A fishing device and method for reducing stress damage in salmon and trout

Abstract

This invention belongs to the field of aquaculture technology and relates to a harvesting device and method for reducing stress damage in salmon and trout. The system systematically constructs a structure including a rearing pond, a harvesting pond, a transfer channel, and a V-shaped collection port, independently separating salmon and trout rearing from harvesting operations for easier management. Based on this device, a non-destructive harvesting method is developed. This method comprehensively utilizes pre-harvest environmental adaptation, ice-salt combined low-temperature anesthesia during harvesting, and post-harvest gradient recovery to construct a complete stress protection system. Pre-harvest temperature and light gradient acclimatization and fasting treatment reduce the fish's baseline stress level; the physical heat absorption of the ice-salt mixture achieves rapid, chemical-free anesthesia and sedation; and gradual gradient recovery helps the fish recover smoothly and prevents secondary stress. These three stages support each other and progress step by step, systematically reducing harvesting stress damage from the source, process, and end.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture technology and relates to a fishing device and method for reducing stress damage in salmon and trout. Background Technology

[0002] Salmon and trout (including Atlantic salmon and rainbow trout) are important cold-water economic fish species with extremely high edible and market value. With the continuous development of aquaculture technology, the scale of salmon and trout farming is constantly expanding, and the requirements for its harvesting efficiency and fish quality are also increasing.

[0003] However, the following prominent technical challenges exist in salmon and trout fishing: (1) Severe stress damage: In traditional net fishing operations, fish struggle violently and collide with each other in the net, which can easily cause scale loss, skin damage, or even death. Studies have shown that mechanical damage and physiological stress during fishing can lead to a certain percentage of immediate or delayed deaths. (2) Lack of pre-fishing stress management: Existing fishing methods hardly consider pre-fishing stress management. Fish go directly from normal aquaculture to fishing operations, resulting in severe stress reactions. (3) Risk of chemical anesthetic residues: Existing studies have shown that anesthesia is one of the main ways to alleviate fish stress, but existing anesthesia methods are mostly targeted at the transportation stage and require the addition of chemical anesthetics (such as eugenol, MS-222, etc.) to the water, which poses drug residue and food safety risks.

[0004] To address the aforementioned issues, some improvements have been proposed in existing technologies. For example, Ocean University of China disclosed a device and method for harvesting cold-water fish from large aquaculture cages in summer (CN202110327491.0). This method guides the fish school through a fish collection section and a fish guide channel, but it does not address pre-harvest environmental adaptation management or anesthetize the fish. The South China Sea Fisheries Research Institute disclosed a non-destructive continuous suction method and system (CN202311119384.4), which achieves non-destructive suction through a fish induction system and suction power control, but similarly, it does not address pre-harvest stress management or low-temperature anesthesia. The Shandong Marine Biology Research Institute disclosed a low-temperature anesthesia transportation method for live spotted trout (CN105210943B), but this method only addresses the transportation stage and requires the addition of chemical anesthetics.

[0005] Therefore, there is an urgent need to develop a non-destructive fishing device and method for salmon and trout that can systematically reduce stress damage throughout the fishing process, achieve selective fishing, and eliminate the need for chemical anesthetics. Summary of the Invention

[0006] To address the shortcomings of the prior art, this invention provides a fishing device and method for reducing stress damage in salmon and trout, which can overcome the defects of the prior art, such as severe stress damage during salmon and trout fishing, lack of pre-fishing stress management, and possible chemical anesthetic residues.

[0007] The present invention discloses a fishing device for reducing stress damage in salmon and trout, comprising a culture pond and a harvesting pond, wherein a transfer channel is connected between the culture pond and the harvesting pond, a pipe plug is provided at one end of the transfer channel located in the culture pond, a plurality of filter holes are provided at the bottom of the transfer channel, and a V-shaped collection port is provided below the filter holes, and the V-shaped collection port returns the water to the culture pond through a pipeline.

