First, the selection of pro-enlistment.
1. When choosing sea cucumbers for breeding, it's best to select those from a pool of mature individuals, as they tend to be more uniform and plump. The skin should be intact and clean, with each individual weighing between 250 and 350 grams. Their gonads should account for over 15% of their body weight, while the body wall should make up more than 50%. For every 1000 cubic meters of seedlings, around 400–500 individuals are needed, and each female should produce approximately 3 to 5 million eggs.
When the sea cucumbers are first caught, they are placed in long pots, typically in an elliptical or shoe sole shape. If the majority are females, the pot is usually elliptical; if males dominate, it tends to be longer. Choosing an elliptical or shoe sole shape better suits the nursery requirements.
2. For transportation, wet transport is preferred. It's best to transport them early in the morning when temperatures are low, traffic is light, and the environment is stable. Use plastic tanks of 50–70 liters each, filled with seawater from the original culture tank. Place a frozen bottle of mineral water inside to maintain temperature. Each tank can hold 25–35 individuals. Transportation should last no more than 10–12 hours, ensuring that few individuals become dirty during the process.
Second, the cultivation of parent stock and egg production.
1. Upon returning the parent stock to the nursery, maintain the same natural water temperature and salinity as the original pool. After they have expelled waste, change the water at 5 p.m. to stimulate spawning. The process of collection and transport acts as a strong stimulus, causing most of them to release eggs. These eggs are of high quality and do not require artificial breeding. If no eggs are produced, keep them for 3–5 days, changing water daily without excessive stimulation. On the fifth day, combine this with river flow and water current stimulation by placing the sea cucumbers in an empty nursery pond. After about 40 minutes, use a hose to gently impact the adults for 20 minutes. Spawning usually occurs 2–4 hours later, with peak activity between 9–12 p.m., so it's important to monitor closely.
2. Post-spawning care:
(1) Water requirements: The water must be filtered through a sedimentation tank and sand filter before passing through a 1000-mesh bag into the pool. Turbidity should be 50–100 mg/l. Add 3 g/m³ of EDTA sodium to chelate heavy metals. Maintain salinity between 27–32 and water temperature between 17–20°C. Add 2 g/m³ of antibiotics such as oxytetracycline or streptomycin.
(2) Pre-spawning management: Around 8–9 p.m., first collect male sea cucumbers, then after 0.5–1 hour, stimulate the females with sperm to induce spawning. At this point, males are separated into another pool for sale. Spawning ponds generally have a depth of 0.7 m. After spawning, all parents are moved to another pool for further cultivation. The egg pool is filled to 1.4 m. Perform micro-aeration and manual burping every hour to evenly distribute fertilized eggs and prevent localized oxygen depletion. This ensures sufficient dissolved oxygen, preventing egg death and poor larval hatching.
(3) The next morning, count the fertilized eggs. The density should be “small but not too large,†typically 8–10 per ml. If the density is too high, divide the pool using a siphon tube to transfer water into surrounding pools. Stir the water to ensure even distribution of eggs.
Third, the cultivation of planktonic larvae.
1. Selecting the time and method for larval rearing: Larvae should be collected before the development of fertilized eggs reaches the small ear-like stage and the opening of the digestive tract. To identify suitable larvae, observe when they start swimming and concentrate in the upper layers of the pond. Remove the aeration tube, wait an hour, and use a flashlight to check. When many larvae gather on the surface, use a 300-mesh sieve to collect them. Quantify and transfer them to nursery ponds, keeping the total density at 0.5–1 per ml.
2. Daily management:
(1) Water changes: On the first two days, gradually fill the pool with new water. Starting from day three, replace 60–70% of the water daily using a 250-mesh cage. Maintain natural water temperature and salinity. After each water change, add 3 g/m³ of EDTA sodium. Clean and dry the cages regularly.
(2) Feeding: Sea cucumber larvae cannot digest algae with cell walls. Studies show that mixing D. salina, C. capsularis, P. crinae, and P. tricornutum with marine red yeast provides good results. Dry yeast tablets for aquatic use can also be used effectively.
The quality of single-cell algae is crucial: the algae should have a bright color, no protozoa, and no aging cells. Protozoa may occasionally be present but should be monitored. If the water becomes cloudy or lacks light, protozoa may proliferate, so regular microscopic checks are essential. The culture density of single-cell algae should be: 1 million cells/ml for Dunaliella salina, 2×10² cells/ml for Phaeodactylum tricornutum, C. trichocarpa, and Chaetoceros.
Feeding methods vary depending on the larval stage. Small ear larvae begin with a small amount of Dunaliella salina and marine red yeast. Feed 3000 cells/ml daily, with 50% salt algae and 50% Chaetoceros. Moon ear larvae get 5000 cells/ml, with each type (Chaetoceros, Dunaliella, C. sulphurae) making up one-third. Big ear larvae receive 8000 cells/ml, with 40% Chaetoceros and Dunaliella, and 20% C. sulphurae. After three feedings, feed every 8 hours, only after water changes. No feeding is needed once larvae develop into the larva-shaped stage. Other options include marine red yeast, aquatic yeast tablets, and milk powder (0.1 g/m³).
3. Microscopic observation: After feeding, check under a microscope. If most larvae have clear food in their stomachs and visible bait particles, the feeding amount is appropriate. If food remains in the stomach after feeding, increase the amount. If larvae have full stomachs and feces, reduce the amount. Regular monitoring is essential to track development. After a few stages, Stichopus japonicus larvae develop into juveniles, taking about 11–13 days. Check each pool at least once daily to monitor growth and feeding. Normal development includes a daily increase of 50 microns in ear size. The water cavities evolve from round cysts in small ears to long cysts in middle ears, and finally to peanut-like shapes in big ears. By the end, larvae develop into juvenile sea cucumbers.
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