CATDOLL : CATDOLL: What are the breeding habits of eels?

Eel, also known as white eel, white eel, river eel, eel, green eel, wind bun, Japanese eel. Eel refers to the general term for species under the order Anguilla. Also known as eel, it is a fish that looks like a long snake and has the basic characteristics of fish. In addition, eels have migratory characteristics similar to salmon. Eels are fish, similar to snakes, but without scales, and are generally found in the sea area where salt water and fresh water meet.

Living habits

Eels like to live in clean, unpolluted waters and are the purest aquatic creatures in the world. Eels grow in rivers on land and migrate to the ocean to spawn when they mature. They only lay eggs once in their lifetime and die after spawning. This lifestyle is opposite to the anadromous migration of salmon and is called catadroumous. Their life history is divided into 6 different developmental stages. In order to adapt to different environments, their body shape and color change greatly at different stages: Egg stage: Located in deep-sea spawning grounds.

Willow eel (leptocephalus): drifts long distances in the ocean with the ocean current. At this time, the body is flat and transparent, as thin as a willow leaf, which is easy to drift with the current. Glass eel: When approaching coastal waters, the body becomes streamlined to reduce resistance and escape from strong ocean currents. Elvers: When entering estuary waters, melanin begins to appear, which also becomes a source of catch for aquaculture eel fry. Yellow eel: During the growth period in the river, the belly of the fish is yellow. Silver eel: When mature, the body of the fish turns silvery white similar to deep-sea fish, and the eyes become larger and the pectoral fins widen to adapt to the migration to the deep sea to spawn. The sex of eels is determined by the acquired environment. When the population is small, the proportion of female fish will increase, and when the population is large, it will decrease. The overall proportion is conducive to the increase of the population. Eel fry cannot be cultivated by artificial breeding. This is mainly because eels have a very special life history that is difficult to simulate in an artificial environment. Japanese eels grow up in freshwater rivers and begin to migrate to the sea in the summer, that is, they swim from rivers to the ocean to lay eggs, which is the opposite of the upstream migration of trout and salmon, which swim from the ocean back to rivers to lay eggs. Its spawning ground is thousands of kilometers away in the deep sea between the Philippines and the Malay Islands. Scientists discovered this spawning ground mainly because they caught a lot of its newly hatched fry here. The fry of the eel is about 6 cm long and weighs 0.1 grams, but it has a narrow head and a tall, thin and transparent body like a leaf, so it is called "willow leaf fish". Its body fluids are almost the same as seawater, so it can drift long distances with the ocean current without much effort. It takes about half a year for it to drift from the spawning ground back to the Kuroshio current and then back to the coast of Taiwan. It begins to metamorphose into a thin and transparent eel one month before arriving at the shore, also known as "glass fish". Therefore, from December to January every year, fishermen will be busy using hand-forked nets to catch eels that are about to go upstream on the coast near the river mouth and sell them to farmers. After the farmers buy them back and release them, the eels slowly begin to show color, turning into yellow young eels and silver adult eels. Under natural conditions, the largest eel that can be caught is 45 cm and weighs 1,600 grams. Eels spawn and reproduce in the deep sea and grow up in freshwater environments. They are ferocious, greedy, active, dormant during the day and come out at night, have strong phototropism, like running water, and like warmth. Adult eels grow fast, have a round, cone-shaped appearance, and are black and thin. In recent years, they have been more artificially cultivated, and the meat is crisp. This fish is common all year round, but it is the most plump and delicious in summer and winter. Eels are rich in nutrition, delicious, less thorny and meaty, and have the effect of cooling and relieving summer heat, nourishing and strengthening the body. There is also the yellow eel, which belongs to the family Synbranchidae and is also a fish. It is also similar to a snake, has no scales, and has a yellow belly, hence the name yellow eel. Yellow eels live in mud caves in ponds or on the banks of freshwater rivers. They cannot survive without water, and when they are caught, they are covered in saliva. Yellow eels are not only a delicious delicacy with tender meat and delicious taste, but also have been known for their nourishing and medicinal effects since ancient times.

