Metabolic-enhanced ecological recirculating aquaculture system and method suitable for relay culture of rice field eel

Abstract

The application relates to a metabolic reinforced ecological circulating water aquaculture system suitable for relay breeding of ricefield eels, wherein a breeding pond unit is a variable-width runway type breeding pond, the width ratio of the water inlet end to the water outlet end is 2:1-3:1, a plurality of eel nests are hung in the breeding pond, bait tables are arranged on each eel nest, and the bait tables are used for feeding ricefield eels; a water quality purification unit sequentially comprises a drum type solid-liquid separator, a moving bed type biological filter and a drip type biological filter in the water circulation direction, a pipeline at the water outlet end of the drip type biological filter is provided with an ultraviolet disinfection lamp; a temperature control unit comprises an air source heat pump and a refrigerating machine, and is communicated with the pipeline of the moving bed type biological filter to regulate and control the water temperature; an oxygenation unit is an air aeration oxygenation machine, and is communicated with the breeding pond unit and the moving bed biological filter; and a water circulation regulation unit is a circulating pump with a frequency converter, and is matched with a closed loop water circulation pipeline to adjust the hourly circulation times of the system water body.

Description

Technical Field

[0001] This invention relates to a system and method for farming eels, and more particularly to a metabolically enhanced ecological recirculating aquaculture system and method adapted for relay farming of eels, belonging to the field of aquaculture technology. Background Technology

[0002] With the continuous improvement of people's living standards, the market demand for eels has been increasing year by year. Traditional pond farming and rice paddy farming are constrained by factors such as season, region, and environment, making it difficult to meet the growing market demand in terms of both yield and quality. In particular, the problem of drug residues is serious in the later stages of farming. Currently, the pass rate of eel in major producing areas across the country is not high, mainly due to the problem of excessive levels of restricted drugs such as enrofloxacin and ciprofloxacin.

[0003] Enrofloxacin, ciprofloxacin, florfenicol, and other common fish medications are widely used for fish disease control due to their broad antibacterial spectrum and significant efficacy. However, excessive or improper use can easily lead to excessive drug residues in the fish, affecting product safety and human health. Improving the metabolic rate of fish and accelerating the metabolism and removal of these drugs in muscles and internal organs is crucial to ensuring the safety of aquatic food.

[0004] Drug metabolism in fish primarily relies on the hepatic microsomal enzyme system, the activity of which directly determines the efficiency of drug oxidation, reduction, and hydrolysis. In addition to strengthening nutritional regulation, improving the metabolic rate also requires optimizing the metabolic environment through aquaculture management.

[0005] First, proper water temperature control and maintaining a suitable growth temperature based on the characteristics of fish species can enhance enzyme activity. For example, maintaining a temperature of 25-30℃ or higher for warm-water fish can significantly accelerate drug conversion.

[0006] Secondly, ensuring sufficient dissolved oxygen and clean water quality is crucial. A high dissolved oxygen environment can enhance the metabolic level of fish, promote blood circulation, and accelerate the transport of drugs and their metabolites to excretory organs.

[0007] Third, we must manage toxic chemicals with high quality, regulate the concentrations of ammonia nitrogen and nitrite, avoid water quality deterioration that inhibits the body's metabolic function, and reduce the risk of drug residue accumulation.

[0008] To accelerate the metabolism of restricted drugs in fish and promote the removal of excessive drug residues, this invention develops an ecological recirculating water system and relay farming method to enhance the metabolic intensity of swamp eels, based on their biological characteristics and behavioral needs. It integrates three core methods: precise control of water temperature gradient, high-level and stable water quality assurance, and dynamic stimulation of variable-speed water flow, to construct an optimal growth environment adapted to the metabolism of fish. Summary of the Invention

