A method for large-scale cultivation of naked heterotoca loach catfish fry

Abstract

The application provides a large-scale breeding method of naked heterocercal loach, and the method comprises the following steps: temperature control hatching of a breeding pond, static water temperature rising cultivation, ecological cycle cultivation, and a high-density, fast-growth and healthy-fish-body intensive breeding mode of fry is established, the problem of low survival rate in the breeding process of the naked heterocercal loach is solved, and the breeding scale and the breeding efficiency are effectively improved, and key technical support is provided for large-scale propagation and release.

Description

Technical Field

[0001] This invention relates to a method for large-scale cultivation of seedlings of naked loach, belonging to the field of biotechnology. Background Technology

[0002] The naked loach (Xenophysogobio nudicorpa) is an endemic and important economic fish species mainly distributed in the upper reaches of the Yangtze River, the lower reaches of the Jinsha River, the Min River, and the Yalong River. However, in recent years, due to the impact of human activities, its habitat has gradually shrunk or even disappeared, and its natural reproduction scale has drastically decreased, resulting in a sharp decline in its wild population. In 2000, the naked loach was listed as a key protected fish species in Sichuan Province. Before the start of the ten-year fishing ban in the Yangtze River, wild resources of the naked loach were already extremely difficult to obtain, becoming an occasional species with very scarce fish resources, almost on the verge of extinction. This has delayed the implementation of ex-situ conservation efforts such as artificial breeding and artificial population establishment. Since the start of the ten-year fishing ban in the Yangtze River, the situation has eased slightly, but research on the naked loach remains very limited, mainly focusing on morphological characteristics and population genetics.

[0003] In 2023, the Chinese Sturgeon Research Institute of China Three Gorges Corporation achieved a breakthrough in the artificial breeding technology of *Hemiberlesia nautiloides* and began cultivating its fry. They discovered that *Hemiberlesia nautiloides* fry are highly susceptible to Ichthyophthirius multifiliis (white spot disease) and bacterial diseases in aquaculture environments, leading to mass mortality. Therefore, it is urgent to develop a method for the large-scale cultivation of *Hemiberlesia nautiloides* fry to lay the technical foundation for its large-scale release. Summary of the Invention

[0004] This invention provides a method for large-scale cultivation of naked loach fry. This method can effectively reduce the probability of Ichthyophthirius multifiliis disease and bacterial disease during the cultivation of naked loach fry, improve the survival rate, and facilitate the large-scale release of naked loach fry.

[0005] This invention provides a method for large-scale cultivation of juvenile loach fry, comprising the following steps:

[0006] 1) The fertilized eggs to be hatched were incubated at 18℃ and a water flow rate of 0.15L / min to obtain newly hatched fry;

[0007] 2) The newly hatched fry were cultured in static water with temperature increase in stages. The temperature increase rate was 0.5-1℃ / d when the fry were 1-4 days old, and the temperature was increased to 22℃ and maintained for 6 days. When the fry were 10-25 days old, the temperature increase rate was 0.27-0.4℃ / d, and the temperature was increased to 26-28℃ to obtain juveniles.

[0008] 3) The juvenile fish are transferred to another pond for rearing to obtain release fry;

[0009] The transfer culture treatment includes non-hidden culture and hidden culture.

[0010] The seedling large-scale cultivation method described above further includes a pretreatment process before the incubation treatment, which includes the following steps:

[0011] The fertilized eggs were stirred to obtain fertilized eggs with a diameter of 0.2 cm to be incubated.

[0012] In the above-described method for large-scale seedling cultivation, in step 1), the dissolved oxygen concentration in the incubation water is not less than 6 mg / L, the ammonia nitrogen concentration is <0.5 mg / L, and the nitrite concentration is <0.1 mg / L.

[0013] In the seedling large-scale cultivation method described above, step 1) involves incubation water containing nitrifying bacteria and Bacillus subtilis, with the concentration of nitrifying bacteria being 1.5 x 10⁻⁶. 7 The concentration of Bacillus subtilis is 1.5*10⁻⁶ CFU / L or higher. 7 More than one per liter.