[0008] As a preferred embodiment, the inner diameter of the transfer channel is 1.5-2 times the average height of the fish.

[0009] The present invention also provides a fishing method for reducing stress damage in salmon and trout, using the above-described fishing device and following these steps:

[0010] (1) Environmental pre-adaptation before fishing: 7-14 days before fishing, gradually reduce the water temperature and light conditions of the breeding pond to acclimate salmon and trout to anti-stress before fishing.

[0011] (2) Guiding and transporting: After the environmental pre-adaptation is completed, place a fishing net on the side of the breeding pond away from the transfer channel, remove the pipe plug on the transfer channel, and then manually pull the fishing net to move it to the side of the transfer channel to drive the salmon and trout into the harvesting pond through the transfer channel.

[0012] (3) Low temperature anesthesia and sedation: Seawater cooled to 1~3℃ is injected into the harvesting pool beforehand. After all the salmon and trout in the breeding pool are transferred to the harvesting pool, the transfer channel is sealed with a pipe plug. Then, ice salt mixture is added to the harvesting pool to lower the water temperature to 0.5~2℃ within 1~2 minutes. Then, the salmon and trout stay in this environment for 3~5 minutes to allow the fish to enter a deep sedation state.

[0013] (4) Non-destructive capture and transfer: Transfer salmon and trout in a deep sedated state from the capture pool to the transport vehicle.

[0014] As a preferred option, the above-mentioned fishing method also includes step (5) gradient recovery: the fish in the transport vehicle are transferred to gradient recovery tanks with water temperatures of 8℃, 12℃ and 16℃ in sequence, and each gradient is maintained for 5 to 10 minutes. After the fish completes the gradient recovery, it regains its ability to swim independently.

[0015] As a preferred option, in step (1), the water temperature of the aquaculture pond is reduced to 12-15℃ at a rate not exceeding 1℃ / day, so that the fish can gradually adapt to the target water temperature environment before harvesting; the light conditions of the aquaculture pond are reduced to 100-200 lux at a rate not exceeding 50 lux / day, to simulate the light environment during harvesting operations, so that the fish can gradually adapt to the light stimulation of harvesting operations.

[0016] As a preferred option, in step (1), feeding is stopped 48-72 hours before harvesting to reduce the metabolic burden and stress response of fish during the harvesting process, while reducing the impact of digestive contents on meat quality. During the period of fasting, the dissolved oxygen content in the aquaculture pond is kept not less than 6 mg / L.

[0017] As a preferred option, in step (2), the side of the breeding pond near the transfer channel is treated to avoid light, with a light intensity ≤10 lux, to help the fish population accumulate by utilizing the enhanced activity characteristics of salmonids in low light environments.

[0018] As a preferred embodiment, in step (3), the ice-salt mixture is made by mixing food-grade crushed ice and food-grade salt in a mass ratio of 3-5:1.

[0019] As a preferred embodiment, the food-grade salt is food-grade sodium chloride, food-grade potassium chloride, or food-grade magnesium chloride.

[0020] As a preferred option, in step (4), salmon and trout in a deep sedation state are transferred from the fishing pond to a transport vehicle using a variable frequency centrifugal fish suction pump or conveyor belt.

[0021] The advantages of this invention are:

[0022] (1) The present invention provides a fishing device suitable for reducing stress damage to salmon and trout. It systematically constructs a structure including a culture pond, a harvesting pond, a transfer channel and a V-shaped collection port, which separates the culture and harvesting operations of salmon and trout, making it convenient for operation and management.