[0009] The purpose of this invention is to enhance the metabolic intensity of eels through an ecological recirculating aquaculture system and a relay-style aquaculture method, providing an ecological and efficient solution for drug residue management. This ecological recirculating aquaculture system and relay-style aquaculture method integrates three core methods: precise control of water temperature gradient, stable high-level water quality, and dynamic stimulation of variable-speed water flow, constructing an optimal growth and metabolic environment suitable for fish metabolism. Water temperature gradient regulation activates the activity of liver metabolic enzymes, high-level water quality prevents metabolic function suppression, and variable-speed water flow stimulation enhances the body's circulation and metabolic rate. The synergistic effect of these three methods significantly enhances the fish's own metabolic intensity, efficiently accelerating the degradation and excretion of target drugs, providing an ecological and efficient solution for drug residue management in aquaculture, while ensuring both aquaculture safety and sustainability.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A metabolically enhanced ecological recirculating aquaculture system adapted for relay-style eel farming includes a breeding pond unit, a water purification unit, a temperature control unit, an aeration unit, a water circulation regulation unit, and piping components. Each unit is connected via piping components to form a closed-loop water circulation system. The breeding pond unit is a variable-width racetrack-type pond with an inlet-to-outlet width ratio of 2:1 to 3:1. Multiple sets of eel nests 2 are suspended within the pond, each set equipped with a feeding platform 1 for targeted feeding of the eels. The water purification unit operates along the water circulation path... The system comprises, in sequence, a rotary drum solid-liquid separator, a moving bed biological filter, and a trickling biological filter. The outlet pipe of the trickling biological filter is equipped with an ultraviolet disinfection lamp. The temperature control unit includes an air source heat pump and a chiller, which are connected to the moving bed biological filter to regulate the water temperature. The aeration unit is an air aerator, which is connected to the aquaculture pond unit and the moving bed biological filter. The water circulation control unit is a circulation pump with a frequency converter, which is adapted to the closed-loop water circulation pipeline and can adjust the hourly circulation frequency of the system water.

[0012] Preferably, the water inlet end is provided with a water distribution pipe 4; the water outlet end is provided with a U-shaped water outlet pipe 5.

[0013] Preferably, the metabolically enhanced ecological recirculating aquaculture system is located indoors, and the aquaculture ponds are in the shape of right-angled trapezoids, with a pair of aquaculture ponds in a complementary configuration and a walking passage in the middle.

[0014] Preferably, the multiple sets of eel nests 2 are arranged at the front and middle of the breeding pond along the water flow direction.

[0015] Preferably, it also includes a sludge collection tank, which is connected to the solid-liquid separator and the trickling filter.

[0016] A metabolically enhanced recirculating aquaculture system adapted for relay farming of swamp eels, employing any of the above-mentioned metabolically enhanced recirculating aquaculture systems, includes the following steps:

[0017] S1. Construct a metabolically enhanced ecological recirculating aquaculture system;

[0018] S2. Preparation before relay-type aquaculture: Before the eels are transferred to the pond ecological net cage for relay-type aquaculture, the ecological recirculating water system controls the initial water temperature of the aquaculture pond unit to ±0.5℃ of the highest value of the pond ecological net cage water temperature through an air source heat pump and a chiller. By adjusting the pH value of the moving bed biological filter, the pH value of the water in the aquaculture pond unit is adjusted to 7.0~7.5.

[0019] S3. Selection and stocking of loach: Select loach that have been cultured in pond ecological net cages from May to October, have not used prohibited substances, have been fed with a mixture of fish paste and commercial compound feed at a ratio of ≥3:1 for more than 3 weeks, have an individual size of ≥100g and a fatness of 0.09-0.13, and transfer them to the ecological recirculating aquaculture system within 6 hours after harvesting. The initial stocking density is 30-50kg / m³.

[0020] S4. Precise control of water temperature gradient during relay farming: After the eels are introduced into the pond, the water temperature of the farming system is raised by 0.5-1℃ every day, and after about 2 weeks it is raised to 30-32℃ and stabilized for 1 week. Then the water temperature is lowered by 0.5℃ every day until it reaches 25-27℃ and is then stabilized.