[0014] In the large-scale seedling cultivation method described above, in step 2), 4-10 day old fish fry are fed rotifers, and the density of the rotifers is not less than 10 rotifers / mL; the feeding frequency is 4-5 times / day.

[0015] And / or, feed 10-25 day old fish fry with 400μm-500μm Artemia nauplii larvae at a feeding frequency of 4-5 times / day, wherein the density of Artemia nauplii larvae is 10,000 / L;

[0016] And / or, during the static water warming cultivation, when the average body length of the newly hatched fry is not less than 0.7cm, a flow treatment is carried out with a flow rate of 0.04-0.06m / s, with the flow being generated twice a day at 10-hour intervals, each time for 2 hours, for a period of 10 days.

[0017] In the large-scale seedling cultivation method described above, the stocking density for the non-hidden cultivation is 3000-4000 individuals / m². 3 ;

[0018] And / or, the stocking density for the concealed breeding is 2000-3000 fish / m². 3 ;

[0019] And / or, during the concealed cultivation process, flow is generated twice a day at a flow rate of 0.2 m / s, with a time interval of 10 hours, and each flow generation lasts for 2 hours.

[0020] In the large-scale seedling cultivation method described above, the feed particle size for the transfer culture is 0.32-0.42 mm, and the feed includes mannan oligosaccharides with a mass content of 0.2%-0.3%.

[0021] And / or, the culture water in the transfer pond includes live feed, the density of which is 3-4 organisms / mL.

[0022] In the large-scale seedling cultivation method described above, the ammonia nitrogen concentration in the culture water of the transferred pond is <0.5 mg / L, the nitrite concentration is <0.1 mg / L, and the dissolved oxygen is not less than 6 mg / L.

[0023] In the above-described method for large-scale seedling cultivation, during the non-concealed cultivation stage, the water flow velocity is 0.06~0.08m / s.

[0024] And / or, during the concealed cultivation stage, the water flow rate is 0.09-0.14 m / s.

[0025] In the seedling large-scale cultivation method described above, step 4) further includes seedling transfer treatment before the transfer pond cultivation;

[0026] The seedling transfer process is achieved through a seedling transfer device; the seedling transfer device includes a plastic box and a sieve.

[0027] The plastic box includes two long sides, two short sides and one bottom. The long sides and / or the short sides include a number of holes. The shortest distance between the holes and the bottom is 40-50cm.

[0028] The sieve covers the porous structure.

[0029] The present invention provides a method for large-scale seedling cultivation of *Gnaphalium affineum*, which addresses the biological characteristics, physiological, ecological, and nutritional needs of larvae and juveniles of *Gnaphalium affineum*. This method implements phased cultivation, establishing a high-density, fast-growing, and healthy intensive seedling cultivation model. It solves the problem of low survival rate in the seedling cultivation process, effectively improving the scale and efficiency of seedling cultivation, and providing key technical support for large-scale stock enhancement and release. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the stainless steel chassis structure of the concealment device in another specific embodiment of the present invention;

[0031] Figure 2 This is a cross-sectional structural diagram of the concealment device in another specific embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of the air-propulsion device structure in another specific embodiment of the present invention;

[0033] Figure 4 This is a schematic diagram of the stainless steel frame structure of the air-propulsion device in another specific embodiment of the present invention.

[0034] Figure 5 This is a schematic diagram illustrating a specific example of an ecological cycle system according to a particular embodiment of the present invention;

[0035] Figure 6 This is a schematic cross-sectional view of the ecological treatment pond in a specific embodiment of the present invention.

