Eel culture

Eel seedling stocking

Eel fry cultivation is the production process of cultivating more than 10g of eel fry. This stage needs to be cultivated by three different types of ponds, including primary pond, secondary pond and tertiary pond. Eel species are the basis of adult eel culture. The quantity and quality of eel species directly affect the quality of adult eel culture. Therefore, in order to develop eel production, we must first focus on the cultivation of eel fry.

In order to improve/increase the smooth progress of eel seedling cultivation, in addition to all the above preparations, the following production links need to be done well.

1、 Feeding density of eel seedlings

Due to different breeding methods, the stocking density of eel seedlings varies. Generally, the stocking density of water stop tank is 150~300g/㎡, and that of running water tank is 500~1000g/㎡. It grows faster and has a high survival rate in low-density stocking.

2、 Feeding time of eel seedlings

For eel farms with heating conditions or warm water supply, eel seedlings should be released as early as possible, so as to extend the feeding period and improve the yield and quality of eel species. Since eel larvae can only start feeding and growing when the water temperature is above 15 ℃, it is appropriate to breed eel larvae in Lutian Pond when the natural water temperature is above 13 ℃. In this way, after a short period of temporary cultivation to adapt to the environment, eel seedlings can be eaten and domesticated when the water temperature rises. Eel seedlings in Guangdong and Fujian are stocked around the beginning of March.

3、 Counting and Weighing of Eel Seedlings

In order to control the stocking density of eel seedlings, they must be counted during stocking to calculate the stocking weight, specification and mantissa of each primary pool. The specific method is: first, gently mix the eel seedlings in the cage, then take random samples for 2~4 times, weigh 50g each time, put them in the eel seedling salvage sea, count them with a small bowl or spoon, and then calculate the average specification. Calculate the tail number per kilogram of eel seedlings to get the average specification.

4、 Adaptation of Eel Seedlings to Environment

After long-distance transportation, the eel seedlings are in a fatigue state. In addition, the temperature difference between the seedling container and the pool water temperature is too large (especially in the heated incubation pool), so there needs to be a process of adaptation. The specific method is: place the eel seedling tank beside the pool, gradually drench the eel seedling tank with pool water, and wait until the eel seedling temperature is close to the pool water temperature (generally 5 ℃) And then put it into the cage that was placed in the pool in advance; If nylon bags are used for oxygen filled transportation, the nylon bags can be put into the pool together with the seedlings, and when the bag temperature is close to the pool water temperature, the bags can be removed to put the eel seedlings into the cage. Generally, eel seedlings are kept temporarily for 30 minutes to 1 hour (with oxygen increasing machine turned on). After normal activities, dead seedlings and dirt are removed, weighed and counted respectively, and put into each eel seedling cultivation pool.

5、 Eel seedling disinfection

Eel fry are delicate, easy to be scratched during harvesting, temporary rearing and transportation, and suffer from water mold infection and bacterial body damage. Therefore, disinfection must be carried out during stocking. The disinfection method is medicine bath, one is to use a container for medicine bath, the other is to sprinkle medicine bath in the whole pool.

1. Disinfection steps and methods: when using container medicine bath, it is usually carried out in a large water tank, so it is also called tank bath. The specific method is to first fill the tank with 300~400kg of clean water, then according to the proportion of drug consumption, dissolve it in a small amount of water before pouring it into the tank, and open the aerator for aeration, constantly stir the water to make the drug solution evenly distributed, then weigh about 5kg of eel seedlings and immerse them in the drug solution together for 10~15 minutes, then take out the eel seedlings for breeding. The whole pool is sprinkled with medicine bath in the evening. After the medicine is dissolved, it is directly sprinkled in the primary pool, and the aerator is opened to stir the water, so that the medicine solution is evenly distributed.

2. Disinfection drugs and concentration: commonly used drugs mainly include methylene blue and salt.

3. Disinfection time: the medicine bath in the container shall be carried out before the eel seedling goes to the pool; The whole pool was sprinkled and disinfected in the evening of the day after the eel seedlings came into the pool.

