Ctenopharyngodon idellus circulating water fasting quality repairing and conditioning method

Abstract

The invention discloses a grass carp circulating water fasting quality repairing and conditioning method, and belongs to the technical field of aquatic products. According to the method, fasting temporary rearing and hydrogen-rich water rearing are combined, and the grass carp meat quality is systematically improved. The method comprises the steps that commercial grass carps are placed in an outer pond for fasting temporary rearing for 5-7 months and then transferred into a hydrogen-rich water circulation system for fasting temporary rearing for 55-65 days, and during the fasting temporary rearing period of the hydrogen-rich water circulation system, the salinity of the water body is adjusted to be 0.4%-0.5%, the hydrogen-rich concentration in the culture water body is 0.05-0.1 ppm, the temperature is set to be 20-23 DEG C, the dissolved oxygen is 8.0 mg / L or above, and the pH is about 8.0. According to the method disclosed by the invention, nutritional ingredients of grass carp muscles are dynamically optimized, essential amino acids and flavor amino acids are increased, and the grass carp meat quality is effectively improved. In addition, the polyunsaturated fatty acid content of the grass carp obtained by the method is remarkably increased, the cooking sensory score of the grass carp is remarkably improved, the peculiar smell and fishy smell are remarkably reduced, and the compactness and chewiness of grass carp meat are remarkably improved through texture analysis.

Description

Technical Field

[0001] This invention patent belongs to the field of aquaculture and food processing technology, specifically relating to a method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system. Background Technology

[0002] In modern aquaculture, high-density farming and the use of high-fat feed lead to eutrophication of the aquaculture water and excessive fat accumulation in farmed fish. This situation further results in a decline in the quality and flavor of aquatic products, an increased fishy smell, and excessive fat accumulation. It also negatively impacts the nutritional composition of fish muscle, visceral fat content, body color, flavor, and health, thus affecting market acceptance. Ultimately, this leads to problems such as increased production without increased income and high yield without high efficiency in the aquaculture industry, seriously hindering the green, high-quality, healthy, and sustainable development of the aquaculture industry. To improve fish flavor and quality, the industry commonly adopts a method of temporary holding without feeding. This method involves transferring farmed fish to a clean water environment and holding them for a period of time without feeding or with very little feeding. During this period, the fish naturally eliminate excess fat, feces, and drug residues through metabolism, while the flowing water stimulates the fish to swim, further accelerating the metabolism of fat and odor-causing substances in their bodies.

[0003] However, existing fasting-based temporary holding models and systems have significant drawbacks. Prolonged starvation can easily lead to weakened fish immunity, triggering disease outbreaks and even causing large-scale mortality, making it difficult to guarantee the profitability of fish farmers. Furthermore, current industrialized aquaculture still largely relies on manual management and experience-based judgment, with low levels of automation. It cannot precisely control various parameters in the holding environment, such as water pH, dissolved oxygen levels, temperature, and water flow rate, resulting in low holding efficiency and poor fish quality improvement. In addition, some temporary holding systems suffer from large water exchange volumes, high energy consumption, and significant environmental pollution, failing to meet the requirements of sustainable development.

[0004] CN202111591219.X provides a hydrogen-rich water aquaculture device that introduces a mixture of hydrogen and oxygen into the water to improve the weight loss of aquatic animals. However, the cost is high, the system operation is cumbersome, and the improvement in aquatic product quality is relatively low. CN202120586706.6's core design involves producing hydrogen-rich water through a fish tank hydrogenation device for recycling; however, its applicability is limited and it cannot be used for large-scale aquaculture. Summary of the Invention

[0005] To address the problems of fat deposition, strong odor, and low survival rates in existing traditional aquaculture and temporary holding models, this invention provides a method for the quality restoration and conditioning of grass carp in a recirculating aquaculture system. This method offers a systematic solution to the aforementioned bottlenecks in the background technology, providing a technical foundation for promoting the application of grass carp and other aquatic products in functional foods and aquaculture.