[0036] Figure 7 This is a schematic diagram of a seedling transfer device in another specific embodiment of the present invention.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1-Aquaculture pond; 2-Ground; 3-Inlet main pipe; 4-Outlet main pipe; 5-Outlet main pipe; 6-Fertilizer fermentation tank; 7-Filter media tank; 8-Ecological pond; 9-Water pump; 10-Insect collection tank; 11-Insect attractant lamp; 12-Timer switch; 13-Ecological treatment tank; 14-Nano oxygenation pipe; 15-Blower; 16-PVC air pipe; 17-Plastic box; 18-20 mesh screen; 19-Filter holes; 20-PVC pipe; 21-P VC pipe; 22-Stainless steel outer mesh; 23-Side mesh fixing support; 24-Stainless steel bottom mesh; 25-Stainless steel frame; 26-Stainless steel inner mesh; 27-PVC station pipe for aquaculture pond; 28-Support leg; 29-Transparent round glass ball with a diameter of 5-8cm; 30-Transparent round glass ball with a diameter of 1.5-2cm; 31-Stainless steel frame; 32-Nano aeration pipe; 33-Four-way air pipe connector; 34-Three-way air pipe connector. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0040] This invention provides a method for large-scale cultivation of juvenile loach fry, comprising the following steps:

[0041] 1) The fertilized eggs to be hatched were incubated at 18℃ and a water flow rate of 0.15L / min to obtain newly hatched fry;

[0042] 2) Newly hatched fry are cultured in static water with temperature increase in stages. The temperature increase rate is 0.5-1℃ / d when the fry are 1-4 days old, and the temperature is increased to 22℃ and maintained for 6 days. When the fry are 10-25 days old, the temperature increase rate is 0.27-0.4℃ / d, and the temperature is increased to 26-28℃ to obtain juveniles.

[0043] 3) Transfer the juvenile fish to another pond for rearing to obtain release fry; the rearing treatment includes non-hidden rearing and hidden rearing.

[0044] In detail, in step 1), the fertilized eggs to be hatched are incubated at 18°C ​​with a water flow rate of 0.15L / min. After 120-130 hours of incubation, newly hatched fry are obtained.

[0045] Existing hatching processes are usually carried out in incubators. After hatching, the newly hatched fry are transferred to rearing ponds. However, the newly hatched fry are prone to injury such as bumps and knocks during the transfer, which can lead to their death. Therefore, in this invention, the hatching process is carried out directly within the rearing unit.

[0046] The present invention does not limit the size and shape of the breeding unit for incubation. In one specific embodiment, the breeding unit is a circular breeding pond with a diameter of 2-4m and a depth of 0.6-0.8m.

[0047] In one specific implementation, to prevent the fertilized eggs to be hatched from sinking to the bottom of the breeding unit and affecting the hatching effect, an aeration and oxygenation device is installed in the breeding unit.

[0048] To ensure effective hatching and increase the success rate, an appropriate hatching density can be controlled, such as 10,000-15,000 seeds / m². 3 .

[0049] In step 2), the newly hatched fry are raised in static water with increasing temperature in stages. The refrigeration equipment and water intake in the rearing unit are turned off, and a heating device is placed in the rearing unit. The temperature increase rate is 0.5-1℃ / d for 1-4 days, and the temperature is raised to 22℃ and maintained for 6 days. The temperature increase rate is 0.27-0.4℃ / d for 10-25 days, and the temperature is raised to 26-28℃ to obtain fry.

[0050] Specifically, the warming rate during the period from 1 to 4 days of age includes, but is not limited to, a range of 0.5℃ / d, 0.6℃ / d, 0.7℃ / d, 0.8℃ / d, 0.9℃ / d, 1.0℃ / d, or any combination thereof; and the warming rate during the period from 10 to 25 days of age includes, but is not limited to, a range of 0.27℃ / d, 0.28℃ / d, 0.30℃ / d, 0.32℃ / d, 0.34℃ / d, 0.36℃ / d, 0.38℃ / d, 0.40℃ / d, or any combination thereof.

[0051] In step 3), the fry are transferred to the second culture unit for pond rearing. In the second culture unit, they are successively reared without hiding and reared with hiding to obtain release seedlings that meet the release standards.

[0052] Among them, "no concealment cultivation" means that there are no concealment devices in the second breeding unit, while "concealment cultivation" means that concealment devices are placed in the second breeding unit.

[0053] This invention does not limit the specific type of concealment device; a suitable concealment device can be designed according to the habits of naked loach.