[0021] Meanwhile, during the relay farming period, feeding and nutritional control are as follows: animal-based fish paste and commercial compound feed are used as feed, with a ratio of 3:1 to 2:1. Feed once a day, with a daily feed amount of 1% to 3% of the eel's body weight.

[0022] Meanwhile, during the relay-style aquaculture period, dynamic stimulation of variable-speed water flow and water quality management are implemented: during normal times of the day, the hourly circulation frequency of the ecological recirculating aquaculture system is 0.08 to 0.2 times; 2 hours to 1 hour before the daily feeding of the eels, the hourly circulation frequency of the system is adjusted to 0.5 to 1 time; 0.25 to 1.25 hours after the eels finish feeding, the hourly circulation frequency of the system is adjusted to 0.5 to 1 time.

[0023] Preferably, in step S1, the ecological recirculating water system comprises an aquaculture pond, a rotary drum solid-liquid separator, a moving bed biological filter, a circulating pump, a trickling biological filter, an air source heat pump, a chiller, an ultraviolet disinfection lamp, an air aerator, a water distribution pipe, and inlet and outlet pipe fittings; wherein, the aquaculture pond is a variable-width racetrack type, with a length-to-width ratio of 2:1 to 8:1, and the ratio of the width at the inlet end to the width at the outlet end is 2:1 to 3:1, thereby increasing the flow velocity at the tail end of the aquaculture pond. The system features efficient water flow and wastewater discharge for the eels; a U-shaped outlet pipe with a grille at the water outlet; a 10-15cm rim around the breeding pond to prevent escape; and eel nests consisting of 5-7 stacked "S"-shaped grooved plastic panels suspended at the front and middle of the breeding pond, with a 15-30cm diameter hole in the center of each nest serving as a feeding platform for targeted feeding of the eels. Before being put into use, the ecological recirculating water system requires 20-30 days for the biofilm to mature.

[0024] Furthermore, in step S3, after harvesting from the pond ecological cages between May and October each year, the fish are disinfected by soaking in 3% to 5% saline solution for 5 to 10 minutes, and then transferred to the ecological recirculating water system for relay aquaculture within 6 hours of harvesting.

[0025] Furthermore, in step S4, feeding and nutritional regulation during relay farming: the fish paste consists of silver carp, small miscellaneous fish, earthworms, and red threadworms.

[0026] This invention ensures a favorable aquaculture environment for eels through the construction of an ecological recirculating water system. It integrates three core methods: precise control of water temperature gradients, stable high-level water quality, and dynamic stimulation of variable-speed water flow. This constructs an optimal growth and metabolic environment suitable for fish metabolism, with the following beneficial effects:

[0027] 1) A novel relay-style farming system and specific methods for eels are provided, which fundamentally solves the problem of drug residues in eels and improves the quality of the food.

[0028] 2) Under the premise of adapting to changes in the breeding mode by using gradient high temperature, a high success rate of relay breeding can be guaranteed.

[0029] 3) Stable, higher water temperature enhances metabolism and enzyme activity, significantly accelerating drug conversion.

[0030] 4) Feed the eels properly in a relay farming system to maintain their plumpness.

[0031] 5) Stimulating the eels with variable-speed water flow twice a day promotes their movement and accelerates their metabolism.

[0032] 6) The large water flow after feeding promotes the purification of aquaculture waste and ensures high-level water quality management.

[0033] 7) The breeding pond is a widened raceway type with a length-to-width ratio of 2:1 to 8:1. The ratio of the width of the inlet end to the width of the outlet end is 2:1 to 3:1, which improves the flow velocity at the tail end of the breeding pond, the flow pattern of the water body where the eels live, and the sewage discharge effect. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the metabolic enhancement ecological recirculating aquaculture system adapted to the relay farming of yellow eels in this invention.

[0035] Figure 2 yes Figure 1 A structural plan of the eel farming pond in the ecological recirculating aquaculture system.