[0023] (2) This invention provides a non-destructive fishing method to reduce fishing stress damage in salmon and trout. This method comprehensively utilizes pre-fishing environmental pre-adaptation, ice-salt combined low-temperature anesthesia during fishing, and post-fishing gradient recovery to construct a full-process stress protection system. The basic stress level of the fish is reduced by temperature and light gradient acclimatization and fasting treatment before fishing. Rapid and chemical-free anesthesia and sedation are achieved through physical heat absorption of the ice-salt mixture. Gradual recovery helps the fish recover smoothly and prevents secondary stress. The three links support each other and progress step by step, systematically reducing fishing stress damage from the source, process and end.

[0024] (3) This invention can not only effectively reduce the mortality rate during the fishing process and improve the integrity rate of fish scales and skin, but also improve the survival rate of live fish during transportation and enhance the quality of fish meat. No chemical anesthetics are added throughout the process, and there is no risk of drug residues. This invention can promote the upgrading of salmon and trout fishing operations towards low stress, low damage, and high efficiency, and has important industrial application value and promotion prospects. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of Example 1;

[0027] In the diagram: 1. Aquaculture pond; 2. Harvesting pond; 3. Transfer channel; 4. Filter hole; 5. V-shaped collection port. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] In the description of this invention, it should be noted that the terms indicating orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0030] Example 1:

[0031] A fishing device for reducing stress damage in salmon and trout includes a rearing pond 1 and a harvesting pond 2. A transfer channel 3 connects the rearing pond 1 and the harvesting pond 2. A pipe plug is provided at one end of the transfer channel 3 located in the rearing pond 1. Several filter holes 4 are provided at the bottom of the transfer channel 3. A V-shaped collection port 65 is provided below the filter holes 4. The V-shaped collection port 65 returns the fish to the rearing pond through a pipeline.

[0032] In one specific implementation, the inner diameter of the transfer channel 3 is 1.5-2 times the average height of the fish.

[0033] In this context, the rearing pond 1 refers to a water container used for the daily rearing of salmon and trout, typically equipped with a circulating water pipeline. Its shape, size, and material can be determined according to the actual scale of rearing; for example, it can be a rectangular pond constructed of concrete, or a circular or polygonal pond made of fiberglass or high-density polyethylene. This embodiment does not impose any special limitations on this. In this technical solution, the rearing pond 1 serves as the initial rearing environment for the fish, and its internal water quality, temperature, and lighting conditions can be adjusted according to rearing needs. The rearing pond 1 is connected to the transfer channel 3, forming the starting point for the outward migration of the fish. Its function is to provide a stable source environment, ensuring that the fish are in a relatively calm state before entering the transfer process.

[0034] The structure of the harvesting pond 2 can be set according to the actual situation. For example, it can be a fixed pond independent of the breeding pond, or it can be a movable temporary water storage tank. The harvesting pond 2 is connected to the breeding pond 1 through the transfer channel 3. After the fish are transferred, the environmental parameters (such as temperature) in the harvesting pond 2 can be independently controlled to make the fish enter a specific physiological state, thereby achieving harvesting without damage.

[0035] The inner diameter of the transfer channel 3 is approximately 350-400 mm, and its inner wall can be coated with silicone material. The cross-section can be circular, square, or elliptical; this embodiment does not impose any particular limitation on this. The transfer channel 3 is preferably arranged at an angle, with one end in the aquaculture pond 1 higher than the end in the harvesting pond 2. The filter holes 4 at the bottom of the transfer channel 3 are used to separate the water from the fish. The water flows back to the aquaculture pond 1 through a V-shaped collection port 5, pipes, and a water pump, ensuring that the water level in the aquaculture pond 1 is always higher than the inlet of the transfer channel 3. To further maintain the water level, the inlet of the circulating water pipe in the aquaculture pond can be opened to replenish the water as needed.

[0036] Example 2:

[0037] A non-destructive fishing method to reduce stress damage during Atlantic salmon fishing, comprising the following steps:

[0038] The farmed species is Atlantic salmon (Salmo salar), with an average weight of 5.0 kg and an average body length of 65 cm. The farming environment is a land-based recirculating aquaculture system with a water temperature of 14℃ and a water depth of 2.5 m.

