Loach high density and high efficiency

In the past two years, a significant rise in aquaculture has taken place in the surrounding areas of Lianyungang City, with thousands of tons of loach being exported annually to South Korea and Japan. In 2004, we conducted an intensive muddy loach culture experiment on a 20-mu pond in Gifu Prefecture, which yielded excellent economic returns. Below is a detailed summary of the test. First, materials and methods. 1. Pond Conditions: A total of 10 ponds were selected, each measuring 2 acres. The ponds were oriented east-west to maximize sunlight exposure. The soil was clayey, with a sludge layer of 20-30 cm at the bottom. The pond depth ranged from 70-100 cm, with a water depth of 40-50 cm. The bottom was flat and easy to manage for water exchange and drainage. To facilitate harvesting, a fish slide was installed near the outlet, covering about 4% of the pond's bottom and extending 30-35 cm deeper than the pond floor. To prevent loach from escaping, a 20-mesh polyethylene net was buried 30 cm deep around the pond and extended 30 cm above the water surface. A similar net was also installed at the water outlet to block escape routes. 2. Pond Preparation and Fertilization: Ten to fifteen days before stocking, the ponds were thoroughly cleaned and disinfected. After draining the water, any leaks were checked, and lime (150 kg per acre) was applied for disinfection. Once the lime was spread evenly, the pond was refilled. One week later, fresh water was introduced through a sieve to prevent wild fish from entering. Basal fertilizer was then added, with 160 kg of chicken manure per acre used to cultivate plankton for the loach. The water clarity was maintained at approximately 20 cm, with a yellow-green color indicating optimal conditions. 3. Stocking: Based on local farming practices, we tested different stocking times, sizes, and densities to identify the most effective model. Wild loach purchased from Hubei and Henan cost an average of 7.6 yuan per kilogram. The seedlings were released between April 20 and June 28, and were soaked in a 2-3% saline solution for 5-10 minutes before being stocked. 4. Daily Management: (1) Feeding: Artificial feed was primarily used, with feeding once daily in the afternoon. Loach-specific feed was used, with the daily ration ranging from 1.5% to 8% of the loach’s body weight, depending on water temperature. When the temperature was below 20°C, feeding was reduced to 1.5%-3%, while at 23-30°C, it increased to 5%-8%. At lower temperatures, up to 28%-30% of the feed could be provided, and at optimal temperatures, 32%-34% was given. Normally, feeding occurred twice daily—60%-70% in the morning and 30%-40% in the afternoon. When water temperatures exceeded 30°C or dropped below 10°C, feeding was reduced or stopped. Overfeeding was avoided to prevent digestive issues. We implemented a “four settings” feeding strategy to control portions and reduce gluttony. (2) Water Quality Control: The water quality should remain “fat, live, tender, and cool.” Transparency was kept around 30 cm, dissolved oxygen levels above 3.5 mg/L, and pH between 7.6 and 8.8. Regular monitoring of water color was essential. If the water became too dark or thick, new water was added or replaced. In the early stages, water was mainly changed, while in later stages, it was changed every 2-3 days, with 20%-50% of the water volume replaced each time. Food tables were cleaned daily, and every 20 days, 20 grams of quicklime per cubic meter was applied. Bleach at 1 g/m³ was used every half month for disinfection. (3) Disease Prevention: Povidone iodine was regularly used at 1% concentration, with the water reaching 0.5 g/m³ to maintain hygiene. (4) Trapping: Effective trapping methods were employed, with some ponds achieving a catch rate of over 60%. Once most loach were caught, they were harvested using nets. Second, the test results showed that the mud catching period ran from early October to early November. 1. Seedling yield was 29,100 kg, with a total harvest of 36,324 kg. The average weight gain was 24.9%, with the highest reaching 64.4% and the lowest at 0.3%. The average size of seedlings was 109/kg, and at harvest, it was 69/kg. 2. Economic Benefits: With 20 acres of 10 ponds harvested, 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 method is more of high-density stock raising rather than pure high-density culture. The breeding cycle typically lasts over three months, with a weight gain rate of about 30%, which is significantly lower than other farmed species. However, feed costs were substantial due to high stocking density and limited environmental improvements, leading to slower growth. The main economic benefit came from the price difference of loach, rising from 7.6 yuan/kg at stocking to 18.45 yuan/kg at sale—a 2.4-fold increase. High survival rates were crucial for good economic returns. 2. Under these farming conditions, the timing, size, and density of stocking directly affected profitability. We observed that during the spawning season (April to early May), many loach had already matured, making them vulnerable to stress from feeding and transport, leading to high mortality. Loach with 110-130 tails per kilogram were ideal for stocking, as larger ones were often mature and had higher death rates, while smaller ones did not meet market standards. Stocking density should not exceed 2000 kg/mu, ideally between 1300-2000 kg/mu. The best time to avoid the breeding season was to plant seedlings after 2-3 months or mid-June. 3. The next step is to conduct low-density, small-scale experiments with loach. It is recommended to stock 40,000-80,000 oyster-like loach per mu, each 3-4 cm in size, before March each year. This approach would enhance growth, improve feed efficiency, meet market demands, and reduce disease and mortality associated with feeding and transport.

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