[0006] The technical solution of the present invention is as follows: This invention first provides a method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system, which includes the following steps: S1. Commercial grass carp are transported to breeding ponds and temporarily kept for 5-7 months without any artificial feeding. S2. Construct a hydrogen-rich water circulation fasting temporary rearing system, the system including at least a rearing tank, an aerator, a hydrogen generator, an external circulation system, a temperature control system, and a water quality monitoring device; wherein, the external circulation system includes an external circulation pipeline, a circulating water pump installed in the pipeline, a protein separator, a physical filtration device, and a biological treatment tank; before the grass carp are transferred into the rearing tank, water is circulated in the rearing tank and the aerator is turned on for aeration, and salt is added after the water intake is completed to control the salinity of the water; S3. After temporary rearing in S1, the grass carp are transferred to the rearing tanks treated in S2 for temporary rearing in hydrogen-rich water circulation without feeding. During the temporary rearing period, the hydrogen generator and aerator operate in conjunction, and the circulating water pump runs continuously throughout the process. The hydrogen concentration in the water in the rearing tank is controlled between 0.5ppm and 1.0ppm, and the fluctuation range of hydrogen concentration per unit hour is ≤±0.05~0.1ppm. No food should be added during this period, only water changes or additives can be added. The water temperature should be maintained at 20~23℃, dissolved oxygen above 8.0mg / L, pH at 7.0~8.5, and the ammonia nitrogen content should be <0.2mg / L and the nitrite content should be <0.02mg / L.

[0007] According to a preferred embodiment of the present invention, before transporting the fish in S1, the fish transport box is disinfected with salt water in advance, and during the transport of grass carp, the hydrogen concentration in the water of the fish transport box is 0.3 mg / L, and the fluctuation concentration shall not exceed 0.01 mg / L.

[0008] According to a preferred embodiment of the present invention, the aeration time in S2 is 12-24 hours, and the salinity of the water is controlled between 4‰ and 5‰.

[0009] According to a preferred embodiment of the present invention, during the period of hydrogen-rich water circulation and fasting, the water is changed every 10 days, and the water level is not less than 1 / 2 of the whole tank. After the water is changed, the salinity is adjusted to maintain a salinity of 4‰-5‰.

[0010] According to a preferred embodiment of the present invention, during the period of hydrogen-rich water circulation and fasting, the operating flow rate v2 of the circulating water pump and the total water volume v1 of the aquaculture pond satisfy the proportional relationship v2=k×v1, wherein the circulation ratio k is 7.19~7.81 times / h.

[0011] According to a preferred embodiment of the present invention, the period of fasting and temporary rearing in hydrogen-rich water circulation is 55-65 days.

[0012] According to a preferred embodiment of the present invention, the additives include aquatic gallnut powder, Australian Vita, mixed killing agent, ring disinfectant, compound iodine, and non-iodized sun-dried salt.

[0013] This invention also provides a hydrogen-rich water recirculating fasting temporary rearing system for the aforementioned grass carp recirculating aquaculture system for quality restoration and conditioning. The system includes at least a rearing tank, an aerator, a hydrogen generator, an external circulation system, a temperature control system, and a water quality monitoring device. The external circulation system includes an external circulation pipeline, a circulating water pump installed in the pipeline, a protein skimmer, a physical filtration device, and a biological treatment tank. The aerator and hydrogen generator are located at the bottom of the rearing tank. The temperature control system and water quality monitoring device are located inside the rearing tank and are used to measure water temperature, salinity, dissolved oxygen, pH, ammonia nitrogen content, and... Nitrite content; the inlet of the external circulation pipeline is connected to the bottom of the side wall of the breeding tank, and a protein separator, a physical filter and a biological treatment tank are sequentially installed on the external circulation pipeline; a circulating water pump is installed on the external circulation pipeline to provide circulation power, the protein separator is used to filter protein and impurities in the water; the physical filter is an ultraviolet sterilization device for water sterilization, and the biological treatment tank is used to biologically treat ammonia nitrogen and nitrite in the water; the outlet of the external circulation pipeline is connected to the inlet of the breeding tank to realize the external circulation of water; a tailwater treatment port is set at the bottom of the breeding tank.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. Synergistic regulation of fasting and hydrogen-rich water circulation: By combining hydrogen-rich water circulation regulation with fasting and temporary holding, the problems of decreased fish immunity and disease outbreaks under the traditional fasting mode are avoided. While optimizing the quality of fish meat, the basic body shape of the fish is maintained, ensuring a high survival rate of grass carp during the temporary holding process and improving aquaculture efficiency.

