Questions and answers on controllable ecological culture of eel

Conventional intensive eel culture relies on a large number of water exchange and drugs to control diseases, which seriously restricts the survival and development of the eel industry. The technology of controllable ecological culture of eel can not only save water and energy, but also reduce the use of drugs or not. It is a feasible new technology of eel culture. □ / Yuan Chonggui National Aquatic Technology Promotion Station, School of Bioscience and Engineering, Fuzhou University. 1. What is the controllable ecological culture of eel? Answer: when people talk about "ecological farming", it will be understood as a simple, natural, extensive, low-yield, inefficient way of breeding. However, when the word "controllable" is added, the above understanding is completely wrong. Controllable ecological aquaculture is an intensive and efficient intensive farming model, which has the characteristics of "health and safety, economy and practicality, energy saving and emission reduction, high efficiency and environmental protection". "controllable ecological culture of eel" is a relatively complex ecological system engineering. Popularly speaking, it is through artificially and consciously changing the existing eel culture facilities to regulate and create a good ecological environment more suitable for the growth and development of eels as far as possible: using the principle of biological mutual inhibition to effectively prevent the occurrence of diseases and insect pests and reduce the use of drugs or no drugs. By controlling mild heat preservation to reduce the impact of climate change on eel culture, greatly shorten the growth cycle and improve feed efficiency; by reducing or even not changing water, saving a lot of energy and reducing production costs; through moderate light and oxygen to improve the vitality of the water ecosystem; through the physical treatment of eel feces to control the balance of biological digestion and maintain the self-purification ability of microecology. Through these measures, the water ecosystem can go beyond nature and efficiently produce healthy, safe and high-quality eels in accordance with our wishes. 2. Why should controllable ecological farming be kept warm? A: eel is an animal with variable temperature, and its growth and metabolic efficiency depend on the temperature of culture water. When the temperature is suitable (about 25 ℃ for European eel and 27 ℃ for Japanese eel), its metabolism is exuberant, the efficiency of digestion and absorption of food is the highest, and the growth rate is the fastest. If the temperature is too high or too low, the digestion and absorption of food by eels are affected, and the growth is relatively slow. In eel culture, the construction of greenhouse, the installation of heating and temperature control system to maintain the optimal growth temperature of eel is not only beneficial to the growth of eel, but also conducive to the reproduction of various plankton and bacteria, and maintain the balance of microecology in the water. At the same time, building a greenhouse can properly daylight to meet the growth needs of photosynthetic phytoplankton in the water, effectively consume nutrients in the water and purify water quality; the greenhouse also helps to reduce heat loss and keep the water temperature relatively constant, so that eel culture is basically not affected by season and climate change. 3. Why should the oxygenation system be installed in controllable ecological farming? Answer: different from traditional factory farming, there are a large number of zooplankton, phytoplankton and decomposing microorganisms in aquaculture water. In cloudy days and at night, especially in the latter part of the night, all organisms in the aquaculture water reduce or stop photosynthesis, while the oxygen consumption of relative respiration increases greatly, which may cause short-term hypoxia in the water body and pose a threat to the health of eel. This is the bottleneck problem of controllable ecological culture. If the dissolved oxygen in the water is not increased at this time, the floating head of eel is most likely to die due to hypoxia and the water quality deteriorates rapidly. Therefore, it is necessary to install oxygen-increasing facilities in the eel culture pond to add dissolved oxygen to the culture water in time, so as to break through the bottleneck of short-term hypoxia every day. By strengthening oxygen addition, the high digestibility of microorganisms in water can be effectively maintained, and the density of eel culture in water can be greatly increased, thus the relative high yield per unit area can be obtained and the production efficiency can be improved. 4. Why should controllable ecological aquaculture avoid changing a large amount of water? A: "changing water in large quantities" is almost a "patent" of intensive aquaculture in our country. Due to the high density of aquaculture, the water quality is easy to deteriorate, so we have to adopt the method of changing water in large quantities, often several times or even more than ten times the daily amount of water. Such a large change of water culture results in very few plankton and decomposing microorganisms in the water. As the saying goes, "when the water is clear, there is no fish". Fish live in a clear water environment for a long time, similar to human living in a desert without vegetation and wetlands. The living environment is very bad. There are many disadvantages of fish culture in clear water caused by large exchange of water, such as: A. the feces discharged by fish in the culture water can not be decomposed in time and accumulate in large quantities due to the lack of plankton and decomposing microorganisms; B. the dissolved oxygen in the water is consumed continuously due to the respiration of culture organisms and the lack of photosynthetic supplement, which can easily lead to the rapid reduction of dissolved oxygen in the water. C. harmful bacteria such as water mold and common parasites of eel (such as melon worm, ring worm, rotifer, etc.) are