First, the preparation of the fry cultivation pond
(I) Fry Cultivation Pond
Select fish ponds with a reliable water source, clean water, and easy water inflow and drainage. The pond should have a neat shape, preferably rectangular, with an area of 1-3 mu and a water depth of 1-1.5 meters. The bottom of the pond should be flat with a moderate layer of sludge (6-10 cm), free from weeds and debris. Ensure that the pond is not leaking. Before introducing fish, clean the pond thoroughly by removing excess silt, leveling the bottom, repairing any leaks, and eliminating weeds along the embankments.
(b) Clearing the Pond
It is best to carry out the pond clearing on a sunny day at noon to maximize the effectiveness of the chemicals. Commonly used agents include:
1. Quicklime: When dissolved in water, quicklime forms calcium hydroxide, generating heat and raising the pH above 11. This creates a strong alkaline environment that effectively kills aquatic organisms, parasites, pathogens, and harmful larvae in the sediment. It also neutralizes organic acids in the sludge, improving the water’s pH balance and promoting plankton growth. Quicklime can also act as a fertilizer, releasing nutrients like nitrogen, phosphorus, and potassium back into the water. There are two methods for using quicklime: dry pond clearing and wet pond clearing. For dry clearing, drain the pond to about 6-10 cm, spread the lime evenly, and apply 50-150 kg per acre. After treatment, wait 7-10 days before stocking. Rotifers typically reach their peak 9-12 days later.
2. Bleach: When mixed with water, bleach produces hypochlorous acid, which has a strong disinfectant effect. It acts quickly and is ideal for ponds that need to be stocked soon after treatment. The dosage depends on the available chlorine content, usually around 30% for high-quality bleach. For dry pond clearing, use 4-5 kg per mu; for wet clearing with 1-meter depth, use 13 kg per mu (about 20 grams per cubic meter). Mix the bleach with a small amount of water first, then dilute it in the entire pond. Wait 3-5 days after treatment before introducing fish. If the water quality is poor, increase the dosage accordingly.
3. Tea Seed Cake: Crush the tea seed cake and soak it in water. Use 30 grams per cubic meter of water. At a water temperature of around 25°C, the cake will dissolve in 7-8 days.
(3) Water Inflow and Base Fertilization
Seven to ten days before introducing fry, fill the pond with about 50 cm of water. Avoid deep water to prevent slow warming and poor water quality. Use a 60-80 mesh filter at the inlet to prevent wild fish or predators from entering. Apply base fertilizer to provide food for the fry. After spawning, apply the base fertilizer to the fry pond to synchronize the rotifer peak with the fry's feeding period. Zooplankton succession typically starts with protozoa, followed by rotifers, cladocera, and finally copepods. Rotifers are especially important for Brazilian carp fry. Base fertilizer is mainly composed of green manure from Compositae plants, applied at 150-200 kg per acre or an equivalent amount of animal manure.
(D) Check Water Quality and Temperature
Before introducing fry, check the water quality and temperature to ensure that chemical residues have disappeared and that the temperature is suitable. To test for residual chemicals, place 20-30 fry in a container of bottom pond water and observe for one day. If they remain healthy, the chemicals have been neutralized. If lime was used, measure the pH. A pH below 9 indicates that the treatment is complete. Proper preparation ensures a safe and productive environment for fry growth.
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