[0015] 2. Precise Water Quality Control: This patented invention utilizes a water quality control system to achieve real-time monitoring and adjustment of key water quality parameters such as dissolved oxygen, pH, and salinity within the rearing tank. This water quality control ensures that the water quality remains within the optimal range for grass carp growth, effectively preventing adverse effects on the fish due to water quality fluctuations.

[0016] 3. Scalability and Systemic Approach: This patent is scalable and can be customized to meet the needs of different farmed fish species and growth stages. The system is complete and easy to promote. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the hydrogen-rich water circulating fasting and temporary holding system in an embodiment of the present invention.

[0018] In the diagram, 1. Aquaculture tank, 2. Protein separator, 3. Physical filtration device, 4. Biochemical treatment tank, 5. Temperature control and water quality monitoring device, 6. Hydrogen generator, 7. Aerator, 8. Inlet, 9. Wastewater treatment outlet. Detailed Implementation

[0019] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0020] To implement the grass carp recirculating aquaculture system for food restriction and conditioning, this invention constructs a hydrogen-rich water recirculating aquaculture system for temporary holding without food. Figure 1 As can be seen, the system includes a breeding tank 1, an aerator 7, a hydrogen generator 6, an external circulation system, a temperature control and water quality monitoring device 5; wherein, the external circulation system includes an external circulation pipeline, a circulating water pump installed in the pipeline, a protein separator 2, a physical filtration device 3, and a biochemical treatment tank 4.

[0021] The aquaculture pond is made of food-grade PP material, which can form initial and secondary water swirls to push feces, uneaten feed, and other waste into the drain, thus achieving the pond's self-cleaning ability. The aerator 7 requires an aeration area of ​​≥90cm². 2 Pressure ≥ 2 bar. Water quality testing and temperature control device: This device ensures that the water temperature (temperature 20-23℃) and pH value (slightly alkaline pH of about 8.0) in the breeding pond are kept constant within a suitable range, thereby improving the growth rate and survival rate of the experimental fish.

[0022] An aerator 7 and a hydrogen generator 6 are installed at the bottom of the culture tank 1. A temperature control and water quality monitoring device 5 is located inside the culture tank to measure parameters such as water temperature, salinity, dissolved oxygen, pH, ammonia nitrogen content, and nitrite, thereby improving the growth rate and survival rate of the experimental fish. The inlet of the external circulation pipeline is connected to the bottom of the side wall of the culture tank. A protein separator 2, a physical filter 3, and a biological treatment tank 4 are sequentially installed on the external circulation pipeline. A circulating water pump is installed on the external circulation pipeline to provide circulation power. The protein separator is used to filter protein and impurities in the water. The physical filter is an ultraviolet sterilization device for water sterilization. The biological treatment tank is used to biologically treat ammonia nitrogen and nitrite in the water. The outlet of the external circulation pipeline is connected to the inlet 8 of the culture tank to realize the external circulation of the water. A tailwater treatment port 9 is provided at the bottom of the culture tank.

[0023] Furthermore, according to a preferred embodiment of the present invention, the pipe assembly connections are made of PVC-U material. The biochemical treatment tank is filled with a nitrifying bacteria membrane to decompose and transform dissolved organic matter (such as COD) and nitrogen source pollutants such as ammonia nitrogen. The physical filtration device includes a microfiltration tank, which contains filter bags and a buffer tank, and also includes an ultraviolet sterilizer (preferably ultraviolet light with a wavelength of 253.7 nanometers).