[0039] (1) Environmental pre-acclimatization before harvesting: This step aims to reduce the basal stress level of the fish population from the source and reduce the cortisol peak caused by subsequent harvesting operations. The water temperature is gradually adjusted by the refrigeration unit or heat exchange system, and the light conditions are adjusted by the dimmable LED lighting system or shading curtains. Specifically, starting 10 days before harvesting, the culture water temperature is gradually reduced from 14℃ to 13℃ at a rate of 0.5℃ / day, so that the fish population can gradually adapt to the target water temperature environment before harvesting; the light intensity is gradually reduced from 1000 lux to 150 lux at a rate of 50 lux / day to simulate the light environment during harvesting operations, so that the fish population can gradually adapt to the light stimulation of harvesting operations; feeding is stopped 48 hours before harvesting to reduce the metabolic burden and stress response of the fish during the harvesting process, while reducing the impact of digestive contents on meat quality and maintaining dissolved oxygen at no less than 6 mg / L. Atlantic salmon are subjected to anti-stress acclimatization before harvesting.

[0040] (2) Guided transport: After environmental pre-acclimatization, a fishing net is placed on the side of the aquaculture pond away from the transfer channel. The plug on the transfer channel is removed, and then the fishing net is manually pulled slowly towards the transfer channel. Utilizing the fish's instinctive behavior of avoiding the net, they are smoothly driven to the entrance of the transfer channel. At the same time, the side of the aquaculture pond closest to the transfer channel is protected from light, with a light intensity ≤10 lux. The increased activity of salmon and trout in low-light environments helps to enrich the fish population. This non-violent guiding method effectively avoids the mechanical damage caused by the violent struggle of the fish in traditional purse seine fishing, achieving a lossless transfer of the fish from the aquaculture pond to the harvesting pond.

[0041] (3) Low-temperature anesthesia and sedation: Seawater cooled to 2°C (salinity 30‰) is pre-filled into the harvesting tank. After all the Atlantic salmon in the rearing tank are transferred to the harvesting tank, the transfer channel is sealed with a plug. Then, an ice-salt mixture (a mixture of food-grade crushed ice and food-grade sodium chloride at a mass ratio of 4:1) is added to the harvesting tank, causing the water temperature to drop to 0.5-2°C within 1-2 minutes. The Atlantic salmon then remain in this environment for 4 minutes, allowing the fish to enter a state of deep sedation. Low-temperature anesthesia and sedation utilizes physical cooling methods to block nerve conduction in the fish, thus inducing a dormant state. This step completely replaces chemical anesthetics, eliminating the risk of drug residues. The ice-salt mixture utilizes the principle of ice-salt eutectic; the dissolution of salts absorbs heat, rapidly lowering the water temperature. When the fish remains in this low-temperature environment, its core body temperature decreases, its metabolic rate slows significantly, and it enters a state of deep sedation. This combination of rapid physical cooling and short-term residence ensures both the anesthesia effect and avoids frostbite or hypoxia damage caused by prolonged low temperatures.

[0042] (4) Non-destructive capture and transfer: Start the variable frequency centrifugal fish suction pump, adjust the pump speed to 800 rpm, and set the inner diameter of the fish suction pipe to 350 mm with a smooth polytetrafluoroethylene lining on the inner wall. Transfer the deeply sedated Atlantic salmon to the transport vehicle through the fish suction pipe. Non-destructive capture and transfer is the process of safely loading the sedated fish into the transport vehicle. This step is based on the premise that the fish is in a state of deep sedation and temporarily loses its ability to move. Because the fish is sedated, it will not struggle or collide with the pipe, thus ensuring the integrity of the scales and the absence of damage to the skin.

[0043] (5) Processing: For Atlantic salmon that need to be processed directly, bloodletting and viscera removal are performed while the salmon is in a sedated state.

