Shed cultivation of Penaeus vannamei desalinated seedlings

Greenhouses can be either permanent steel-concrete structures or simpler plastic greenhouses, depending on the scale and budget of the operation. The ideal size for a greenhouse is typically between 0.5 to 3 acres, with a pool depth of around 1.5 meters. One-fifth of the water in the greenhouse should be reserved as a separate reservoir to ensure stable water supply and oxygenation. For intensive shrimp farming, an aerator must be installed to maintain adequate dissolved oxygen levels in the cultivation area. The greenhouse should have access to a reliable source of fresh water, such as underground drinking water, along with a storage system that allows for heating and aeration of well water. Before introducing seedlings, it's essential to disinfect the pond thoroughly. Next, water should be drawn in advance according to the specific salinity and water quality needs of the seedlings. If the greenhouse uses desalinated water, fresh water should be stored in the pond for later use. It’s also important to cultivate natural food sources. After filling the pond, appropriate fertilizers should be applied based on the nutrient levels in the water. A common ratio is 10 parts urea to 1 or 2 parts superphosphate, and human urine can also be used after fermentation. If the water is clear, diatoms can be introduced to enhance food availability. Staged fertilization helps achieve a yellow-green or light brown water color with a transparency of 0.3–0.4 meters. If clump-like organisms are present, they can serve as additional food sources. Rotifers or Artemia eggs may also be added before the seedlings arrive to support their growth. Monitoring water temperature and maintaining optimal water quality is crucial. The water temperature should be above 26°C, similar to that in nursery units. Salinity should match or be slightly lower than that of the incoming water, while pH should remain within 8.0 ± 0.3. If pH exceeds 8.6, water should be replaced or adjusted with organic weak acids like acetic acid. If pH drops below 7.5, lime water can be used to raise it. When selecting shrimp larvae, it’s important to choose healthy individuals. For Penaeus vannamei, larvae should be at least 3 days old, with a body length of 0.6 cm or more, free from disease and parasites. Shrimps that have been desalinated should be at least 1 cm long and no older than 10 days. During transportation, thermal-insulated foam boxes or non-toxic plastic bags with pure oxygen are commonly used. Seedlings should be gradually acclimated to the greenhouse water before release. The stocking density depends on the size of the greenhouse and the stage of the seedlings. Typically, the effective water surface can hold 1 to 2 million seedlings per acre. Lower densities allow for better growth when seedlings reach 2.5–3 cm, while higher densities require earlier harvesting at 2.0–2.5 cm to avoid reduced survival rates. Desalination of shrimp seedlings should begin three days after delivery. The salinity should be reduced gradually at a rate of 2‰ per day to help the shrimp adapt and develop osmoregulation abilities, thereby increasing survival rates. After one week, the desalination rate can be increased slightly. Throughout the process, water temperature should be maintained between 26°C and 32°C, ideally 28°C–30°C, with minimal fluctuations. pH should remain stable between 8.0 and 8.3 to reduce stress and improve survival. During shrimp cultivation, feeding is critical. Fresh fish should be provided at about 40% of the total shrimp biomass daily, adjusting feed amounts based on consumption and stomach fullness. Feed options include rotifers, brine shrimp, washed fish, freshwater fish, and artificial diets. Feeding should occur six times a day, every four hours, with the largest portion given in the evening. Water quality monitoring is essential throughout the growing period. Water depth should be 0.7–1 m in the early stages and 1.5 m in later stages. Water temperature should be kept between 28°C–30°C, not dropping below 26°C or rising above 32°C. Water color should be yellow-green, light brown, or yellow-brown, with a transparency of 30–40 cm. pH should stay within 8.0 ± 0.3, and dissolved oxygen should be between 0.5–0.7 mg/L, with oxygenation agents used if necessary. Ammonia nitrogen levels should remain below 0.5 mg/L, and zeolite powder can be used if levels rise. To prevent disease, maintaining clean water, stable substrate, and high-quality feed is fundamental. Given the high density and short cultivation cycle in greenhouses, extra precautions are needed. Sodium EDTA can be used early to prevent heavy metal toxicity. Photosynthetic bacteria should be introduced to break down organic waste. Additionally, feed should be treated with allicin and vitamin C to boost shrimp immunity and protect against viruses and pathogens.

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