[0024] The core idea of ​​this invention is to employ a synergistic regulation of fasting and hydrogen-rich water circulation to avoid the problems of decreased fish immunity and disease outbreaks associated with traditional fasting methods. This optimizes fish meat quality while maintaining the basic body structure, ensuring a high survival rate for grass carp during temporary rearing and improving aquaculture efficiency. During the hydrogen-rich water circulation fasting period, the hydrogen generator and aerator operate in tandem, with the circulating water pump running continuously. The hydrogen concentration in the rearing tank is controlled between 0.5 ppm and 1.0 ppm, with hourly fluctuations ≤ ±0.05~0.1 ppm. No food is added during this period; only water changes or additives are permitted. The water temperature is maintained at 20~23℃, dissolved oxygen above 8.0 mg / L, pH at 7.0~8.5, and ammonia nitrogen <0.2 mg / L and nitrite <0.02 mg / L. Through water quality control, the water quality is consistently maintained within the optimal range for grass carp growth, effectively preventing adverse effects caused by water quality fluctuations.

[0025] All additives used in the embodiments of this invention are commercially available. The Aolong Vita includes vitamin A, vitamin E, B vitamins, and the nutrient enhancer glucose (carrier); the aquatic gallnut powder contains gallic acid; the ring-dissolving agent contains a protein lysing agent, surfactant, and penetrant; and the mixed-killing agent contains abamectin, used to eliminate Trichodina, Dactylogyrus, Chilodonella, ciliates, and anchor crocodiles in the water. The ring-dissolving agent was purchased from the Guangdong Fish and Shrimp Disease Prevention and Control Center, the mixed-killing agent from Shanxi Weiliwo Biotechnology Co., Ltd., the Aolong Vita from Dongfang Aolong Aquatic Products, and the aquatic gallnut powder from Hubei Nongbin Biotechnology Co., Ltd.

[0026] Example 1: (1) Purchase healthy grass carp, choosing those that are disease-free, uninjured, and uniform in size, with each fish weighing approximately 1.25 kg. The transport tanks should be disinfected with 2% saline solution in advance, and the grass carp should be transported with hydrogen at a concentration of 0.3 mg / L for 6 hours.

[0027] (2) After purchasing grass carp, they should be temporarily kept in a breeding pond for 6 months without any artificial feeding. During this period, they are allowed to consume microorganisms and plankton. During the temporary keeping period, the health status of grass carp should be continuously observed, and samples should be taken for testing every day.

[0028] (3) Two to three days before transferring grass carp to the rearing tanks, the rearing tanks should be circulated with water (the water volume in the rearing tanks should be maintained at 3.2 m³).3 Turn on the aerator and aerate for 12-24 hours. After the water intake is complete, add salt to bring the salinity to between 4‰ and 5‰. The salinity should be maintained between 4‰ and 5‰ before and after water changes.

[0029] (4) Grass carp are placed in a rearing tank and temporarily kept in hydrogen-rich water with a fasting period of 60 days. The hydrogen concentration in the rearing water must be ≥0.5ppm. No food should be added during this period; only water changes or additives can be added. The parameters remain basically unchanged during the rearing process, maintaining a temperature of 20-23℃, dissolved oxygen above 8.0mg / L, and a slightly alkaline pH of around 8.0. The hydrogen generator and aeration disc operate in conjunction, serving as the core equipment of the rearing system. During operation, the hydrogen concentration fluctuates within the range of ≤±0.05~0.1ppm. Water quality is tested daily based on the water quality monitoring and temperature control devices.

[0030] (5) During the aquaculture process, the circulating water pump runs continuously. The circulating pump has two flow modes: 23,000 L / H for mode one and 25,000 L / H for mode two. The circulating pump usually operates in mode one. If a sudden situation such as fish disease occurs in the aquaculture pond, switch to mode two. The outlet is tilted at about 45° to push the water in the tank to rotate and flow, and the grass carp swim with the current. The chemical content of the aquaculture pond is tested daily. The ammonia nitrogen content should be <0.2 mg / L and the nitrite content should be <0.02 mg / L to confirm that the biological treatment tank is working normally.