Farming technology

Open-air water-stopping aquaculture

Open-air water-stopping aquaculture is the main aquaculture method in my country. The scale of an eel farm is preferably 50 mu. The aquaculture facilities mainly include eel ponds, injection and drainage systems and ancillary facilities. Rivers, lakes, reservoirs and groundwater are used as water sources. Generally, only 1/10-1/7 of the pond water is exchanged every day. It mainly relies on floating blue algae and water wheels or aerators to increase oxygen to improve water quality. Its advantages are low pond construction costs and low power consumption. Its disadvantages are low production, generally only 1000-2000 kg per mu. 1. Aquaculture facilities (1) Eel pond specifications Eel ponds can be divided into four types: primary ponds, secondary ponds, tertiary ponds and adult eel ponds. The ratios of these ponds in an eel farm are 2:8:15:75, that is, for an eel farm with a water surface of 50 mu, the primary pond is 1 mu, the secondary pond is 4 mu, the tertiary pond is 7.5 mu, and the adult eel pond is 37.5 mu. The uses and specifications of these ponds are as follows. Level 1 pond: used for training eel fry to attract food and raise eel fry to about 0.2 grams. Area is 50-60 square meters, pond depth is 0.8-1.0 meters, water depth is 0.5-0.6 meters. Level 2 pond: used for raising eel species weighing 0.2-2 grams. Area is 200-400 square meters, pond depth is 1.2-1.5 meters, water depth is 0.8-1.0 meters. Level 3 pond: used for raising eel species weighing 2-20 grams. Area is 400-800 square meters, pond depth is 1.4-1.5 meters, water depth is 1.0-1.2 meters. Adult eel pond: used for raising eel species weighing about 20 grams into edible eels weighing 150-200 grams. Area is 800-1200 square meters, pond depth is 1.5-1.6 meters, water depth is 1.0-1.2 meters. (2) Shape and structure of eel ponds The shape of each level of eel pond is preferably a circle or square with the four corners cut off. According to the characteristics of eels being good at escaping, difficult to catch and requiring high water quality, the structure must have the functions of preventing escape, facilitating catch and facilitating water injection and drainage. The pool wall can be made of stone blocks, brick mortar, cast-in-place concrete and prefabricated concrete panels. The pool wall is vertical and smooth all around, with a wall height of 0.8-1.6 meters. The top of the wall is pressed with a cover plate, which extends 5-10 cm into the pool. The embankment surface should be 0.3-0.5 meters above the water surface. The pool bottom has two types: pot bottom shape and flat bottom shape, which should be hard and watertight. The bottom is paved with 20 cm thick slag, which is raked and compacted, and then paved with 5 cm yellow sand with tight seams. The first-level pool should also be smeared with cement mortar to facilitate seedling collection. The drainage center of the pot bottom shape is set at the lowest point in the center of the pool bottom, and the flat bottom of the low-profile pool is inclined toward the drainage outlet, with the water inlet and drainage outlet facing each other crosswise. The water inlet is located on the top of the pond wall, 20-30 cm above the highest water level of the pond, and extends about 30 cm into the pond. The drainage outlet is located opposite the water inlet, with three gates on the periphery. The first net gate is used to prevent escape, and is made of stainless steel mesh or polyethylene silk mesh. The mesh size is 1-1.5 mm for eel fry ponds, 1.5-2 mm for eel seed ponds, and 2-4 mm for adult eel ponds. The second plate gate or dark box has a suspended bottom to press out the bottom sewage. The third plate gate acts as an overflow to keep the water level of the eel pond constant. Eel ponds have very high requirements for water quality. Not only does each pond require separate injection and drainage systems, but the injection and drainage water sources of the entire eel farm must also be strictly separated. Otherwise, it will cause self-pollution due to eel feces and the death of a large number of Microcystis algae, leading to serious deaths of eels. (3) Feeding sheds Eels like to feed in the shade. Feeding sheds (including feeding tables, feeding areas and shade sheds) should be built on the sunny and leeward side of the pond. The feeding table is a rectangular frame of 90×45×20 cm. The bottom of the frame is covered with a nylon mesh with a mesh size that allows eels to pass freely. The feeding area is set up at the bottom of the water below the feeding table, and is covered with gravel or snail shells. It must be firm and flat. A shade shed is built above the feeding table. 