First, manage the yolk sac stage of the fry. Newly hatched fry are still nourished by their yolk sac and have weak bodies with large yolk sacs. They are not able to swim freely on their own and rely on water currents to move. Therefore, they need to be carefully raised. Once the fry absorb their yolk sacs and develop some swimming ability, they can be transferred to a holding pool. This stage usually occurs around 7 to 8 days after hatching, with the fry reaching a length of about 10 to 14 mm.
Second, raising the fry properly is crucial.
1. Seedling Holding Facilities: The main facilities used for holding fry include flowing cement tanks and cages. Cement pools can be round or square, typically ranging from 3 to 5 cubic meters in size. The water volume should not be too large. Inlet and outlet pipes must be fitted with 40- to 50-mesh screens to prevent fry from escaping. Cage dimensions are commonly 2 meters in length, 1 meter in width, and 0.5 meters in height.
2. Raising Methods:
(1) Cement Tank Holding: Place the yolk-sac fry into a flowing cement tank, keeping a density of 25,000 to 30,000 fry per cubic meter. For the first 3 to 4 days, maintain continuous water flow to ensure sufficient dissolved oxygen. After 4 to 5 days, when the fry become more active and start swimming freely, you can begin feeding them zooplankton or artificial micro-food. Live food like red worms and midge larvae are ideal. Feed them several times a day, ensuring they eat well until their body color changes from reddish to dark gray. Throughout this period, maintain a gentle water flow, high dissolved oxygen levels, and clean water. Regular disinfection with potassium permanganate at a concentration of 8 g/m³ is also necessary.
(2) Cage Holding: Use 40- to 50-mesh nylon mesh to construct a cage measuring 2 meters long, 0.8 meters wide, and 0.5 meters deep. Place the cage in a disinfected pond 3 to 4 days before introducing the fry, allowing it to soak and soften, which reduces friction and protects the fry. The temporary water should have a transparency of over 50 cm and a rich supply of zooplankton. A density of 5,000 to 10,000 fry per square meter is recommended. The cage’s outlet should be positioned 4 to 5 cm below the water surface, enabling the fry to swim out naturally. After 4 to 5 days, most fry will leave the cage. Any that remain should be manually released. Monitor the water quality regularly, keep it clear, maintain dissolved oxygen above 5 mg/L, and clean the cage frequently. Check for any damage to prevent fry from escaping.
Qingdao Beautiful Skin Biotechnoly Co., Ltd , https://www.hafilleresthetic.com