[0031] (6) Water quality and nutrition control: During the breeding process, the following additives need to be added according to the time. Days 0-1: Add 12.8kg-16.0kg of non-iodized sun-dried salt to maintain salinity at 4‰-5‰; Day 2: Add 9.6ml of aquatic gallnut powder; Day 3: Add 16.0g of Australian Dragon Vitamins; Day 4: Add 9.6ml of aquatic gallnut powder; Days 5-8: Add 16.0g of Australian Dragon Vitamins; Days 9-11: Add 9.6ml of aquatic gallnut powder; Days 12-16: Add 9.6ml of aquatic gallnut powder; Days 17-18: Add 2.24ml of Mixed Killer; Days 19-21: Add 2.24ml of Mixed Killer; Days 21-23: Add 4.8g of Ring-Clearing Agent; Days 23-26: Add 3.2ml of Mixed Killer; Days 26-29: Add 16.0kg of non-iodized sun-dried salt and 4.8g of... For the following treatments: Add 6.4ml of compound iodine and 2.24ml of mixed disinfectant at 29-32 days; add 16.0kg of non-iodized sun-dried salt and 3.2ml of mixed disinfectant at 32-41 days; add 9.6ml of mixed disinfectant at 41-45 days; add 22.4g of ring disinfectant at 45-50 days; and add 25.6g of Australian vitamins at 50-60 days. The above dosages ensure consistent concentrations of water quality and meet the health needs of the farmed organisms at each stage.

[0032] (7) Fish samples were taken on days 0, 5, 10, 20, 35, and 60. The body weight, length, and back thickness were measured at the thickest point between the lateral lines on both sides. The circumference, intestinal length, and fatness were also measured. The back muscle of the fish was cut into pieces with a length, width, and thickness of 3cm × 2cm × 1cm for texture analysis of hardness, adhesiveness, elasticity, cohesiveness, gelatinization, and chewiness. Back muscle from different parts of the fish was taken, washed, dried with absorbent paper, chopped, and mixed. The content of moisture, crude protein, crude fat, crude ash, and volatile flavor compounds (compounds with a fishy smell, such as hexanal, octanal, heptanal, and pentadecane) were evaluated. Sensory evaluation analysis was also performed on the steamed fish samples, including color, muscle texture, aroma of cooked fish, off-flavor, tenderness, elasticity, juiciness, umami, sweetness, and fishy smell. After sampling the fish meat, the fatty acids (EHA, DHA) were determined.

[0033] The overall texture analysis was performed using a Plus C texture analyzer. The organ index is the ratio of organ weight to body weight. Moisture content was determined using an MS-70 rapid moisture analyzer. Crude protein was determined using a K9860 fully automated Kjeldahl nitrogen analyzer. Crude fat was determined using a SOX406 fat analyzer. Crude ash was determined using a KSL-1200X muffle furnace. Hexanal, octanal, heptanal, and pentadecane were determined using a Trace1300-ISQ gas chromatography-mass spectrometry system.

[0034] The above data results are shown in Tables 1 to 6 below.

[0035] Table 1 shows that during the 0-60 day period of hydrogen-rich water circulation and fasting, there were no significant differences in the weight, body length, and intestinal length of grass carp, although the fatness decreased slightly, and the basic body shape framework of the fish was maintained overall. The fasting and temporary rearing step in the method of this invention can achieve moderate fat reduction while maintaining the basic body shape framework of grass carp, avoiding the problems of emaciation and deformity caused by traditional fasting, and ensuring the appearance quality of marketable fish.

[0036] The data in Table 2 show that the dry weight fluctuated little over 60 days; the crude ash content fluctuated and decreased over 60 days; and the crude protein and crude fat remained at high levels over 60 days. This achieved dynamic optimization of muscle nutrition components, significantly increased crude protein content, reduced redundant crude ash, regulated fat to a reasonable range, and enhanced the nutritional value of muscle.

