(1) Nursery Pond:
Black carp fry can be raised both indoors and outdoors. For indoor cultivation, a concrete pond of 1.5 to 3.0 square meters with a water depth of 1 meter is commonly used. The stocking density should be between 30,000 to 100,000 fry per cubic meter. The water in the pond should remain still but be exchanged 1 to 2 times daily, with each exchange replacing about half to one-third of the total volume. Alternatively, you can use 1-square-meter cages with a water depth of 0.8 meters under micro-flow conditions. Regular cleaning and waste removal from the cages are essential for maintaining good water quality.
Outdoors, black carp fry are typically raised in earthen ponds ranging from 100 to 1000 square meters, with a water depth of 0.7 to 1 meter. Before introducing the fry, the pond must be thoroughly cleaned using bleach to eliminate potential predators and harmful organisms. A week before breeding, the pond should be fertilized to promote the growth of natural food sources such as plankton. New water added to the pond must be filtered through an 80-mesh sieve or a sand filter to prevent contamination.
(2) Feeding and Food Amounts:
Black carp fry start feeding on the third day after hatching. Proper nutrition is crucial for their survival and development. Initially, they are fed with oyster eggs or their larvae, or high-temperature cultured rotifers at a concentration of around 5 cells per milliliter. As the fry grow, egg yolk and other supplementary foods can be introduced to support their transition to open feeding. It's important to note that the rotifers must be cultivated with chlorella for at least 6 hours to ensure they are nutritious and healthy.
Once the fry reach the juvenile stage, they can be fed with Artemia nauplii at a density of 0.1 to 0.5 per milliliter, along with small crustaceans, fish meal, shrimp, and commercial feed. Feeding should be done in small portions, 5 to 6 times a day, to avoid overfeeding and maintain clean water conditions.
(3) Water Quality:
Maintaining optimal water quality is essential for the successful rearing of black carp. The water should be clean, fresh, and have a salinity of 18 to 25 parts per thousand. The ideal temperature is around 18°C, with a pH between 7.8 and 8.5. Dissolved oxygen levels should be kept above 5 mg/L, and ammonia nitrogen content must be below 0.1 mg/L. To keep the water clean, debris should be removed from the nursery tanks 1 to 2 times daily. The tank bottom should be regularly washed, and water changes combined with aeration should be performed frequently.
During the first 7 to 10 days after hatching, it's best to use still water to protect the delicate fry. After this period, gradual water changes and aeration can begin, increasing the water exchange rate from 20% up to 100–300%. Aeration should start from the surface and gradually increase as the fish grow. This helps maintain stable and healthy water conditions throughout the rearing process.
(4) Stocking Density:
The stocking density significantly affects the growth and survival of black carp fry. When the fry are less than 0.7 to 1 cm in length, a higher density of 3 to 50,000 per cubic meter is recommended. However, once the fry grow beyond this size, the density should be reduced to 0.2 to 10,000 per cubic meter to prevent overcrowding and ensure proper growth. Monitoring and adjusting the stocking density based on the fry’s development is key to achieving high survival rates and healthy growth.
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