[0044] Experimental Results: Using the method of this invention, 500 Atlantic salmon were caught. No fish deaths occurred during the catching process, the scale integrity rate was 98.8%, and the epidermal damage rate was only 0.8%. Monitoring results of fish stress indicators showed that the plasma cortisol concentration after catching was 18.5 ng / mL, and the plasma lactate concentration was 2.1 mmol / L. After processing, the fish meat had a bright color and firm texture.

[0045] Example 3:

[0046] A non-destructive fishing method to reduce stress damage from rainbow trout fishing, comprising the following steps:

[0047] The farmed species is rainbow trout (Oncorhynchus mykiss), with an average weight of 2.0 kg and an average body length of 45 cm. The farming environment is a land-based recirculating aquaculture system with a water temperature of 16℃ and a water depth of 2.5 m. The purpose of harvesting is to transport the live animals to a destination 500 kilometers away.

[0048] (1) Environmental pre-acclimatization before harvesting: Starting 7 days before harvesting, the culture water temperature was gradually reduced from 16℃ to 14℃ at a rate of 1℃ / day, allowing the fish to gradually adapt to the target water temperature environment before harvesting; the light intensity was gradually reduced from 400 lux to 200 lux at a rate of 40 lux / day, simulating the light environment during harvesting operations, allowing the fish to gradually adapt to the light stimulation of harvesting operations; feeding was stopped 48 hours before harvesting to reduce the metabolic burden and stress response of the fish during the harvesting process, while also reducing the impact of digestive contents on meat quality, and maintaining dissolved oxygen levels not lower than 6 mg / L. Rainbow trout were subjected to pre-harvest stress acclimatization.

[0049] (2) Guiding and transporting: After the environmental pre-adaptation is completed, place a fishing net on the side of the breeding pond away from the transfer channel, remove the pipe plug on the transfer channel, and then manually pull the fishing net to move slowly to the side of the transfer channel. Utilize the fish’s instinctive behavior of avoiding the net to drive them smoothly to the entrance of the transfer channel. At the same time, take measures to avoid light on the side of the breeding pond close to the transfer channel, with a light intensity ≤10 lux. Utilize the behavior characteristics of salmon and trout that increase activity in low light environment to help the fish population accumulate.

[0050] (3) Low-temperature anesthesia and sedation: Seawater cooled to 2°C (salinity 30‰) is pre-filled into the harvesting tank. After all rainbow trout in the rearing tank are transferred to the harvesting tank, the transfer channel is sealed with a plug. Then, an ice-salt mixture (a mixture of food-grade crushed ice and food-grade sodium chloride at a mass ratio of 3.5:1) is added to the harvesting tank, causing the water temperature to drop to 0.5-2°C within 1-2 minutes. The rainbow trout then remain in this environment for 3.5 minutes, allowing them to enter a state of deep sedation. Low-temperature anesthesia and sedation utilizes physical cooling methods to block nerve conduction in the fish, thus inducing a dormant state. This step completely replaces chemical anesthetics, eliminating the risk of drug residues. The ice-salt mixture utilizes the principle of ice-salt eutectic; the dissolution of salts absorbs heat, rapidly lowering the water temperature. When the fish remain in this low-temperature environment, their core body temperature decreases, their metabolic rate slows significantly, and they enter a state of deep sedation. By combining rapid physical cooling with short-term exposure, the anesthesia effect is ensured while avoiding frostbite or hypoxia damage to the fish caused by prolonged low temperatures.

[0051] (4) Non-destructive capture and transfer: Rainbow trout in a calmed state are transferred to a transport container using a conveyor belt capture device. The conveyor belt speed is 0.3 m / s and the surface is provided with a flexible support layer.