2. Eel farming (1) Eel seed cultivation Eel seed cultivation is the process of raising white eels weighing 0.1-0.2 grams to small eels weighing 10-20 grams. In the second year, most eels can be raised to edible eels for sale (150-200 grams per tail). The cultivation of eel fry is generally divided into three levels. The stocking specifications and densities of each level of eel pond are as follows: the first level pond is stocked with 0.2-0.3 kg of eel fry weighing 0.1-0.2 grams per square meter; the second level pond is stocked with 0.3-1 kg of eel fry weighing 0.3-2 grams per square meter; the third level pond is stocked with 0.5-2 kg of eel fry weighing 2-20 grams per square meter. Selection of eel fry: High-quality eel fry require broad head and blunt snout, uniform size; active swimming, no body trauma, smooth jade white body color; plump skin, strong body, no pathogen parasites. The specification is about 6,000 per kilogram. Stocking of eel fry: The stocking time is March-April, and it is more suitable to stock when the water temperature is above 20℃. Before stocking, the breeding pond and eel fry should be disinfected with drugs. The disinfection method of the breeding pond is the same as that of the domestic fish fry breeding pond. The disinfection method of eel fry can be referred to Table 7-2. The stocking density is carried out according to the requirements of the first-level pond. Feeding training: Feeding training is the key technology for the success of eel farming, and it takes about one month of training. In the first week after the eel fry is put into the pond, efforts should be made to make the eel fry change from scattered feeding to concentrated feeding. Generally, starting from the evening, silk earthworms are used as bait, and the clean silk earthworms are scattered on the feeding table. Feed 4-5 times a day, and the daily feeding amount accounts for 20-40% of the total weight of the eel fry. At the same time, hang a 15W electric light above the feeding table to attract the eel fry to the feeding table and feed them in a concentrated manner. You can also build a tent above the feeding table during the day to provide shade and create a dark environment, which can also induce the eel fry to feed. If most of the eel fry are attracted to the feeding table to feed after a week, it means that the concentrated feeding training has been successful. Then gradually postpone the feeding time, and finally change it to daytime. Starting from the second week, the amount of silkworms fed should be gradually reduced, and the minced meat of fresh feed such as clam meat, pig spleen or fresh fish should be increased. Feed it 4 times a day, and the daily feeding amount accounts for 10-15% of the total weight of the eel fry. After 15 days, gradually mix silkworms or minced meat with compound feed and feed it, and gradually increase the proportion of compound feed. After 1 month, you can switch to using all eel fry compound feed, feed it twice a day, and the daily feeding amount accounts for 5-8% of the total weight of the eel fry. The compound feed should be fully kneaded with water, and if conditions permit, add an appropriate amount of oil. Feed should be fed immediately after mixing to prevent α-starch from cracking and affecting adhesion. Grading feeding: During feeding, eel fry have different individual competition abilities, resulting in large differences in individual size. Therefore, eel fry of different sizes should be separated every 20-30 days, and they should be stopped from feeding for one day before separation. Because eel fry are still small, they can be caught under the feeding table with a fine-eye scoop for the first few times of separation, and the strong fry that first come to the feeding table will be separated first; later, as the individuals grow up, they can be sorted with Guangdong fish sieves or knotless nets of different mesh sizes. After sorting, they can be bathed in sulfamethoxazole and then raised according to grades. The stocking specifications and density of seedling ponds of each level are as described above. After eel fry are separated, the daily amount of compound feed is 3-5% of the total weight of the fish. When eel fry are raised to mid-to-late November, most individuals can grow to about 20 grams and can be put into adult eel ponds as eel species. Water quality regulation: Cultivating and managing the water quality of eel ponds is a reliable guarantee for high eel production. The main measures are: ① Cultivate Microcystis to increase dissolved oxygen in the water. Since the source of dissolved oxygen in the eel pond water mainly depends on the microcystis in the cyanobacteria produced by photosynthesis, when the number of microcystis in the pond water is small and the transparency is too large, the Microcystis species should be fished out from nearby ponds and put into the eel pond, and ammonium sulfate should be applied at 1.0-1.5 kg per mu for 2-3 consecutive days to carry out intensive fertilization to make it reproduce and grow rapidly. ② Master the water color. The pond water should maintain a dark green palladium, and the transparency should be about 25 cm. When the water color changes from dark green to light green or light yellow, or the transparency is greater than 25 cm, ammonium sulfate should be applied in time, 0.5-1 kg per mu for 2 consecutive days. When there are too many Microcystis, the water color is too dark, and the transparency is less than 15 cm, new water should be injected to increase the transparency to about 25 cm. ③ Timely deworming. Zooplankton is the biggest enemy of Microcystis, especially