Loach high density and high efficiency

In the past two years, there has been a significant rise in aquaculture around Lianyungang City, with thousands of tons of eel being exported annually to South Korea and Japan. In 2004, we conducted an intensive muddy culture experiment in a 20-mu pond located in Gifu Prefecture, which yielded excellent economic returns. Below is a detailed summary of the test. **First, Materials and Methods** 1. **Pond Conditions**: Ten ponds were selected, each covering 2 acres, oriented east-west to maximize sunlight exposure. The soil was clayey, with a sludge layer 20–30 cm deep and a water depth of 40–50 cm. The pond bottom was flat, making it easy to manage. A fish slide was installed near the outlet to aid in harvesting, extending about 4% of the pond's area and 30–35 cm deeper than the bottom. To prevent eels from escaping, a 20-mesh polyethylene net was buried 30 cm deep around the pond, extending 30 cm above the water surface. A similar net was also installed at the water outlet. 2. **Pond Preparation and Fertilization**: Before stocking, the ponds were cleaned and left for 10–15 days. After draining the water, any leaks were checked, and 150 kg of lime per acre was used for disinfection. One week later, fresh water was added through a sieve to prevent wild fish from entering. Basal fertilizer was applied at 160 kg of chicken manure per acre to cultivate plankton for feeding. Water transparency was maintained at around 20 cm, with a yellow-green color. 3. **Stocking**: Eel seedlings were sourced from Hubei and Henan, costing an average of 7.6 yuan/kg. Stocking took place between April 20 and June 28. Before release, the seedlings were soaked in a 2–3% saline solution for 5–10 minutes. 4. **Daily Management**: - **Feeding**: Mainly artificial feed was used, with one feeding session in the afternoon. Daily feed amounted to 1.5–8% of the eel’s body weight, depending on water temperature. Feeding rates increased with higher temperatures, but care was taken to avoid overfeeding, especially during high-temperature periods. Feed was distributed evenly across multiple stations to prevent gluttony. - **Water Quality Control**: The water should remain “fat, live, tender, and cool,” with a transparency of 30 cm, dissolved oxygen above 3.5 mg/l, and pH between 7.6 and 8.8. Water was changed regularly, especially in later stages of growth. Lime and bleach were used periodically for disinfection. - **Disease Prevention**: Povidone iodine was used at 1% concentration, with a final concentration of 0.5 g/m³ in the pond. - **Harvesting**: Trapping proved effective, with more than 60% catch rate in some ponds. Once most eels were caught, they were netted out. **Second, Test Results** The eel harvesting period ran from early October to early November. 1. **Yield**: A total of 29,100 kg of seedlings were stocked, resulting in 36,324 kg harvested. The average weight gain was 24.9%, with the highest reaching 64.4% and the lowest 0.3%. The average size at stocking was 109/kg, while at harvest it was 69/kg. 2. **Profitability**: With 20 acres of 10 ponds, the average selling price was 18.45 yuan/kg, generating a production value of 671,273.9 yuan and a profit of 2,962,224.2 yuan. The highest profit per pond reached 42,244.4 yuan, while the lowest was 1,253.5 yuan. **Third, Analysis and Discussion** 1. This aquaculture model is more of a high-density stock raising rather than traditional intensive farming. The breeding cycle typically lasts over three months, with a weight gain rate of about 30%, which is lower than other cultured species. However, feed costs are significant due to high density and large-scale stocking, leading to poor water quality and slower growth. Economic benefits mainly come from the price difference—eels were sold at 18.45 yuan/kg, up from 7.6 yuan/kg at stocking. High survival rates are crucial for profitability. 2. Stocking time, size, and density directly impact economic returns. We found that eels stocked in April to May often matured too early, leading to high mortality. The ideal size for stocking is between 110–130 tails per kilogram, avoiding both early maturity and small sizes. Stocking density should not exceed 2000 kg/mu, ideally 1300–2000 kg/mu. It is best to avoid the spawning season and instead plant seedlings after 2–3 months or in mid-June. 3. The next step is to conduct low-density, smaller-scale experiments. Stocking 40,000–80,000 eels per mu, each 3–4 cm in size, before March could improve growth, feed efficiency, and market compliance while reducing disease risks.

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