[0036] In the picture, 1. Feeding platform, 2. Eel nest, 3. Pond wall and escape prevention edge, 4. Water distribution pipe, 5. U-shaped water outlet pipe. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0038] Eels are generally cultured in ponds and cages. Common fish drugs such as enrofloxacin, ciprofloxacin, and florfenicol are widely used for fish disease control due to their broad antibacterial spectrum and significant efficacy. However, excessive or improper use can easily lead to excessive drug residues in the body, affecting product safety and human health.

[0039] This invention aims to improve the metabolic rate of fish and accelerate the metabolism and removal of such drugs in muscles and viscera. To this end, it provides a metabolically enhanced recirculating aquaculture system adapted for relay-style eel farming, along with a corresponding farming method.

[0040] The breeding method includes the following steps:

[0041] 1) Structure of the ecological recirculating water system. The ecological recirculating water system consists of aquaculture ponds, rotary drum solid-liquid separators, moving bed biological filters, circulating pumps, trickling biological filters, air source heat pumps, chillers, ultraviolet disinfection lamps, air aeration and oxygenation machines, water distribution pipes, inlet and outlet pipe fittings, etc.

[0042] The breeding pond is a widened racetrack type, with a length-to-width ratio of 2:1 to 8:1. The ratio of the width at the inlet to the width at the outlet is 2:1 to 3:1, which improves the flow velocity at the tail end of the pond, the flow pattern of the water body where the eels live, and the sewage discharge effect. The outlet end has a grid and a U-shaped outlet pipe. The breeding pond is surrounded by a 10-15cm rim to prevent escape. At the front and middle sections of the breeding pond, there are eel nests made of 5-7 stacked "S"-shaped grooved plastic plates. In the center of each eel nest, there is a vertically extending hole with a diameter of 15-30cm, which serves as a feeding platform for targeted feeding of the eels. Before being put into use, the breeding system takes 20-30 days to mature and form a biofilm.

[0043] 2) Preparations before relay-style aquaculture. Before the eels are transferred to the pond ecological cages for relay-style aquaculture, the initial water temperature of the ecological recirculating water system is controlled to be ±0.5℃ of the highest value of the pond ecological cage water temperature, and the pH value is adjusted to 7.0~7.5.

[0044] 3) Selection and stocking of eels. Eels to be cultured in a relay aquaculture system should meet the requirements of this system. Specifically, they should have been cultured in ponds or ecological net cages, free from the use of prohibited substances, and fed a mixture of fish paste and commercial formulated feed at a ratio of ≥3:1 for at least 3 weeks before the relay aquaculture. Individual eels should be ≥100g in size and have a condition factor of 0.09–0.13. Harvesting should be carried out from ponds or ecological net cages between May and October each year. After harvesting, the eels should be disinfected by soaking in a 3%–5% saline solution for 5–10 minutes and transferred to the ecological recirculating aquaculture system within 6 hours of harvesting. The initial stocking density should be 30–50 kg / m². 3 .

[0045] Explanation of the concept of fatness: The general formula for calculating the fatness of fish in aquaculture is fatness (K) = weight (g) / body length³ (cm). This standard is also used for calculating the fatness of eels. The result is a pure numerical value with no unit or dimension.

[0046] 4) Precise temperature gradient control during relay-style aquaculture. After the eels are transferred to the ecological recirculating aquaculture system, the water temperature is increased by 0.5–1°C daily, reaching 30–32°C within approximately two weeks, and then stabilized for one week. Subsequently, the water temperature is decreased by 0.5°C daily until it reaches 25–27°C and remains stable. This gradual increase in temperature, adapting to the change in aquaculture mode, ensures a high success rate in relay-style aquaculture. The stable, higher water temperature enhances metabolism and enzyme activity, significantly accelerating drug conversion.

