A Complete Analysis of the Mysteries of Farming Rice Field Eels in Membrane Ponds
Q: Could you introduce the technical features of still-water, soil-free rice field eel farming in anti-seepage membrane ponds?
A: 1) Low pond construction cost: the cost per sq m is less than 25 yuan (including pipeline facilities, labor costs and plastic film, etc.), the service life is 8 years, and construction is fast, overcoming the shortcomings of high cost and slow construction of cement ponds, at about 1/3 to 1/2 of the cost of cement ponds. It is also easy to maintain: once the film develops cracks or holes, it can be welded with a plastic hot-air welding gun; 2) Good reclaimability: if farming is discontinued, the original land properties can easily be restored, making it suitable for developmental use of collectively owned construction land after land transfer; 3) Farming is possible in all four seasons, avoiding the shortcomings of cage farming, such as the concentrated season (June to September) and high fry prices; the price per kg of fry can be reduced by 10 to 20 yuan. Overwintering is relatively easy and the water temperature is relatively high, so the eels can be sold around the Spring Festival when the price of commercial eels is highest, earning about 10 yuan more per kg of eel; 4) Low water use and wide adaptability: it can be used for both courtyard farming and large-scale farming; both indoor farming (including balconies and rooftops) and outdoor farming; both freshwater farming and saline-alkali land farming; 5) Labor-saving: for the same farming area, the labor used is only 1/3 of that for cage farming, and operations are safe; 6) When pests and diseases occur, they are easy to observe and measures can be taken in advance; spraying liquid medicine leaves no dead corners, disease control results are good, and drug costs are low. The pond walls are very smooth, so they will not damage the mucous membrane on the body surface of rice field eels, which can prevent fish diseases, and the survival rate is 10% higher than that of cages. 7) In low-temperature seasons, the water temperature is often higher than in cement ponds, which helps extend the feeding period of rice field eels. The quality of the farmed rice field eels is easy to control, water changes and sludge removal are thorough, the water body lasts a long time, there is no pollution to the water body, and the income from by-products such as loaches and small miscellaneous fish is 20 yuan per sq m.
Q: Do membrane ponds need frequent water changes? What is "aquaponics" about?
A: Membrane pond farming uses specially made fish nests instead of mud and uses aquatic plants and water quality improvers to improve water quality. Although the pond is relatively small, the water quality can be maintained in a stable state. By growing vegetables on the water surface, such as water dropwort and water spinach, the goal is ultimately achieved that no more water changes are needed for eel farming and no more fertilizer is needed for vegetable growing. Generally, we require changing the water once every 30 days in spring and autumn, while in summer it is usually enough to change the water once every half month. At ordinary times, it is only necessary to add some water lost to evaporation. The patented "aquaponics" technology is a major discovery by Dr. Zhou Wenzong in the field of ecological farming. In an aquaponics system, aquatic vegetables can absorb nutrient salts such as nitrogen and phosphorus discharged from fish metabolism in the farming water, remove 80 to 90% of suspended matter and 70 to 80% of organic matter in the water, reduce biological oxygen demand by 90 to 95%, and keep the pH value of the water within the standard range. Aquatic vegetables can also disinfect the water body (the plant bactericides secreted by their root systems can kill 90 to 95% of pathogenic bacteria), giving the fish pond water body self-repairing capacity. The complete compound feed configured for this aquaponics system contains high-quality raw materials such as fish meal and bone meal, which exactly supplements the supply of trace elements. The vegetables and fruits successfully grown include water spinach, water dropwort, lettuce, tomato, cherry tomato and strawberry.
Q: Can anti-seepage membrane really guarantee a service life of eight years?
A: In 2005, we began using smooth-surface and rough-surface HDPE anti-seepage membrane with a thickness of 0.35 mm for farming. The anti-seepage membrane is made from high-quality high-density polyethylene virgin resin produced by three-layer co-extrusion technology using fully automatic Italian geotechnical production equipment, and is produced according to the American GRI standard and ASTM testing standards. It is non-toxic, environmentally friendly and quick to install. Its main components are 97.5% high-density polyethylene and about 2.5% auxiliary materials such as carbon black, anti-aging agents, antioxidants, ultraviolet absorbers and stabilizers. It has good heat resistance and cold resistance, good chemical stability, and can resist corrosion by acids, alkalis and organic solvents; it has relatively high rigidity and toughness, good mechanical strength, and good resistance to environmental stress cracking and tearing; it has excellent puncture resistance and can resist most plant root systems. It has a high anti-seepage coefficient, aging resistance, ultraviolet resistance and strong decomposition resistance, and can guarantee an eight-year service life for the anti-seepage membrane. It is also environmentally friendly and non-toxic. After several years of demonstration and promotion, we have continuously optimized and improved the construction process and farming technology, gradually standardizing and proceduralizing them, producing relatively good results, receiving an enthusiastic welcome from the vast number of farmers, and having broad development prospects.
Q: The anti-seepage film is black. In the heat of midsummer, the water temperature in the fish pond will certainly rise extremely fast. Even with the best shading treatment, the water temperature can easily reach or exceed the high-temperature limit for rice field eels. Won't the eels all die?
A: This inference is "completely wrong"! You may not know that rice field eels in still-water, soil-free ecological farming in membrane ponds live at the lowest layer of the pond. Although the outside air temperature reaches above 37°C, through three-dimensional ecological farming, we plant loofah, grapes and so on beside the pond to provide shade, and also plant vegetables on the water surface and transplant aquatic plants, which not only purifies the water quality but also provides shade. Therefore, generally at 15 cm below the water surface, the water temperature is only about 33°C, and in June, July and August of summer, when the water level is generally about 30 cm, the water temperature is even lower. So the water temperature at the bottom of the pond generally will not suddenly rise or fall sharply.
Q: You use apple snails and river snails in the membrane pond as an ecological chain link to maintain the natural balance of the ecosystem. As everyone knows, snails are intermediate hosts of many pathogens. Won't using them increase the incidence of disease in rice field eels?
A: Apple snails have a wide diet and can feed on leftover feed and accumulated feces from rice field eels, thus to a certain extent promptly purifying the water quality. We add 2 jin of apple snails or river snails per 20 sq m pond. While strictly sterilizing and disinfecting, we scientifically suppress the occurrence of rice field eel diseases by controlling the quantity, rather than arbitrarily putting apple snails or river snails into rice field eel ponds.
Q: I think everyone knows that the temperature difference inside and outside a greenhouse is very large. Fish ponds need water changes, and the water temperature of fish ponds inside the greenhouse is relatively high, while the water temperature outside is relatively low. With such a large temperature difference when water goes in and out, won't the rice field eels catch a cold?
A: There is a certain difference between the water temperature inside and outside the greenhouse, generally about 5°C. For ordinary water changes, we only need to replace one third of the pond water volume. Don't you all know about "seedling hardening"?