[0037] Table 3 shows that hardness, adhesiveness, and chewiness all reach their optimal levels at 10 days, significantly higher than at 0 days; elasticity continues to improve over 60 days; there are no significant differences in adhesion and cohesion, with the best muscle firmness and chewiness in the mid-term, and continuous improvement in elasticity in the long term. This optimizes the texture of grass carp meat, meeting consumers' demands for tenderness and elasticity.

[0038] The data in Table 4 show that after fasting and temporary rearing, the color, texture, tenderness, odor, and overall preference score of grass carp were significantly improved, which comprehensively optimized the sensory quality of grass carp, reduced odor and fishy smell, and increased the market acceptance of commercial fish.

[0039] The data in Table 5 show that during the fasting period, the levels of threonine and isoleucine in the essential amino acids increased significantly; the levels of serine and alanine in the umami amino acids increased significantly; and the core amino acids remained stable or fluctuated positively overall.

[0040] It ensures and enhances the content of essential amino acids and umami amino acids in the muscle, providing core support for the nutritional value and flavor of grass carp muscle and strengthening the product's nutritional competitiveness.

[0041] Table 6 shows that during the fasting period, the content of eicosapentaenoic acid (EPA) in polyunsaturated fatty acids increased by approximately 57.0%, and the content of docosahexaenoic acid (DHA) increased by 48.6%. Saturated fatty acids and monounsaturated fatty acids, after dropping to lower levels for 35 days, showed a reasonable rebound, with the overall proportion of polyunsaturated fatty acids remaining stable and showing a phased increase. Stabilizing and increasing the content of key polyunsaturated fatty acids such as EPA and DHA enhances the nutritional value of unsaturated fatty acids in grass carp muscle, meeting the needs of a healthy diet. EPA and DHA are essential nutrients for the human body, helping to promote the development of the nervous system and improve immunity. Therefore, the nutritional quality of grass carp was significantly enhanced after hydrogen-rich water circulation fasting.

[0042] Table 1. Morphological parameters and standard deviations of grass carp (n=5) Table 2. Comparative analysis of moisture, crude ash, crude protein and crude fat in grass carp (n=5) Table 3. Texture properties (n=5) Table 4. Sensory evaluation of grass carp muscle before and after fasting (n=5) Table 5. Effects of fasting on amino acid content in grass carp muscle (n=5) Table 6. Effects of fasting on fatty acids in grass carp In summary, this study shows that grass carp, after fasting and temporary rearing, exhibited almost no change in body shape, but local indicators were adjusted, and the muscle nutritional composition was dynamically optimized, with improved crude protein levels. Sensory evaluation revealed a continuous improvement in taste, with significant improvements in the firmness and chewiness of the grass carp meat, resulting in overall optimized sensory quality. The levels of core essential amino acids and umami-related amino acids remained stable or increased, ensuring the nutritional value and flavor foundation of the muscle. The overall EPA and DHA proportions remained stable and showed a phased increase, guaranteeing the nutritional value of unsaturated fatty acids in the muscle.

[0043] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0044] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system, characterized in that, Includes the following steps: S1. Commercial grass carp are transported to breeding ponds and temporarily kept for 5-7 months without any artificial feeding. S2. Construct a hydrogen-rich water circulation fasting temporary rearing system, the system including at least a rearing tank, an aerator, a hydrogen generator, an external circulation system, a temperature control system, and a water quality monitoring device; wherein, the external circulation system includes an external circulation pipeline, a circulating water pump installed in the pipeline, a protein separator, a physical filtration device, and a biological treatment tank; before the grass carp are transferred into the rearing tank, water is circulated in the rearing tank and the aerator is turned on for aeration, and salt is added after the water intake is completed to control the salinity of the water; S3. After temporary rearing in S1, the grass carp are transferred to the rearing tanks treated in S2 for temporary rearing in hydrogen-rich water circulation without feeding. During the temporary rearing period, the hydrogen generator and aerator operate in conjunction, and the circulating water pump runs continuously throughout the process. The hydrogen concentration in the water in the rearing tank is controlled between 0.5ppm and 1.0ppm, and the fluctuation range of hydrogen concentration per unit hour is ≤±0.05~0.1ppm. No food should be added during this period, only water changes or additives can be added. The water temperature should be maintained at 20~23℃, dissolved oxygen above 8.0mg / L, pH at 7.0~8.5, and the ammonia nitrogen content should be <0.2mg / L and the nitrite content should be <0.02mg / L.