[0052] (5) Gradient Recovery: Rainbow trout were sequentially transferred to gradient recovery tanks with water temperatures of 8℃, 12℃, and 16℃, remaining at each gradient for 8 minutes. After completing the gradient recovery, the fish regained their ability to swim independently. Gradient recovery is a process that helps fish recover normal physiological functions from a low-temperature sedation state by gradually increasing the temperature. This step aims to prevent rewarming shock or secondary stress caused by a sudden increase in temperature. As the water temperature gradually increases, the fish's enzyme activity recovers, the nervous system becomes active again, and finally, the fish regains its ability to swim independently and its sense of balance in the highest temperature gradient tank. Through this gradual rewarming mechanism, the impact of temperature difference is effectively mitigated, ensuring that the fish have a very high survival rate and good growth status after recovery.

[0053] Experimental Results: Using the method of this invention, 800 rainbow trout were caught and transported live to their destination 500 kilometers away. The scale integrity rate was 98.9%, and the epidermal damage rate was only 0.9%. The survival rate during transport reached 99.4%. The fish showed minimal stress response during transport, with plasma cortisol concentration at 20.2 ng / mL and plasma lactate concentration at 2.3 mmol / L. Water quality deterioration was minimal, recovery time upon arrival at the destination was short, and no mortality was observed.

[0054] Comparative Example 1:

[0055] Five hundred Atlantic salmon of the same size as in Example 2 were caught using a traditional purse seine method. During the catch, the fish struggled violently, resulting in dense collisions within the net. After harvesting, 28 dead fish were found (mortality rate 5.6%), with 57% of the fish having intact scales and 43% suffering skin damage. Monitoring of stress indicators showed that the plasma cortisol concentration was 65.3 ng / mL and the plasma lactate concentration was 5.8 mmol / L after harvesting. After processing, the fish meat showed localized congestion and a decline in meat quality.

[0056] Comparative Example 2:

[0057] A comparative experiment was conducted using the apparatus and method disclosed by Ocean University of China for summer harvesting of cold-water fish in large aquaculture cages (CN202110327491.0). 500 Atlantic salmon of the same size as in Example 2 were harvested. The method includes: pumping out high-temperature water from the fish collection section to allow cold bottom water to enter; inducing the fish to enter the collection section using bait and light attractants; guiding the fish through a fish guide channel; and using a fish suction pump for harvesting. The comparative experiment results showed that using this method to harvest 500 Atlantic salmon, 8 fish died during the harvesting process (mortality rate 1.6%), the scale integrity rate was 92.4%, and the epidermal damage rate was 5.6%. Monitoring results of fish stress indicators showed that the plasma cortisol concentration after harvesting was 42.6 ng / mL, and the plasma lactate concentration was 3.8 mmol / L.

[0058] This invention is the first to incorporate pre-harvest environmental adaptation into the harvesting process. Through 7-14 days of temperature and light gradient pre-adaptation and fasting treatment, fish are physiologically and psychologically adapted to the harvesting environment in advance, reducing the baseline level of stress response from the source. Experiments show that fish that have undergone pre-adaptation have a cortisol peak level reduced by approximately 40% during harvesting. This invention uses an ice-salt mixture (ice:salt = 3:1~5:1) as a rapid cooling medium, utilizing the endothermic effect of ice-salt dissolution to achieve rapid cooling. No chemical anesthetics are added throughout the process, completely avoiding the risk of drug residues and meeting food safety requirements. This invention sets up three gradient resuscitation tanks at 8℃-12℃-16℃ to gradually restore the fish to a living state, reducing secondary stress. This invention organically integrates environmental pre-adaptation, induced enrichment, size screening, guided transport, low-temperature anesthesia, non-destructive harvesting, and gradient resuscitation to form a systematic stress management solution covering the entire harvesting process. Each link works synergistically to minimize stress damage to the fish. Through comparison of the above embodiments and comparative examples, the method of the present invention is significantly superior to traditional net-catching methods and existing technologies (CN202110327491.0) in terms of mortality rate, scale integrity rate, epidermal damage rate, and stress physiological indicators. The method of the present invention achieves zero mortality during the fishing process, a scale integrity rate as high as 98.8%, a significant reduction in plasma cortisol concentration compared to existing technologies, and a live transport survival rate of 99.4%, demonstrating significant technological advancement.

