Industrialized Seedling Rearing Technology for Whiteleg Shrimp

AbstractWhiteleg shrimp farming requires thorough knowledge of broodstock rearing, broodstock gonad maturation, induced mating and spawning, fertilized egg collection and hatching, larval rearing conditions, and seedling management techniques. To achieve fast shrimp growth, strict requirements apply to water quality, stocking density, pond water depth, and feed feeding.

1. Broodstock Rearing

For broodstock rearing, select individuals weighing more than 40g and about 13cm in body length. The broodstock are placed in earthen ponds for maturation and temporary holding. The stocking density is controlled at 20 shrimp per sq m, with a female-to-male ratio of 1:15. The suitable water temperature is about 28°C, and the salinity is about 35‰. Feed once each morning and evening, with the feeding amount at about 20% of the broodstock body weight.

2. Using Eyestalk Ablation to Induce Broodstock Gonad Maturation

Use right eyestalk ablation to promote broodstock maturation, ablating the right eyestalk uniformly in both female and male shrimp. After ablating the right eyestalk, rear them in earthen ponds for a period, then remove the left eyestalk to induce gonad maturation in both female and male shrimp. After maturation promotion, inspect the shrimp every 3 days. When maturity reaches stage IV or above, net the broodstock out and place them in an induction pond for temporary holding.

3. Mating and Spawning

When the ratio of female to male broodstock is 1:3 and the temporary holding density is 15 shrimp per cubic meter, use artificial induction combined with natural mating to achieve mating and spawning. Female shrimp generally spawn during the period from night to early morning.

4. Collecting Fertilized Eggs for Hatching

After the female shrimp spawn, check the egg development condition carefully, then collect, wash, and count the eggs, and place the eggs in dedicated buckets for hatching. The hatching temperature should be controlled at about 30°C. The hatched larvae should be collected by the light-attraction method.

5. Conditions for Larval Rearing

The basic conditions for whiteleg shrimp development are: density controlled at 120,000 larvae per cubic meter, water depth controlled at about 1.5m, water temperature maintained at about 29°C, water salinity controlled at 32‰, pH maintained at about 8.1, and dissolved oxygen no lower than 6mg/L. The following aspects also require attention.

1. Water Quality Treatment

Larval shrimp rearing has high water quality requirements. Seawater pumped from the sea area must be strictly filtered, darkened, and subjected to two-stage sand filtration. Before entering the rearing pond, it must be filtered once more with a filter bag. To prevent heavy metal toxicity, chelating agents can be added to the water for water quality treatment.

2. Feeding Feed

For the zoea stage (Z), the feeding amount for Z1 and Z2 is 30,000-50,000 cells/mL. If artificial feed is used, it must be rinsed through silk cloth and evenly scattered into the pond, feeding 3-5g per 10,000 larvae. For the Z3 stage, the daily feeding amount is 4-5g per 10,000 larvae.

For the mysis stage (M), M1 and M2 are mainly fed rotifers, and the rotifer density in the water should be maintained at 5-10 per mL. M3 is mainly fed Artemia nauplii, and the density should be maintained at 1-3 per mL.

For the postlarval stage, the feeding is mainly artificial feed, with a feeding amount of 15-18g per 10,000 larvae. In the late postlarval stage, an appropriate amount of egg yolk can also be used for feeding.

6. Seedling Management

1. Regularly examine plankton under the microscope. The species and quantity of plankton need regular microscopic examination to observe the vitality and development of larvae in the pond and to calculate the number of larvae, so as to promptly keep track of the number of larvae at each stage and the survival rate.

2. Regularly measure various indicators in the water. Regularly test the pH value, water temperature, and dissolved oxygen in the rearing pond, adjust the water temperature required by the larvae as needed, ensure the relative stability of specific gravity, and at the same time always ensure sufficient dissolved oxygen.

3. Promptly discharge waste and change water. Observe the development of seedlings in the seedling pond, promptly discharge wastewater, and add fresh seawater. Ensure the amount of fresh seawater needed by zoea larvae and nauplius larvae. During the postlarval stage, the seawater exchange volume should be appropriately increased, and a water exchange volume of 50% in the later period is most suitable.

7. How to Manage the Grow-out Period

1. Setting Up the Culture Pond

The culture pond is preferably rectangular, with the surroundings built with concrete, and a depth of about 3.5m. A drainage outlet is set in the center of the pond, and the surroundings of the pond also need a place with sufficient freshwater supply.

2. Stocking Seedlings

Before stocking seedlings, the pond should be thoroughly cleared, and the sludge and weeds at the bottom of the pond should be completely removed. Repair the surroundings of the pond, install gate nets at the inlet and outlet, and disinfect with quicklime to kill miscellaneous fish and other harmful organisms.

After the pond is disinfected, inject water to a depth of 1.5m, add brine and industrial salt to make the pond water specific gravity reach 1.016 and the pH value about 8.6, then add urea and superphosphate to cultivate natural food organisms. For shrimp seedling stocking, select about 700,000 high-quality shrimp seedlings with a body length of about 1cm, with a density controlled at 30,000 per mu. After stocking in freshwater for 10 days, feed artificial feed and turn on the aerator to ensure sufficient dissolved oxygen.

3. Daily Management

7 days after stocking, begin feeding artificial compound feed 3 times a day, in the morning, evening, and at night, with the feeding amount determined according to the feeding condition of the shrimp. Feed more in the morning and evening and less at night. When water quality is good, more can be fed; when water quality is poor, less should be fed. On cloudy and rainy days and in cold weather, less should also be fed. During the shrimp growth process, the feeding amount should also change according to the body length of the shrimp.

Water depth requirements for whiteleg shrimp at each growth stage: in the early stage, the water depth is about 1.5m; in the middle stage, the water depth is controlled at about 2m; in the late stage, the water depth is about 2.8m. In the early culture period, the pond water is mainly freshwater. In the middle and late culture periods, the water exchange volume should be determined according to the pond water quality and the growth condition of the shrimp seedlings. In the late culture period, it should gradually be changed to seawater until harvest and market. The water body should be kept clean at all times, debris should be removed promptly, and the pond bottom should also be kept clean, which is more conducive to shrimp growth.

Aeration pipes should be properly arranged at the bottom of the culture pond, a generator should be equipped, and a blower should be used for aeration to achieve the oxygen level required by the shrimp. Persist in patrolling the pond in the morning, midday, and evening, check that facilities are complete, record the water temperature, salinity, dissolved oxygen, and other factors for shrimp growth, and conduct sampling inspections of the shrimp in the pond every half month to promptly understand the shrimp growth rate and adjust the daily feeding amount at any time.

4. Disease Prevention and Control

During the culture period, strictly adhere to principles such as “prevention first, early treatment of disease”, regularly use biological agents, and add VC, immune polysaccharides, etc. to the feed to enhance shrimp immunity. Every half month, mix decocted Chinese herbal medicines such as mulberry leaves, Phellodendron chinense, and rhubarb into the feed for feeding. When conditions permit, the morning and evening meals can be fed with 10‰ imported fish oil and 1‰ stabilized VC combined with feed. This can strengthen the shrimp constitution, improve immunity, and promote rapid growth of whiteleg shrimp.