rotifers, which have the greatest impact. To limit the reproduction of rotifers, a certain number of bighead carps can be raised in the eel pond. Generally, 10-20 two-year-old bighead carps can be raised per mu. If the zooplankton still reproduces too fast, crystal dichlorvos can be sprayed to make the pond water concentration 0.5-1ppm. ④ Start the water injection at the right time. In order to improve the water quality of the eel pond, a waterwheel-type aerator should also be installed for oxygenation. The start-up time can refer to the domestic fish farming section. At the same time, 1/10-1/7 of the water should be changed every day. When changing the water, the remaining bait and feces in the pond water should be discharged out of the pond. (2) Adult eel farming Adult eel farming is the production process of raising eels weighing more than 20 grams into commercial eels weighing 150-200 grams. At present, there are two forms of pond adult eel farming in my country: specialized farming and mixed farming. Special pond farming: that is, raising eels alone at a high density in the pond. Generally, the yield per mu of open-air ponds is more than 1,000 kilograms. Stocking of eel seeds: Before stocking eel seeds, the eel pond and eel seeds should be disinfected with drugs, and then they can be put into the eel pond for breeding. The stocking time is generally from mid-to-late March to early April, when the water temperature is above 13℃. The stocking density is determined by factors such as production indicators, eel pond conditions, eel seed specifications and breeding technology. Generally, the stocking amount for an acreage yield of more than 1,000 kg is 150-200 kg for eel seeds of about 20 grams per acre; 300-400 kg for eel seeds of about 50 grams per acre. The stocking density of semi-flowing ponds is 3-5 kg ​​of eel seeds weighing about 20 grams per square meter, and 10-15 kg per square meter for well-equipped flowing ponds. Feeding and management: Feeding and management work mainly includes feeding, rotation of fishing and stocking, water quality management, fish disease prevention and control, etc. Feeding and feeding There are two types of eel feeds: fresh feed and compound feed. The feeding method adopts the four-determination principle. Feed once a day at 9-10 am. When the water temperature is 25℃, the daily feed amount is 2-5% of the total weight of the eels in the pond, and the fresh feed is 10-15%. When the water temperature is low in early spring or late autumn, or when the water temperature exceeds 30℃, the daily feed amount can be reduced as appropriate. Generally, the eel feed is required to be eaten within 20 minutes after it is thrown. The eel feed should be stirred evenly and gently. The amount of water and oil mixed can be referred to Table 7-3. Feed immediately after stirring. During the breeding process of the round-caught and round-released date eels, the growth rate of individuals varies greatly. It is necessary to adopt measures such as staged stocking, staged fishing, catching the big and leaving the small, and catching the big to supplement the small. Generally, the eels in the same pond are graded and thinned every month or so to make sure that the size of the eels is uniform and the density is reasonable. Some of the eels released at the end of March have reached the market size in early June, so the first catch can be carried out; after June, the water temperature rises, the eels are eager to eat and grow fast, and the second catch can be carried out in late July. After the catch, the eels are immediately restocked; in early September, a considerable number of eels reach the market size, so the third catch is carried out; in mid-November, the pond is cleaned and fished, and those that do not reach the market size are reserved for the next spring release. Feeding should be stopped 1-2 days before grading and thinning, and the pond water should be replaced. The original pond water should be suspended to empty the food in the stomach and intestines of the eels, and then they are sorted with smooth fish sieves. The operation should be careful and meticulous to prevent damage to the fish body. Water quality management: The water quality management measures can refer to the practices in the seedling cultivation stage. Pond polyculture: There are two ways to polyculture eels in the fish ponds that breed the four major carps: no eel feed and eel feed. The former is to use 50-100 eels weighing 15-20 grams per mu. The eels feed on wild fish and shrimp, small benthic animals and feed debris in the fish pond. At the end of the year, 10-15 kg of edible eels weighing 150-200 grams can be caught. The latter is to carry out high-density mixed breeding, with 1000-2000 eels weighing 15-20 grams per mu. Eel feed is fed once a day, and the feeding amount is 1-2% of the total weight of the eels. Eels can also eat wild fish and shrimp and benthic animals in the pond. At the end of the year, 150-300 kg of edible eels can be caught. Both of these mixed breeding methods have been widely promoted in the Pearl River Delta of Guangdong, which has significantly improved the economic benefits of fish ponds.