Open water stop aquaculture is the main aquaculture mode in China. The scale of eel farm should be 50 mu. The breeding facilities mainly include eel pond, water injection and drainage system and ancillary facilities. Rivers, lakes, reservoirs and groundwater are used as water sources. Generally, only 1/10-1/7 of the pool water is exchanged every day. It mainly depends on planktonic cyanobacteria and water tankers or aerators to increase oxygen to improve water quality. Its advantages are low cost of pool construction and low power consumption. The disadvantage is that the yield is low, generally only 1000-2000 kg per mu.

1. Breeding facilities

(1) Specification of eel pond

Eel pool can be divided into four types: primary pool, secondary pool, tertiary pool and adult pool. The proportion of these ponds in the eel farm is 2:8:15:75, that is, an eel farm with 50 mu of water. The first level pond is 1 mu, the second level pond is 4 mu, the third level pond is 7.5 mu, and the adult eel pond is 37.5 mu. The uses and specifications of these pools are as follows.

Primary pool: used for feeding training of eel seedlings, and raising eel seedlings to about 0.2g. The area is 50-60 square meters, the pool depth is 0.8-1.0 meters, and the water depth is 0.5-0.6 meters.

Secondary pool: feeding 0.2-2 g eel species. The area is 200-400 square meters, the pool depth is 1.2-1.5 meters, and the water depth is 0.8-1.0 meters.

Tertiary pool: eel species weighing 2-20g are raised. The area is 400-800 square meters, the pool depth is 1.4-1.5 meters, and the water depth is 1.0-1. 2 meters.

Adult eel pond: breed eels weighing about 20g into 150-200g edible eels. The area is 800-1200 square meters, the pool depth is 1.5-1.6 meters, and the water depth is 1.0-1.2 meters.

(2) Shape and structure of eel pond

The shape of eel ponds at all levels should be round or square with four corners cut off. According to the characteristics of eels that are easy to escape, difficult to catch and have high requirements for water quality, they must have the functions of anti escape, easy catch and convenient water injection and drainage in structure. There are three forms of pool wall: block stone, brick mortar masonry, cast-in-situ concrete and concrete precast slab splicing. The pool wall around is vertical and smooth. The wall is 0.8-1.6 meters high. The top of the wall is covered with a cover plate that extends 5-10 centimeters into the pool. The embankment surface should be 0.3-0.5 meters above the water surface. The bottom of the pool has two types, namely, the bottom of the pot and the bottom of the pool, which should be hard and watertight. The bottom shall be paved with 20 cm thick stone ballast. After raking and compacting, 5 cm thick yellow sand shall be paved to close the joints. The primary pool shall also be plastered with cement mortar to facilitate seedling harvesting. The pan bottom drainage is set at a lower place in the center of the pool bottom. The flat low pool bottom is inclined to the drainage outlet, and the water inlet is opposite to the drainage outlet. The water injection port is located on the top of the pool wall, 20-30cm higher than the high water level of the pool, and extends about 30cm into the pool; The drainage outlet is set opposite to the water injection outlet, and there are three gates outside; The road net gate is used to prevent escape. Stainless steel mesh or polyethylene screen silk mesh is used. Its mesh size is 1-1.5 mm for eel seedling pool, 1.5-2 mm for eel seed pool, and 2-4 mm for adult eel pool. The second gate or dark box is suspended at the bottom to press out the bottom sewage. The third gate acts as overflow to keep the water level of eel pond constant.

Eel ponds have high requirements for water quality. Not only the water injection and drainage systems of each pond are required to be separated, but also the water injection and drainage sources of the whole eel farm must be strictly separated. Otherwise, it will cause self pollution due to the death of eel feces and a large number of microcystis, leading to serious death of eels.

(3) Food shed

Eels like to feed in the shade. A food shed (including a food table, a food place and a shade shed) should be set up near the pool facing the sun and leeward. The food table is a 90 × 45 × 20 cm rectangular frame, with a nylon mesh at the bottom of the frame that can allow eels to be free; The food court is set at the bottom of the water below the food table, and the stone slag or spiral shell is laid on it, which shall be solid and flat; Set up a shade shed above the dining table.