[0047] 5) Feeding and Nutritional Regulation During Relay Farming. After the eels are transferred to the ecological recirculating aquaculture system, a reasonable nutritional ratio should be maintained, mainly the ratio of animal-based feed (fish paste) to commercial compound feed, generally 3:1 to 2:1. The fish paste consists of silver carp, small miscellaneous fish, earthworms, and bloodworms. Eels should be fed once a day, with strict control over the amount. The daily feed intake should be 1% to 3% of the eel's body weight, and it should be consumed within 20 minutes. This focus on animal-based protein feed ensures the quality and health of the eels.

[0048] 6) Dynamic stimulation of variable-speed water flow and high-level water quality management during relay-style aquaculture. During normal times of the day, the hourly circulation frequency of the ecological recirculating aquaculture system is 0.08–0.2 times. Two hours before feeding the eels, the circulation flow is adjusted to increase the hourly circulation frequency to 0.5–1 times. Then, 0.25–1.25 hours after feeding, the circulation flow is adjusted again to increase the hourly circulation frequency to 0.5–1 times. This twice-daily stimulation of variable-speed water flow promotes eel movement and accelerates metabolism; the larger water flow after feeding promotes the purification of aquaculture waste and ensures high-level water quality management.

[0049] The following is a more specific example:

[0050] 1) Construct an ecological recirculating water system. This ecological recirculating water system includes four aquaculture ponds, each 3m². 2 The pond is 1m deep with a working water depth of 0.7m. It has 15cm beveled edges around the perimeter to prevent escape. It also includes one rotary drum solid-liquid separator with a maximum flow rate of 50m³ / h. 3 / h; Moving bed biofilter, 1m 3 Maximum flow rate 10m³ 3 / h; 2 circulating pumps, equipped with frequency converters to adjust the circulation flow rate, maximum 10m³ / h; 3 / h; Trickling biological filter 1m 3 Maximum flow rate 10m³ 3 / h; Air source heat pump, 15kW; Chiller, 3.5kW; Ultraviolet disinfection lamp, maximum 10m 3 The system consists of an air aerator (1.5kW), water distribution pipes, and inlet / outlet pipe fittings. The breeding pond is racetrack-shaped with a length-to-width ratio of 4:1 and a 2:1 width-to-outlet ratio. The outlet has a U-shaped grating. Three sets of eel nests, each consisting of 5-7 stacked "S"-shaped grooved plastic panels, are suspended at the front and middle of the pond. Each nest has a vertically extending hole (15-30cm in diameter) for targeted feeding of the eels. Before formal operation, the breeding system is filled with water and Bacillus subtilis preparation at a rate of 20g / m³ is added. 3 After 30 days of operation, the biofilm matures. The aquaculture system is placed in an indoor aquaculture workshop away from direct sunlight.

[0051] 2) Preparations before relay-style aquaculture. Before the eels are transferred to the ecological net cages in the ponds for relay-style aquaculture, the highest daily water temperature of the eel farming ponds is measured to be 26℃. The initial water temperature of the ecological recirculating water system is controlled at 26℃, the highest value of the water temperature in the ecological net cages, and the pH value is adjusted to about 7.2.

[0052] 3) During a week of consecutive sunny days in mid-June, select eels that have been cultured in ponds or ecological net cages, have not been given any prohibited substances, and have been fed a mixture of fish paste and commercial formulated feed at a ratio of 4:1 for 22 days. The eels should be approximately 120g in size and have a condition factor of approximately 0.11. After harvesting on sunny days, disinfect them by soaking them in a 5% saline solution for 8 minutes, and then transfer them to an ecological recirculating aquaculture system. The initial stocking density is approximately 35kg / m². 3 .

[0053] 4) After the eels are transferred to the ecological recirculating water system, the water temperature of the breeding system is increased by 0.5℃ every day until it reaches 30℃ and is stabilized for 1 week; then, the water temperature of the breeding system is decreased by 0.5℃ every day until it reaches 27℃ and is stabilized.

