Broiler Selection and Feeding
The majority of broodstock used for seed production of Penaeus monodon in Guangdong is imported from countries such as Malaysia, Indonesia, and Thailand. These broodstock are transported over long distances and arrive at the shrimp farm in boxes. Upon arrival, they should be quickly moved to a holding tank. The process involves opening the box, separating males and females into fresh seawater contained in large basins, removing any dead shrimp, and counting the live ones. Healthy broodstock with fast-growing oyster shells are then placed into rearing ponds, while diseased or weak individuals are excluded.
After 1-2 days of recovery, the broodstock can undergo eyestalk ablation and maturation. This procedure should be carried out near the maturation tanks. After surgery, the broodstock are immediately transferred to the prepared maturation pools. The maturation process includes:
(1) Preparation of Maturation Pools
Maturation pools are typically built using cement tanks in dark rooms or conventional nursery rooms with black-painted walls or covered with black cloth to create a quiet, dark environment. The pools are filled with standard seawater to about 40 cm depth, heated to 28.5°C using titanium heating rods, and kept at a constant temperature until the broodstock are ready to enter.
(2) Feeding
High-quality fresh feed is provided four times daily—morning, afternoon, and during the night. Before each feeding, leftover food is removed. All operations are done by one person to ensure consistency and minimize stress. Live feeds include crabs, sandworms, small shellfish, cuttlefish, and squid, which are washed and cut into small pieces for easier ingestion. The maturation period starts after three days, and water changes should not exceed half the volume. Water temperature must match that of the maturation pool.
Typically, broodstock reach gonad maturity within 3-5 days. At this point, monitoring becomes crucial. A special lamp from Taiwan helps identify mature individuals. Once mature, they should be promptly moved to spawning tanks.
Local broodstock can be captured using specialized fishing gear. Captured individuals are placed in live-water tanks. Buyers should check for sexual maturity by observing the back under sunlight or using a flashlight on the abdomen. Mature broodstock are large, with full, dark green ovaries. They should also have intact limbs and active behavior.
After capture, broodstock can be placed in buckets with an air pump for short transport. For long-distance travel, 3-5 individuals per 20-liter plastic bag with seawater and ice packs help maintain a temperature of 18-21°C. When arriving at the farm, the bags are slowly introduced into the spawning pool to equalize temperature and salinity before releasing the shrimp.
Spawning and Hatching
Mature broodstock are selected and moved to spawning tanks. Spawning usually occurs at night. After transportation, most females spawn at the end of the day. If no eggs are produced within three days, they may not spawn again. Spawning pools should be spacious enough to allow free movement without wall collisions. A density of 1-3 tails per ton is ideal, with a water temperature of 26-29°C, salinity of 28-33 ppt, and a depth of 60-70 cm. After spawning, foam and mucus appear on the surface, which should be removed. In Taiwan, the spawning rate is around 70%, with each female laying 600,000 to over 1 million eggs. Eggs hatch into nauplii within 12-13 hours at 26-29°C, with a hatching rate of 70-80%. Nauplii are then counted and transferred to rearing tanks.
Shrimp Cultivation
1. Management of Infertile Larval Stage
newly hatched larvae measure 0.32-0.33 mm, with strong phototaxis but no feeding ability. No food is given during this stage, and water depth is maintained at 70 cm. Culture density ranges from 80,000 to 200,000 nauplii per ton. Larvae go through six molts before becoming encapsulated. At 27-29°C, this takes about 50 hours; at lower temperatures, it may take up to 110 hours. Survival rates during this phase are high, reaching 90%.
2. Management of Larval Stage
Larvae go through three molting phases. First-stage larvae are about 0.91 mm long and avoid light. Exposure to direct light causes them to stop feeding, become deformed, and die within 2-3 days. By the third stage, oxygen demand increases, requiring continuous aeration. Survival rates during this period are low, ranging from 30-60%, mainly due to poor feeding practices. Diatoms are the primary feed during this time.
3. Control of Post-Larval Stage
After three to four days of molting, larvae develop into squid-like forms. During this phase, their heads and tails bend at right angles, and they move backward rapidly. Survival improves, and they begin to consume zooplankton like rotifers and copepods.
4. Late Larval Management
At the late larval stage, the shrimp grow to about 5 mm and resemble adult shrimp. Water depth increases, and aeration is enhanced. By day five, they start settling on the bottom or attaching to the walls. Suitable conditions include 25-30°C and 14-25‰ salinity. After 5-10 days, they can be moved outdoors. Feed includes Artemia, rotifers, and copepods during early stages, with larger prey added later.
Shrimp Wintering
Large, well-developed black-shelled shrimp can be stocked at 100-150 per square meter in deep ponds with salinity of 15-25‰. Feeding is reduced during winter due to lower temperatures and slower metabolism. Overfeeding must be avoided to prevent water quality issues. It’s important to monitor dissolved oxygen, temperature, and salinity regularly to ensure optimal conditions.
Shrimp Transportation
Live shrimp should be transported quickly to rearing tanks by boat or car. For long-distance transport, use 20L plastic bags with 15-20L seawater, containing 3,000-5,000 shrimp per bag. Oxygenation and sealing are essential. In summer, add crushed ice to keep the temperature between 15-18°C. Upon arrival, do not pour directly into the tank. Instead, gradually introduce pond water into the bag to adjust temperature and salinity before releasing the shrimp. Under normal conditions, they will swim in groups and settle at the bottom.
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