First, the preparation of the fry cultivation pond is essential for ensuring a healthy and productive environment for fish seedlings.
(I) Fry Cultivation Pond
Select fish ponds with a reliable water source, clean water, and easy access for water inflow and drainage. The shape of the pond should be regular, preferably rectangular, with an area ranging from 1 to 3 mu (approximately 0.67 to 2 hectares). The water depth should be between 1 and 1.5 meters, and the bottom should be flat with a layer of sludge about 6 to 10 cm thick. It's important to remove any aquatic weeds or grasses that may grow in the pond. Before introducing fish, the pond should be thoroughly cleaned—remove excess silt, level the bottom, repair any leaks, and eliminate weeds along the embankments.
(b) Pond Clearing
Pond clearing should be done on a sunny day at noon to maximize the effectiveness of the disinfectants. There are several commonly used methods today:
1. Quicklime Quicklime reacts with water to form calcium hydroxide, releasing heat and raising the pH to above 11. This strong alkaline environment effectively kills harmful organisms such as parasites, pathogens, and larvae in the mud. It also neutralizes organic acids in the sludge, improving the water’s chemical balance and making it slightly alkaline. Additionally, quicklime acts as a fertilizer by releasing nutrients like nitrogen, phosphorus, and potassium, which promote plankton growth and enhance water fertility.
There are two main methods: dry pond treatment and wet pond treatment. For dry treatment, drain the pond to leave about 6–10 cm of water, dig some pits, spread the lime, and pour it into the pool. Use 50–150 kg per acre. After application, wait 7–10 days before stocking fish. Rotifer populations peak around 9–12 days after treatment.
2. Bleach (Calcium Hypochlorite) Bleach dissolves in water to form hypochlorous acid, which has strong bactericidal properties. It breaks down quickly, making it ideal for ponds that need to be stocked soon after treatment.
The dosage depends on the available chlorine content. For high-quality bleach (30% chlorine), use 4–5 kg per mu for dry treatment, and 13 kg per mu for a 1-meter deep water treatment (about 20 grams per cubic meter). Mix the bleach with a small amount of water to make a paste, then dilute and distribute evenly. Wait 3–5 days after treatment before adding fish. If the water quality is poor, increase the dosage accordingly.
3. Tea Seed Cake Tea seed cake is crushed and soaked in water. After one day, it can be used at a rate of 30 grams per cubic meter. At a water temperature of around 25°C, it fully decomposes within 7–8 days.
(3) Water Inlet and Base Fertilization
About 7–10 days before introducing fish fry, fill the pond with approximately 50 cm of water. Avoid filling too deeply, as this can slow water warming and affect water quality. Use a 60–80 mesh filter at the inlet to prevent wild fish and predators from entering. Apply base fertilizer promptly to provide food for the fry. After spawning, apply the base fertilizer to the fry pond, as rotifers reach their peak 4–6 days later, aligning with the timing of Brazilian carp fry emergence. Zooplankton succession typically starts with protozoa and rotifers, which are ideal for young fish. Base fertilizer is mainly made from composted green manure, applied at 150–200 kg per acre or the same amount of animal manure.
(D) Check Water Quality and Temperature
Before introducing fry, check the water quality and temperature to ensure that the disinfectant effects have faded and the conditions are suitable. To test, take a sample from the bottom of the pond and place 20–30 fry in it for a day. If they remain active, the chemicals have been neutralized. If quicklime was used, measure the pH. If it drops below 9, the pond is ready for fish. Always monitor the environment closely to maintain optimal conditions for the fry's growth.
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