[0054] 5) After the eels are transferred to the ecological recirculating aquaculture system, the ratio of animal feed (fish paste) to commercial compound feed should be controlled at 3:1. The fish paste consists of silver carp and small miscellaneous fish. Eels should be fed once a day, and the amount of feed should be strictly controlled. The daily feed amount should be 2% of the eel's body weight, and it is advisable to finish eating within 20 minutes.

[0055] 6) Dynamic stimulation of variable-speed water flow and high-level water quality management during relay-style aquaculture. During normal times of the day, the hourly circulation frequency of the ecological recirculating aquaculture system is 0.08 times; from the 2nd hour to the 1st hour before feeding the eels each day, the circulation flow is adjusted to increase the hourly circulation frequency to 0.5 times; from 0.25 to 1.25 hours after the eels finish feeding, the circulation flow is adjusted to increase the hourly circulation frequency to 0.75 times.

[0056] In this case, the survival rate of the eels raised for 56 days was 91%, which meets the maximum residue limits for enrofloxacin, ciprofloxacin, and florfenicol in the national food safety standard "Maximum Residue Limits for Veterinary Drugs in Food" (GB 31650-2019) and its supplementary version (GB 31650.1-2022).

[0057] This invention solves the pain points of the prior art, significantly improves the metabolic rate of eels, accelerates the metabolism and removal of drugs in the muscles and internal organs of eels, and meets the requirements of the regulations.

[0058] The above are preferred embodiments of the present invention. Those skilled in the art can make various modifications or improvements based on these embodiments. Without departing from the overall concept of the present invention, such modifications or improvements should fall within the scope of protection claimed by the present invention.

Claims

1. A metabolically enhanced ecological recirculating aquaculture system adapted for relay farming of eels, characterized in that: It includes aquaculture pond units, water purification units, temperature control units, oxygenation units, water circulation control units, and pipe fittings. Each unit is connected through pipe fittings to form a closed-loop water circulation system. The breeding pond unit is a variable-width racetrack-type breeding pond with a water inlet width to water outlet width ratio of 2:1 to 3:

1. Multiple sets of eel nests (2) are suspended in the breeding pond, and each set of eel nests (2) is equipped with a feeding platform (1) for fixed-point feeding of eel feed. The water purification unit includes, in sequence along the water circulation direction, a rotary drum solid-liquid separator, a moving bed biological filter, and a trickling biological filter. The outlet pipe of the trickling biological filter is equipped with an ultraviolet disinfection lamp. The temperature control unit includes an air source heat pump and a chiller, which are connected to the pipeline of the moving bed biological filter to regulate the water temperature. The oxygenation unit is an air aerator, which is connected to the aquaculture pond unit and the moving bed biological filter. The water circulation control unit is a circulation pump with a frequency converter, which is compatible with the closed-loop water circulation pipeline and can adjust the number of hourly water circulations in the system.

2. The metabolically enhanced ecological recirculating aquaculture system adapted for relay farming of eels as described in claim 1, characterized in that: The water inlet is provided with a water distribution pipe (4); the water outlet is provided with a U-shaped water outlet pipe (5).

3. The metabolically enhanced ecological recirculating aquaculture system adapted for relay farming of eels as described in claim 1, characterized in that: The metabolically enhanced ecological recirculating aquaculture system is located indoors. The aquaculture ponds are in the shape of right-angled trapezoids, with a pair of ponds arranged in a complementary manner and a walking passage in the middle.

4. The metabolically enhanced ecological recirculating aquaculture system adapted for relay farming of eels as described in claim 1, characterized in that: The multiple sets of eel nests (2) are arranged in the front and middle parts of the breeding pond along the direction of water flow.

5. The metabolically enhanced ecological recirculating aquaculture system adapted for relay farming of eels as described in claim 1, characterized in that: It also includes a sludge collection tank, which is connected to the solid-liquid separator and the trickling filter.