(1) Eel breeding

Eel breeding is the process of raising white baby eels with a weight of 0.1-0.2 to young eels with a weight of 10-20 grams. In the second year, most of the eel species can develop edible eels (150-200 grams/tail). The cultivation of eel seedlings is generally divided into three stages. The stocking specifications and density of eel ponds at all levels are as follows: 0.1-0.2g eel seedlings per square meter in the first level pond 0.2-0.3kg; 0.3-1 kg of 0.3-2 g eel seedlings per square meter in the secondary pool; There are 2-20g eel species 0.5-2kg per square meter in the tertiary pool.

Selection of eel seedlings: good eel seedlings require wide head, blunt snout and neat specifications; Swimming is lively, with no trauma, and the body color is bright and jade white; The skin is plump, the body is healthy, and there is no pathogen. The specification is about 6000 tails per kilogram.

Rearing of eel seedlings: the time for releasing the seedlings is 3-4 months, and it is suitable for stocking when the water temperature is above 20 ℃. Before releasing the seedlings, the breeding pool and eel seedlings should be medically sterilized. The disinfection method of the breeding pool is the same as that of the domestic fry breeding pool. See Table 7-2 for the method of eel seedling disinfection. The stocking density shall be in accordance with the requirements of the primary pool.

Feeding training: Feeding training is the key technique for success or failure of eel farming, which takes about one month. In the week after the eel larvae are lowered into the pond, efforts should be made to shift the eel larvae from scattered feeding to centralized feeding. Generally, silkworms are used as bait from the evening, and the reared silkworms are scattered on the food table. They are fed 4-5 times a day, accounting for 20-40% of the total body weight of eel seedlings. At the same time, a 15W electric light is hung above the food table to guide the eel seedlings around the food table for centralized feeding. It is also possible to set up a tent above the food table to shade in the daytime, creating a dark environment, which can also induce eel seedlings to feed. A week later, if most of the eels are led to the feeding table to feed, it indicates that the training of concentrated feeding has been successful. Then gradually postpone the feeding time and completely change it to daytime. From the second week, the feeding amount of silkworms should be gradually reduced, and the meat mince of fresh feed such as mussel meat, pig spleen or fresh fish should be increased, 4 times a day. The daily feeding amount accounts for 10-15% of the total body weight of eel seedlings. After 15 days, gradually mix silkworms or minced meat with formula feed, and gradually increase the proportion of formula feed. After one month, all the eel larvae can be used as compound feed, and fed twice a day. The daily feeding amount accounts for 5-8% of the total body weight of the eel larvae. The compound feed should be fully mixed with water, and if possible, an appropriate amount of oil should be added. Feed the mixed feed immediately to prevent α - starch from cracking and affecting adhesion.

Hierarchical feeding: Eel fry are raised in different sizes every 20-30 days due to the difference in their ability to compete for food among individuals. They should stop feeding for one day before being raised separately. Because the eel seedlings are still small, the first few times of separate breeding can be fished under the food platform with close eyes, and the healthy seedlings that are first on the food platform will be separated first; Later, as the individual grows up, Guangdong fish sieve or different mesh mesh knot free net can be used for sorting. After sorting, use the medicine bath of Shiteling to separate feeding according to grades. The stocking specifications and density of nursery ponds at all levels are as described above. The daily dosage of formula feed after separate feeding of eel is 3-5% of the total weight of fish. When the eel seedlings are raised to the middle and late November, most of the individuals can grow to about 20g, which can be put into adult eel ponds for breeding as eel species.

Water quality regulation: cultivating and managing the water quality of eel pond is a reliable improvement/increase of eel production. The main measures are: ① Cultivate microcystis to increase dissolved oxygen in water. As the dissolved oxygen source in the eel pond water mainly depends on the photosynthesis of microcapsules in cyanobacteria, therefore, when the number of microcapsules in the pond water is small and the transparency is too large, the microcystis species should be taken from the nearby pond, put into the eel pond, and applied ammonium sulfate, 1.0-1.5 kg per mu, for 2-3 consecutive days, for intensive fattening, so that they can rapidly reproduce and grow. ② Master the color of water. The water in the pool should be dark green, and the transparency should be about 25cm. When the water color changes from strong 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 two consecutive days. When there are too many microcystis, the water color is too thick, and the transparency is less than 15cm, new water should be injected to increase the transparency to about 25cm. ③ Timely disinfestation. Zooplankton is the enemy of Microcystis, especially rotifer. In order to limit rotifer reproduction, a certain number of bighead carp can be raised in eel ponds, generally 10-20 2-year-old bighead carp can be raised per mu. If zooplankton still reproduce too fast, it can be sprinkled with crystal trichlorfon to make the water in the pool zero. 5-1ppm concentration. ④ Start water injection timely. 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 part of domestic fish breeding. At the same time, 1/10-1/7 of the water should be changed every day. When changing the water, the residual bait and feces in the pool should be discharged out of the pool.