most likely to multiply in this monotonous clear water system ahead of photosynthetic plankton such as algae and zooplankton, which can easily cause explosive diseases of fish. D. frequent change of water in the process of culture is not only a waste of water resources, but also each change of new water is a new environment for fish, resulting in fish often in a state of conditional stress, seriously affecting their food intake and growth; E. a large amount of water change makes the culture water temperature not easy to be constant, which not only causes fish stress, but also increases heating energy consumption and production cost. F. pathogenic bacteria, viruses and parasites are often brought through water sources due to frequent change of water, which greatly increases the incidence of fish disease; G. fish do not have sense of security in clear water, so they are vulnerable to environmental stress, and their feeding efficiency will be greatly reduced as a result. If we count the disadvantages of large-scale water exchange, it is not difficult for us to understand why the controllable ecological culture model does not use a large number of water exchange. Controllable ecological culture is like the so-called "fish culture water first". The so-called "water culture" means to reduce or even not change water as much as possible in the process of culture. a large number of phytoplankton, zooplankton and decomposing microorganisms are deliberately cultivated in the culture water body, so that the water body forms a biodiversity ecosystem and allows various microorganisms to digest fish faeces and other harmful substances in the water body efficiently. Purifying water quality and creating a balanced and stable ecological environment for fish can effectively avoid all kinds of disadvantages caused by fish culture in clear water. 5. Why can't water disinfectants and other drugs be used in controllable ecological farming? Answer: one of the most important links of controllable ecological culture technology is to cultivate a large number of plankton, plants and decomposable microorganisms in the culture water body, and sometimes to add "probiotics" to the culture water body. Its purpose is to achieve self-purification of water quality through the water ecosystem, while inhibiting the outbreak of harmful bacteria and parasites, and protecting the safety of fish. If water disinfectants, antibiotics or insecticides are used in the breeding process, a large number of microorganisms will die, and the carefully established water ecosystem will be destroyed or even collapsed. When the ecosystem in the water is out of balance, the harmful bacteria and parasites in the water always multiply in large numbers, which leads to diseases and insect pests. Drug abuse will fall into a vicious circle of "medication-water-disease-medication". A variety of drug-induced diseases often occur in fish, which may lead to the risk of excessive drug residues in fish. Controllable ecological aquaculture requires a stable and diverse biological system, and the use of any drug may damage the system and even cause serious consequences. 6. Why does feed formula have an effect on controllable ecological breeding? A: there is a dynamic balance between the digestibility of microorganisms in a controllable ecological culture system and the discharge of fish faeces. Excessive discharge of faeces will cause microecological imbalance and adverse effects. Whether the feed formula is reasonable or not directly affects the digestion and absorption rate of feed and the content of nutrients in fish feces. Eel ingestion of feed with unreasonable nutrition formula for a long time will result in poor health, which will affect the digestion and absorption rate of feed, increase the burden of ecosystem, and reduce the resistance of fish to disease. In addition, if antibiotics are added to the eel feed, it will kill the beneficial bacteria in the intestinal tract of the eel and affect the digestion and absorption capacity of the eel. The selection of a good feed formula is beneficial to improve its digestion and absorption rate, and the addition of fermented soybean meal or other active fermentation products to the feed formula is very beneficial to the culture of eel intestinal beneficial flora and help eel digestion and absorption. 7. Why does controllable ecological farming need reasonable density? A: in a controllable ecological culture system, the feces produced by fish are mainly digested by microorganisms in the water in a timely manner, while the digestibility of fish faeces in the water ecosystem is limited, and the culture density is too high. the feces produced may exceed the digestible capacity of the ecosystem, the ecological balance will be broken, and the water quality will deteriorate. In order to avoid this situation, it is very important to control the proper culture density. Preliminary experiments show that the culture density of young eel is feasible under the condition of no water change, no sewage discharge and relatively constant temperature, and the stocking density of adult eel culture can reach 6-8kg/m2 under the condition of no water change and no sewage discharge. 8. How can the controllable ecological culture model achieve higher density culture? A: in the controllable ecological aquaculture model, the key to achieving higher density farming is how to break through the limit of faeces digestion in the water ecosystem, which is also the issue that readers are most concerned about. We know that the limit of microbial digestion can not be broken, and the only solution is to separate some fish faeces from the water by physical methods, so as to reduce the burden of microorganisms and achieve balance under artificial control. this is a key link of controllable ecological farming. There are many specific separation methods, such as particle filtration, constructed wetland filtration, cyclone foaming separation and so on. The higher the efficiency of artificial separation of fish feces, the higher the stocking density. -: guzhang::guzhang:-- eel rice is delicious.