6. A metabolically enhanced ecological recirculating aquaculture method adapted to relay-style eel farming, characterized by: The metabolically enhanced recirculating aquaculture system according to any one of claims 1-5 includes the following steps: S1. Construct a metabolically enhanced ecological recirculating aquaculture system; S2. Preparation before relay-type aquaculture: Before the eels are transferred to the pond ecological net cage for relay-type aquaculture, the ecological recirculating water system controls the initial water temperature of the aquaculture pond unit to ±0.5℃ of the highest value of the pond ecological net cage water temperature through an air source heat pump and a chiller. By adjusting the pH value of the moving bed biological filter, the pH value of the water in the aquaculture pond unit is adjusted to 7.0~7.

5. S3. Selection and stocking of loach: Select loach that have been cultured in pond ecological net cages from May to October, have not used prohibited substances, have been fed with a mixture of fish paste and commercial compound feed at a ratio of ≥3:1 for more than 3 weeks, have an individual size of ≥100g and a fatness of 0.09-0.13, and transfer them to the ecological recirculating aquaculture system within 6 hours after harvesting. The initial stocking density is 30-50kg / m³. S4. Precise control of water temperature gradient during relay farming: After the eels are introduced into the pond, the water temperature of the farming system is raised by 0.5-1℃ every day, and after about 2 weeks it is raised to 30-32℃ and stabilized for 1 week. Then the water temperature is lowered by 0.5℃ every day until it reaches 25-27℃ and is then stabilized. Meanwhile, during the relay farming period, feeding and nutritional control are as follows: animal-based fish paste and commercial compound feed are used as feed, with a ratio of 3:1 to 2:

1. Feed once a day, with a daily feed amount of 1% to 3% of the eel's body weight. Meanwhile, during the relay-style aquaculture period, dynamic stimulation of variable-speed water flow and water quality management are implemented: during normal times of the day, the hourly circulation frequency of the ecological recirculating aquaculture system is 0.08 to 0.2 times; 2 hours to 1 hour before the daily feeding of the eels, the hourly circulation frequency of the system is adjusted to 0.5 to 1 time; 0.25 to 1.25 hours after the eels finish feeding, the hourly circulation frequency of the system is adjusted to 0.5 to 1 time.

7. The metabolically enhanced ecological recirculating aquaculture method adapted for relay-style eel farming as described in claim 6, characterized in that: In step S1, the ecological recirculating water system consists of a breeding pond, a rotary drum solid-liquid separator, a moving bed biological filter, a circulating pump, a trickling biological filter, an air source heat pump, a chiller, an ultraviolet disinfection lamp, an air aerator, a water distribution pipe, and inlet and outlet pipe fittings. The breeding pond is a variable-width racetrack type with a length-to-width ratio of 2:1 to 8:1, and the ratio of the width at the inlet to the width at the outlet is 2:1 to 3:1, thereby increasing the flow velocity at the tail end of the breeding pond and stimulating the growth of eels. The system features a good balance between water flow and wastewater discharge; a U-shaped outlet pipe with a grille at the outlet; a 10-15cm rim around the breeding pond to prevent escape; and eel nests consisting of 5-7 stacked "S"-shaped grooved plastic panels suspended at the front and middle of the pond. Each nest has a vertically extending hole with a diameter of 15-30cm serving as a feeding platform for targeted feeding of the eels. Before being put into use, the ecological recirculating water system requires 20-30 days for the biofilm to mature.

8. The metabolically enhanced ecological recirculating aquaculture method adapted for relay farming of eels as described in claim 7, characterized in that: In step S3, after harvesting from pond ecological cages between May and October each year, the fish are disinfected by soaking in 3% to 5% saline solution for 5 to 10 minutes, and then transferred to the ecological recirculating water system for relay aquaculture within 6 hours of harvesting.

9. The metabolically enhanced ecological recirculating aquaculture method adapted for relay-style eel farming as described in claim 8, characterized in that: In step S4, feeding and nutrition regulation during relay farming: the fish paste consists of silver carp, small miscellaneous fish, earthworms, and red threadworms.

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