2. The method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system as described in claim 1, characterized in that, Before transporting the fish, the transport boxes must be disinfected with salt water. During the transport of grass carp, the hydrogen concentration in the water of the transport boxes must be 0.3 mg / L, and the fluctuation concentration must not exceed 0.01 mg / L.

3. The method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system as described in claim 1, characterized in that, In S2, the aeration time is 12-24 hours, and the salinity of the water is controlled between 4‰ and 5‰.

4. The method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system as described in claim 1, characterized in that, During the period of hydrogen-rich water circulation and fasting, the water should be changed every 10 days, and the water level should not be lower than 1 / 2 of the whole tank. After changing the water, the salinity should be adjusted to maintain a salinity of 4‰-5‰.

5. The method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system as described in claim 1, characterized in that, During the hydrogen-rich water circulation and fasting period, the working flow rate v2 of the circulating water pump and the total water volume v1 of the aquaculture pond satisfy the proportional relationship v2=k×v1, where the circulation ratio k is 7.19~7.81 times / h.

6. The method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system as described in claim 1, characterized in that, The period of fasting and temporary rearing with hydrogen-rich water circulation is 55-65 days.

7. The method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system as described in claim 6, characterized in that, The additives include aquatic gallnut powder, Australian Vita, Mixed Killer, Ring Disinfectant, compound iodine, and non-iodized sun-dried salt.

8. The method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system as described in claim 7, characterized in that, The aquaculture water volume is 3.2 m³. 3 The hydrogen-rich water circulation fasting period is 60 days. The additive addition process is as follows: Days 0-1: Add 12.8kg-16.0kg of non-iodized sun-dried salt to maintain a salinity of 4‰-5‰; Day 2: Add 9.6ml of aquatic gallnut powder; Day 3: Add 16.0g of Australian Dragon Vitamins; Day 4: Add 9.6ml of aquatic gallnut powder; Days 5-8: Add 16.0g of Australian Dragon Vitamins; Days 9-11: Add 9.6ml of aquatic gallnut powder; Days 12-16: Add 9.6ml of aquatic gallnut powder; Days 17-18: Add 2.24ml of Mixed Killer; Days 19-21: Add 2.24ml of Mixed Killer; Days 21-23: Add 4.8g of Ring-Clearing Agent; Days 23-26: Add 3.2ml of Mixed Killer; Days 26-29: Add 16.0kg of non-iodized sun-dried salt and 4.8g of... Ring disinfectant; add 6.4ml of compound iodine and 2.24ml of mixed disinfectant on days 29-32; add 16.0kg of non-iodized sun-dried salt and 3.2ml of mixed disinfectant on days 32-41; add 9.6ml of mixed disinfectant on days 41-45; add 22.4g of ring disinfectant on days 45-50; add 25.6g of Australian Vitamin on days 50-60.

9. The method for restoring and conditioning the quality of grass carp in a recirculating aquaculture system as described in claim 1, characterized in that, The aerator and hydrogen generator are located at the bottom of the aquaculture tank; the temperature control and water quality monitoring device is located inside the aquaculture tank to measure water temperature, salinity, dissolved oxygen, pH, ammonia nitrogen content, and nitrite content; the inlet of the external circulation pipeline is connected to the bottom of the side wall of the aquaculture tank, and a protein separator, a physical filter, and a biological treatment tank are sequentially installed on the external circulation pipeline; a circulating water pump is installed on the external circulation pipeline to provide circulation power, the protein separator is used to filter protein and impurities in the water; the physical filter is an ultraviolet sterilization device for water sterilization, and the biological treatment tank is used to biologically treat ammonia nitrogen and nitrite in the water; the outlet of the external circulation pipeline is connected to the inlet of the aquaculture tank to realize the external circulation of water; a tailwater treatment port is provided at the bottom of the aquaculture tank.

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