[0059] The above is a detailed description of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A fishing apparatus for reducing stress damage in salmon and trout, comprising a culture pond, characterized in that, It also includes a harvesting pond, and a transfer channel is connected between the breeding pond and the harvesting pond. A pipe plug is set at one end of the transfer channel in the breeding pond. Several filter holes are opened at the bottom of the transfer channel. A V-shaped collection port is set below the filter holes. The V-shaped collection port returns the water to the breeding pond through a pipeline.

2. A fishing device for reducing stress damage in salmon and trout according to claim 1, characterized in that, The inner diameter of the transfer channel is 1.5-2 times the average height of the fish.

3. A fishing method for reducing stress damage in salmon and trout, characterized in that, The fishing apparatus according to claim 1 is used in accordance with the following steps: (1) Environmental pre-adaptation before fishing: 7-14 days before fishing, gradually reduce the water temperature and light conditions of the breeding pond to acclimate salmon and trout to anti-stress before fishing. (2) Guiding and transporting: After the environmental pre-adaptation is completed, place a fishing net on the side of the breeding pond away from the transfer channel, remove the pipe plug on the transfer channel, and then manually pull the fishing net to move it to the side of the transfer channel to drive the salmon and trout into the harvesting pond through the transfer channel. (3) Low temperature anesthesia and sedation: Seawater cooled to 1~3℃ is injected into the harvesting pool beforehand. After all the salmon and trout in the breeding pool are transferred to the harvesting pool, the transfer channel is sealed with a pipe plug. Then, ice salt mixture is added to the harvesting pool to lower the water temperature to 0.5~2℃ within 1~2 minutes. Then, the salmon and trout stay in this environment for 3~5 minutes to allow the fish to enter a deep sedation state. (4) Non-destructive capture and transfer: Transfer salmon and trout in a deep sedated state from the capture pool to the transport vehicle.

4. A fishing method for reducing stress damage in salmon and trout according to claim 3, characterized in that, It also includes step (5) gradient recovery: the fish in the transport vehicle are transferred to gradient recovery tanks with water temperatures of 8℃, 12℃ and 16℃ in sequence, and each gradient is maintained for 5 to 10 minutes. After the fish completes the gradient recovery, it regains its ability to swim independently.

5. A method for reducing stress damage in salmon and trout according to claim 3, characterized in that, In step (1), the water temperature of the aquaculture pond is reduced to 12-15℃ at a rate not exceeding 1℃ / day; and the light conditions of the aquaculture pond are reduced to 100-200 lux at a rate not exceeding 50 lux / day.

6. A fishing method for reducing stress damage in salmon and trout according to claim 3, characterized in that, In step (1), feeding is stopped 48-72 hours before harvesting, and the dissolved oxygen level in the aquaculture pond is kept not less than 6 mg / L during the feeding stop.

7. A fishing method for reducing stress damage in salmon and trout according to claim 3, characterized in that, In step (2), the side of the breeding pond closest to the transfer channel is protected from light, and the light intensity is ≤10 lux.

8. A method for reducing stress damage in salmon and trout according to claim 3, characterized in that, In step (3), the ice-salt mixture is made by mixing food-grade crushed ice and food-grade salt in a mass ratio of 3-5:

1.

9. A fishing method for reducing stress damage in salmon and trout according to claim 8, characterized in that, The food-grade salts are food-grade sodium chloride, food-grade potassium chloride, or food-grade magnesium chloride.

10. A method for reducing stress damage in salmon and trout according to claim 3, characterized in that, In step (4), salmon and trout in a deep sedation state are transferred from the fishing pond to a transport vehicle using a variable frequency centrifugal fish suction pump or conveyor belt.

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