Pay attention to water quality management in hot season

"Water" is the lifeblood of the eel industry. Good water quality management is the top priority of aquaculture work in high temperature seasons. 1. Artificial cooling method. To lower the water temperature, you don't need "air conditioning" or "electric fans". You can also use artificial methods to lower the water temperature. The method is: 1. Cover the top of the intensive breeding pond with a layer of black sunshade cloth. The sunshade cloth can be ventilated and breathable, and can block direct sunlight, adding coolness to the water surface. In this way, the water temperature can be reduced by about 1℃~2℃. 2. Drain and change water in advance. Normally, drain and change water at 8 am. In the hot season, it can be advanced to 6 am, because the water body at night is relatively cooler than during the day. When the water temperature is low, drain and change water. This can also achieve the purpose of lowering the water temperature. 3. Raise the water level. In the hot season, whether it is an earthen pond or an intensive breeding pond, the water level should be raised to the highest limit. A high water level, a large water body space, and a slow temperature rise are also good ways to cool down. 4. Increase the amount of water change. When the temperature is highest at noon, use a machine well or deep well to add some cool water to the pool, which can also significantly reduce the temperature. 2. Flood exclusion method. The high temperature season is also a season of frequent heavy rains. Eel farms often suffer from eel poisoning, insect pests, gill rot and many other diseases due to floods entering the pool. How to avoid floods entering the pool: 1. Whenever there is a heavy rain, do not feed, discharge sewage, or change water. It is better to feed less than to risk using floods. 2. What should I do if a small amount of flood water enters the pool? Once a small amount of flood water enters the pool, use potassium permanganate 1.5ppm to adjust the water quality, or use quicklime 15-20ppm to improve the water quality, or use water purifier 3ppm to purify the water quality. 3. Adjust the time of sewage discharge and water change to avoid direct contact with floods. During floods, sewage discharge and water change can sometimes be carried out in advance, and sewage discharge and water change can sometimes be postponed. It is not subject to conventional restrictions and floods should be avoided as much as possible. 4. What should I do if a large amount of flood water enters the pool? Once a large amount of flood water enters the pond, the first thing to do is to stop feeding, then use a water quality improver such as Haizhongbao for purification, and finally use potassium permanganate 2 ppm + insecticide 2# for insecticide removal, sterilization and disinfection.

Greenhouse water-stopping culture

This breeding method is matched with open-air ponds. A steel frame is built above the breeding pond, covered with plastic tiles or films, and heating measures are taken to keep the pond water at around 25°C. The specifications and stocking density of eel ponds at all levels and the feeding and management methods are basically the same as those of open-air pond breeding. The eel fry can be divided into ponds after about one month of breeding, and the survival rate is about 80%. The eel fry released in late February can be raised for 120-150 days and can grow into 3-5 grams of eel seeds. By the end of the year, they can grow into eel seeds of about 50 grams, and 20-30% of the eel seeds can be grown into edible eels for the market.

Eel disease prevention and control

Special attention should be paid to the prevention and treatment of fish diseases in eel farming. The main diseases include Saprolegniasis, Ichthyophthirius, Trichodinasis, Anchorhead disease, Gill rot, Eel bladder nematode disease and Red fin disease, which can be prevented and treated by conventional methods.

