(1) Nursery Pond:
Black carp fry can be raised both indoors and outdoors. For indoor cultivation, a concrete pond with an area of 1.5 to 3.0 square meters and a water depth of 1 meter is commonly used. The stocking density ranges from 30,000 to 100,000 fry per cubic meter. Water should be changed or exchanged 1 to 2 times daily, with each exchange amounting to 1/2 to 1/3 of the tank's volume. Alternatively, 1 square meter cages with a water depth of 0.8 meters can be used under micro-flow conditions, ensuring regular cleaning and waste removal from the cages.
Outdoor rearing typically takes place in earthen ponds ranging from 100 to 1000 square meters with a water depth of 0.7 to 1 meter. Before introducing fry, the pond must be thoroughly cleaned using bleach to eliminate predators and harmful organisms. A week before hatching, the pond is fertilized to promote the growth of natural food sources such as plankton. New water must be filtered through an 80-mesh net or a sand filter to prevent contaminants from entering the system.
(2) Feeding Practices and Amounts:
Black carp fry start feeding on the third day after hatching. Proper nutrition is crucial for their survival. Initially, they are fed with oyster eggs, their larvae, or rotifers cultivated at high temperatures. At a concentration of 5 cells per milliliter, the fry can be supplemented with egg yolk and other suitable foods to help them transition from the open feeding stage. It's important to note that the rotifers must be cultured with chlorella for at least 6 hours to ensure their nutritional value.
As the fry grow into juveniles, their diet shifts to Artemia nauplii at a concentration of 0.1 to 0.5 per milliliter, along with small fish, shrimp, and commercial feed. Juveniles can also consume copepods, fish meal, and compound feed. Feeding should be done in small portions, 5 to 6 times a day, to avoid overfeeding and maintain water quality.
(3) Water Quality Management:
Maintaining optimal water conditions is essential for black carp rearing. The water should be clean, fresh, and have a salinity between 18 to 25 parts per thousand. The ideal temperature is around 18°C, with a pH range of 7.8 to 8.5 and dissolved oxygen levels above 5 mg/L. Ammonia nitrogen levels should remain below 0.1 mg/L. To keep the nursery water clean, debris should be removed 1 to 2 times daily, and the bottom of the tanks should be regularly scrubbed.
Water changes and aeration are critical during the early stages. In the first 7 to 10 days after hatching, it’s best to use static water to reduce stress on the delicate fry. After this period, gradual water exchanges begin, increasing from 20% up to 100-300%, depending on the development stage. Aeration starts from surface-level and gradually increases as the fish grow. This helps maintain good oxygen levels and supports healthy growth.
(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. Once they grow beyond this size, the density should be reduced to 0.2 to 10,000 per cubic meter to prevent overcrowding and ensure adequate space for development. Monitoring and adjusting the density regularly is essential for successful rearing.
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