(2) Adult eel culture

Adult eel culture is the production process of cultivating commercial eels weighing 150-200g from eels weighing more than 20g. At present, there are two forms of pond adult eel culture in China: exclusive culture and mixed culture.

Pond culture: It means to raise eels in the pond at a high density. Generally, the yield of the pond is more than 1000 kg per mu.

Breeding of eel seeds: Before breeding of eel seeds, the eel pool and eel seeds should be medically sterilized before being put into the eel pool for breeding. The stocking time is generally in the middle of March, the last ten days to the first ten days of April, when the water temperature is above 13 ℃. The stocking density is determined according to the yield index, eel pond conditions, eel species specifications and breeding technology. Generally, the stocking amount of more than 1000 kg per mu is about 20 grams of eel species, and 150-200 kg per mu; The specification is about 50g, and 300-400kg per mu. The stocking density of semi flowing water pond can accommodate 3-5 kilograms of eels weighing about 20 grams per square meter, and 10-15 kilograms per square meter of well equipped flowing water pond.

Feeding management: feeding management mainly includes feed feeding, rotating catch and release, water quality management, fish disease prevention and control, etc.

There are two kinds of feeds for eel culture: fresh feed and compound feed. The feeding method adopts the principle of "four fixations". Feed once every morning from 9:00 to 10:00, and the daily feed amount at 25 ℃. The compound feed is 2-5% of the total weight of the pond eel, and the fresh feed is 10-15%. When the water temperature is low in early spring or late autumn, or the water temperature exceeds 30 ℃, the daily feeding amount can be reduced as appropriate. It is generally required to finish the feed within 20 minutes after feeding. Eel mixture shall be stirred evenly and gently. Refer to Table 7-3 for water and oil mixing amount. Feed immediately after mixing.

In the process of feeding, the individual growth rate of the date eel in rotation is very different, so we must take measures such as stocking by stages, catching by stages, catching big and keeping small, catching big and making up small. Generally, the eel shall be graded and diluted once every other month or so to make the eel in the same pool have regular specifications and reasonable density. If some eel species released at the end of March have reached the market specification at the beginning of June, they can be caught again; After June, the water temperature rises, and the eel is eager to grow fast. The second fishing can be carried out in late July, and the eel species will be released immediately after the fishing; At the beginning of September, a considerable number of fish reached the market specifications and were caught for the third time; In the middle of November, pond clearing fishing will be carried out, and those that do not meet the market specifications will be reserved as eel species released in the spring of the next year. Stop feeding 1-2 days before graded dilution, and change the water in the pool. The original pool is used to lift water, so that eels can empty the food in their intestines and stomach, and then use a smooth fish sieve for sorting. The operation shall be careful to avoid damaging the fish body.

Water quality management measures can refer to the practices of seedling cultivation stage.

Pond mixed culture dates There are two ways of mixed culture of eel in the pond where four major fishes are raised: no eel feed and eel feed. The former is matched with 50-100 eels of 15-20g per mu. The eels feed on wild miscellaneous fishes and shrimps, small benthic animals and feed scraps in the fishpond. At the end of the year, 10-15kg edible eels weighing 150-200g can be caught; The latter is to carry out high-density mixed breeding, with 1000-2000 eels of 15-20 grams of eels per mu, and feed eels once a day. The feeding amount is 1-2% of the total weight of eels. Eel can also eat wild fish, shrimp and benthic animals in the pond. At the end of the year, 150-300kg of edible eels can be captured. These two mixed farming methods have been widely promoted in the Pearl River Delta of Guangdong Province, which has significantly improved the economic benefits of fish ponds.