Earthen pond aquaculture technology

Eel, also known as white eel and white loach, is a precious fish for freshwater farming. Its meat is tender, delicious, and has high nutritional value. It has medicinal effects such as removing blood stasis, promoting new growth, and nourishing and conditioning. Eels grow rapidly and have strong adaptability. They can live normally even in waters with little dissolved oxygen and where other fish cannot live. Artificial breeding technology does not require high standards, and the source of feed is also wide. In recent years, farmers have been breeding eels in large quantities in earthen ponds, all of which have achieved high yields and high efficiency. Eel seeds are released in early spring and can be put on the market in late autumn and early winter, with an average yield of 800 to 1,000 kilograms per mu. The tips for high-yield and high-efficiency breeding of eels in earthen ponds are introduced as follows: 1. Pond selection and disinfection The earthen pond for breeding eels requires ventilation and sunshine, sufficient water sources, and the area should not be too large. Water lilies or water peanuts with a width of 0.8 to 1 meter are planted around the earthen pond, and fenced with fences or mesh, which can prevent eels from escaping and provide shade, which is conducive to their growth. Before stocking, the excessive silt in the land should be removed, the pond bottom should be leveled, the pond bank and the inlet and outlet should be repaired, and 10 to 15 days before the eel seeds are put into the pond, 100 to 125 kg of quicklime should be used for cleaning and disinfection per 1,000 square meters to completely kill wild fish and harmful organisms. Then, 5 to 7 days before the eel seeds are put into the pond, water should be filled to a depth of 0.6 to 0.7 meters, and the water inlet should be filtered with a 60-mesh sieve. Finally, basal fertilizer should be applied, generally 300 to 400 kg of decomposed pig and cow manure should be poured per 1,000 square meters, and the eel seeds should be put into the pond after the water turns light green or yellow-brown, so that they can eat sufficient natural bait after being put into the pond. The pond water will be deepened to 1.5 meters in about 15 days. 2. Eel seed processing and stocking The suitable temperature for eel growth is 20℃ to 28℃, and it starts to feed when the water temperature is 12℃, so the stocking time is generally from late February to mid-March. Before release, soak the eel packaging bag in water for 20 to 30 minutes to adapt to the water temperature. The bag can be opened only when the temperature difference between the inside and outside of the bag is less than 5°C. Then use a small basin to pour 2 to 3 basins of pond water into the bag to gradually adapt the eel species from a high dissolved oxygen state to a low dissolved oxygen state. At the same time, the eel species should be disinfected before release. Use 0.75 kg to 1 kg of salt to soak the eel species for 15 to 20 minutes for every 50 kg of water. The eel species released are required to have a grayish-blue body color, plump and elastic skin, and active swimming. The specifications of the eels in the same pond should be uniform, otherwise the competition between eels will affect the feeding of the weak individuals. The stocking density is generally 4,000 to 5,000 eels weighing about 20 grams per 1,000 square meters; 3,000 to 4,000 eels weighing about 50 grams can be released; and 2,000 to 3,000 eels weighing about 100 grams can be released. At the same time, 50 bighead carps, 30 silver carps, and 200 tilapia can be mixed in every 1,000 square meters of earth pond. On the one hand, they can filter plankton and clean the feces excreted by eels, which plays a role in purifying water quality; on the other hand, they can increase fish production. 3. Feed types and feeding Artificial breeding of eels mainly relies on special compound feed (available on the market), and 50 grams to 60 grams of multivitamins (vitamins A, B, C, E) and 1.5 kilograms to 2 kilograms of cod liver oil are added to every 50 kilograms of special feed (cod liver oil should be stopped when the water temperature is below 20℃ or above 35℃). Add less for young eels and more for adult eels. If there is a temporary lack of special feed, small fish, livestock and poultry viscera, silkworm pupae and other animal feeds can be minced and mixed with flour as a substitute, and the crude protein content must be above 40%. Eels are carnivorous fish and greedy. When feeding, the "four determination" principles should be implemented, namely, quality determination, quantity determination, timing, and location determination. Quality determination: that is, ensuring the quality of the feed. The prepared feed should be moderately hard and soft (the amount of water added is 1.2 to 1.3 times), fresh and clean, and should not deteriorate or rot. Quantification: that is, the amount of feeding should be appropriately fed according to the size, feeding, digestion, weather, water temperature, and water quality of the eels. The general daily feeding amount is 1.5% to 2.5% of the eel's body weight, and it is best to eat it within 12 hours. Timing: that is, if the fish size is small and the density is large, feed once at 8 am and 4 pm every day; if the eel size is more than 100 grams, feed once at 8 am to 9 am every day. Positioning: that is, feed is placed on a fixed feeding table, and 2 to 3 feeding tables can be set up for every 1,000 square meters of earthen pond. 4. Daily management and disease prevention Patrol the pond every morning and evening to observe the eel's activities and feeding conditions, and check the drainage outlet after rain to prevent fish from escaping. Add new water once every 10 to 15 days in normal times, and once every 5 to 7 days in summer and autumn, and the amount of water changed each time is about 10% of the entire pond. At the same time, pay attention to keep the pH value between 7 and 8.5. If the pH value is too high, new water should be added. If it is too low, use 15 kg to 20 kg of quicklime per 1,000 square meters to adjust it.

