Each box can carry 20-30 kg of shrimp, and continuous aeration or oxygenation is necessary. Tin boxes, measuring 0.8m x 0.8m x 1.2m, are also used, with small shrimp boxes (about 60cm x 70cm x 12cm) placed inside. Up to 10 shrimp boxes can fit into one tin box, each holding 5-8 kg of shrimp. Oxygenation is required throughout the journey. Nylon oxygenated bags are suitable for small quantities, with each bag containing 8 liters of water and carrying 1.5-2.0 kg of shrimp. For larger volumes, live water trucks are recommended for better efficiency and conditions.
Second, the cultivation and management of broodstock.
This includes wintering management and pre-breeding strengthening. Broodstock are usually kept in fresh water during winter, using greenhouses, plastic film shelters, or deep well water for insulation. The wintering pond area is typically 50-100 square meters. Before introducing broodstock, the pond must be disinfected with bleaching powder (15g/m³) or potassium permanganate (100g/m³). Stocking density is controlled at around 15-20 tails per square meter. The wintering period usually lasts from November to April. Pre-breeding strengthening begins at the end of February and early March, with the following management practices:
1. Water temperature control: In early winter, the temperature should be maintained at 20-23°C. During the pre-breeding phase, it should gradually increase to 25-26°C, with daily fluctuations kept within 3°C. Shade structures should be installed above the pond to prevent direct sunlight.
2. Feeding: During early winter, feed can include fish meat, shellfish, bean cake, cooked barley, and corn, as well as pellets. Daily feeding is about 4% of the shrimp’s body weight, with dry feed at 1-2%. Feeding occurs twice daily, with 70% of the food given at night. In late winter, when intensive culture begins, animal feed increases, and daily feeding reaches 5-7% of body weight. Residual feed should be removed before each feeding, and feed type and quantity adjusted based on weather and intake.
3. Water quality management: Aeration systems are essential, with one air stone per 2-4 square meters in a 50-square-meter pond. Continuous aeration at night ensures dissolved oxygen remains above 3 mg/l. Waste should be removed daily, and water changed regularly—every 5-7 days, replacing 1/3 to 1/2 of the water. During intensive culture, more frequent changes are needed, but temperature differences must not exceed 1°C. Preheated water at 20-23°C or 25-26°C is ideal.
4. Disease prevention: Broodstock should be disinfected before entering the pond. Antibiotics like oxytetracycline (1g/m³) or chloramphenicol (0.5g/m³) are used every 15 days to prevent infections.
Third, broodstock spawning and hatching.
Macrobrachium rosenbergii broodstock begin spawning after about two weeks of incubation at 25-26°C. At this stage, broodstock should be moved to spawning pools. To facilitate larval rearing, some broodstock can be transferred to a separate larval tank for egg incubation. During this period, maintaining stable conditions for both broodstock and eggs is crucial.
1. Water temperature and salinity regulation: Fertilized eggs hatch best at 26-28°C. Temperature stability is essential, and water exchanges must be carefully managed. Freshwater is used initially, and once eggs turn gray (around day 12), a small amount of seawater is added daily to raise salinity to 0.12-0.14%. This helps larvae adapt to saltwater before hatching.
2. Feeding and water quality: Egg-bearing shrimp continue to feed during hatching, consuming fresh fish, snail meat, and other nutritious foods. Waste is removed regularly, and aeration is maintained to keep oxygen levels near saturation.
Fourth, larval rearing.
After hatching, broodstock are moved to a separate pool, and zoea larvae are raised in specialized tanks.
1. Pond requirements: Cement pools with aeration pumps, pipelines, drainage systems, and backup generators are standard. Plastic tanks or barrels may also be used for hatching.
2. Seawater source and preparation: Juvenile larvae require a salinity of 0.012-0.014%. Coastal areas can use natural seawater mixed with freshwater, while inland areas can prepare artificial seawater.
3. Larval density: A typical density is 5-10 million larvae per cubic meter. Different stages should not be mixed, and each cubic meter can support 2-40 thousand seedlings.
4. Feeding: Newly hatched larvae feed on yolk sacs, then transition to plankton, algae, yeast, and rotifers. After molting 4-5 times, they can be fed minced fish and egg yolks three times daily. Regular cleaning and water changes are essential to maintain water quality.
5. Salinity adjustment: After metamorphosis, larvae must acclimate to freshwater by gradually reducing salinity. This process takes about one day, after which they are ready for stocking or sale.