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Cultivation Techniques of Yellow Catfish Fry
Stingray fry have specific biological needs that must be carefully managed to ensure their healthy development. First, their living environment plays a crucial role in their survival. These young fish are sensitive to environmental changes and require stable water conditions. The ideal pH range is 7.0, and deviations below 6.5 or above 8.0 can lead to health issues such as skin discoloration, increased mucus production, and even infections. The optimal water temperature for growth is between 22°C and 27°C, with a minimum of 15°C and a maximum of 32°C. Water quality should maintain at least 5.0 mg/L of dissolved oxygen to support their metabolic needs.
In terms of feeding, stingray fry start with endogenous nutrition, relying on the yolk sac for the first few days. By day three, they begin to transition to exogenous feeding, and by day five, the yolk sac is completely absorbed. At this point, the fry are about 8 mm long and rely entirely on external food sources, such as rotifers and small copepods. This early stage requires careful management to ensure proper nutrition and growth.
Growth rates are rapid during the initial stages, with fry increasing their weight tenfold within 30 days. However, as they grow older, their growth rate gradually slows down. This makes it essential to provide adequate nutrition and maintain optimal conditions throughout their development.
When setting up a cultivation pond, several factors must be considered. The pond should have a reliable water source, good drainage, and a suitable shape—preferably rectangular and oriented east-west. The size should be between 1 and 2 mu (approximately 0.67 to 1.33 hectares), with a depth of 0.8 to 1.2 meters. The bottom should be flat and free of debris, and the walls should be sturdy to prevent leaks. Newly constructed concrete ponds need to be thoroughly cleaned and allowed to cure before use, with a pH between 7.0 and 7.8.
Preparation of the pond is equally important. For earthen ponds, old silt should be removed, the bottom leveled, and any cracks filled. Concrete pools should be scrubbed and left to air dry. Lime is often used to disinfect the area and eliminate unwanted organisms. Water quality is critical, especially for young fry, which are vulnerable to predators and pollutants. The water should be clean, and the inlet should be filtered with a 40-mesh sieve to prevent unwanted organisms from entering.
Transporting the fry requires care. Before moving, the fry should be acclimated for 3–5 hours in a holding cage. They are then placed in oxygenated plastic bags, each containing 8–9 liters of water, with about two-thirds of the bag filled. These bags are packed in boxes and transported for up to 15 hours, ensuring no leaks occur during transit.
Once in the pond, the fry need to be introduced gradually. The water temperature should match, and the fry should be slowly released into the holding box to adjust. After acclimation, they can be fed with cooked egg yolk passed through an 80-mesh sieve. Daily feeding with soybean milk is also necessary, with 15–17 kg per mu (about 1 kg of dry soybeans) distributed in the morning, afternoon, and evening.
Monitoring the pond regularly is essential. The number and type of rotifers should be checked using a low-power microscope. If cysticercus rotifers appear, it indicates the peak is ending, and organic fertilizer should be added to maintain productivity. Water levels should be kept at 50–60 cm, and partial water changes (10–20 cm) should be done every six days.
Oxygen levels must be maintained, and net exercises should be conducted to improve the fry’s strength and adaptability. Algae should be removed regularly to prevent overgrowth. Daily records of fish behavior, feeding, and water quality should be kept, along with weather and temperature data. This helps in making timely adjustments and planning for future seasons.