Warm water aquaculture

Eel farming in warm running water is currently the most advanced farming method. It requires that the water temperature be controlled at the most suitable water temperature for eels (around 27°C) and that running water farming be carried out. Its advantages are that eels have few diseases, grow fast, and have high yields. Generally, the eels are released in early February, and all of them can be grown into edible eels in the same year, with an output of about 15,000 kg per mu. The disadvantages are that the infrastructure investment is large and the farming is highly technical. This farming method can be divided into two types according to different water sources: factory waste heat warm drainage farming and indoor circulating filtration farming. The former uses factory waste heat warm drainage, which can save energy, has a simpler structure, and has a lower farming cost; the latter uses boilers for heating, and the pool water is recycled, and a biological filtration pool needs to be built, which has a more complex structure and a larger one-time investment. Eel farming in waste heat warm running water requires that the terrain elevation be used as much as possible to build eel pools so that they can be filled and drained automatically. Since the pool water is immediately discharged outside the site after use, it is generally operated in the open air. Its main facilities include: cold water and hot water pipes, temperature regulating pools, eel pools, and drainage pipes. Circulating filtration eel farms are generally operated indoors and equipped with biological filtration pools. The scale of warm water eel farms is generally 1-2 mu. Each pool is made of cement, with an area of ​​30-50 square meters, a depth of 1.2-1.4 meters, and a water storage of 1.0-1.2 meters. The pool is round or square with four corners cut off. The bottom of the round pool is in the shape of a pot bottom. The drain is located in the center of the pool bottom and consists of two semicircular drainage piers and three gates on both sides of the pier. The bottom of the square pool is flat and tilted towards the drain. Other equipment requirements and feeding management methods are roughly the same as those of open-air pools.

Eel, also known as white eel, white loach, etc., is a precious fish for freshwater farming. The eel has a slender body, cylindrical in the front and flat in the back. The body length is 16.0-20.7 times the body height and 6.9-7.8 times the head length; the head length is 4.4-5.5 times the snout length, 10.7-13.7 times the eye diameter, and 4.8-6.0 times the distance between the eyes. The eyes are small, the snout is protruding, and there is a longitudinal tooth belt on the upper jaw. The gill openings are well developed, there are two pectoral fins, no pelvic fins, the dorsal fin and anal fin are low and long, and the anal fin is connected to the caudal fin. The back is dark brown, the abdomen is white and spotless, the body surface is mucous, and the scales are mat-like and buried under the skin.

Characteristics of eels

Eels mainly feed at night. Adults mainly feed on animal baits, while young eels mainly feed on zooplankton, aquatic insects and organic debris. Young eels weighing about 5 grams begin to prey on fry. Small eels weighing 100 grams can chase small fish and shrimps. Eels feed in water temperatures above 12°C, that is, between March and November, with the highest intensity between June and July and September and October.

Eel is a river-dwelling fish. In spring, eel fry migrate near the river mouth to feed. The white eel is about 6 cm long and weighs 0.1 gram. After growing in fresh water for one year, it can grow to 15 cm long and weigh about 5 grams in the spring of the following year. In the spring of the third year, it can grow to 15 cm long and weigh about 15 grams. In the fourth year, it can grow to more than 50 grams. Under natural conditions, the largest eel that can be caught is 45 cm long and weighs 1,600 grams.

Eels lay eggs and reproduce in the deep sea, and grow up in freshwater. They are ferocious, gluttonous, active, and nocturnal. They are phototactic, like flowing water, like warmth, and live in caves. They have strong ability to swim upstream and can escape into caves. Every autumn, sexually mature eels go to sea to lay eggs and cum. The fertilized eggs hatch in the deep sea and develop to metamorphosis. When spring comes, they gather in groups from the sea mouth to live in fresh water.