[0054] In one specific embodiment, the concealment device consists of a stainless steel base and a circular glass sphere. Wherein, Figure 1 This is a schematic diagram of the stainless steel base for the concealed device. Figure 2 This is a cross-sectional structural diagram of the concealment device. The stainless steel base is a concentric circular structure, consisting of support legs 28, side mesh fixing pillars 23, a stainless steel frame 25, a stainless steel bottom mesh 24, an outer stainless steel mesh 22, and an inner stainless steel mesh 26. The support legs 28 are 5-10cm high, the side mesh fixing pillars 23 are 20cm high, the stainless steel frame 25 is circular with a diameter of 0.8-0.9m, and the stainless steel bottom mesh 24 is circular and connected to the stainless steel frame 25, with a mesh size of 0.5cm. The inner stainless steel mesh 26 and the outer stainless steel mesh 22 are rectangular, 20cm high, and are connected and fixed to the side mesh fixing pillars 23. There are two sizes of circular glass spheres: one is a transparent circular glass sphere 29 with a diameter of 5-8cm, and the other is a transparent circular glass sphere 30 with a diameter of 1.5-2cm. Each size of sphere is arranged in two layers.

[0055] The present invention provides a method for large-scale breeding of naked loach fry, which addresses the biological characteristics, physiological, ecological, and nutritional needs of naked loach fry at different developmental stages. The method implements phased breeding of naked loach fry, establishing a high-density, fast-growing, and healthy intensive breeding model. This solves the problem of low survival rate in the later larval stage of naked loach fry breeding, effectively improving the scale and efficiency of fry breeding, and providing key technical support for large-scale stock enhancement and release. The inventors analyzed the results and believe the reasons may be as follows: Firstly, by raising the water temperature during the rearing stage of newly hatched fry, the absorption rate of the yolk sac is accelerated, allowing them to start feeding as soon as possible, which greatly improves the survival rate of fry in the rearing stage. Moreover, by raising the water temperature, not only is the growth rate of the fry increased, but more importantly, the life cycle of Ichthyophthirius multifiliis is shortened, minimizing the time that the trophozoite spends on the fish, thus greatly reducing the damage to the fish. Furthermore, by using the ecosystem to control the Ichthyophthirius multifiliis cysts and larvae in the water, the occurrence of Ichthyophthirius multifiliis disease can be prevented. At the same time, by providing hiding places for the fry, their stress is reduced, and their resistance is enhanced, thereby improving the fry's ability to avoid natural predators and increasing the survival rate after release.

[0056] Furthermore, in one specific embodiment of the present invention, a pretreatment is included before the incubation process, and the pretreatment includes the following steps:

[0057] The fertilized eggs were stirred to obtain fertilized eggs with a diameter of 0.2 cm ready for hatching.

[0058] In detail, after the eggs of naked loach are fertilized, the fertilized eggs are stirred to obtain fertilized eggs with a diameter of 0.2 cm ready for hatching.

[0059] In one specific embodiment, the stirring process is carried out in a device with a diameter of 0.6-0.8 m.

[0060] Stirring not only ensures that fertilized eggs are mixed evenly, reduces aggregation, and promotes uniform hatching, but also further improves the hatching success rate by controlling the egg diameter to a specific size.

[0061] It is understandable that the water quality during the incubation process also has a significant impact on the hatching success rate. Furthermore, in a specific embodiment of the present invention, in step 1), the dissolved oxygen concentration in the incubation water is not less than 6 mg / L, the ammonia nitrogen concentration is <0.5 mg / L, and the nitrite concentration is <0.1 mg / L.

[0062] To ensure that the dissolved oxygen, ammonia nitrogen, and nitrite concentrations in the hatching water remain within the aforementioned ranges, and to prevent water quality deterioration due to the accumulation of egg membranes in the water caused by the fry breaking their membranes during hatching, in one specific embodiment, step 1) includes nitrifying bacteria and Bacillus subtilis in the hatching water, with the nitrifying bacteria concentration being 1.5*10⁻⁶. 7 The concentration of Bacillus subtilis is above 1.5*10⁻⁶ CFU / L. 7 More than one per liter.

[0063] Furthermore, in a specific embodiment of the present invention, in step 2), rotifers are fed to fish fry aged 4-10 days, with a rotifer density of not less than 10 rotifers / mL; the feeding frequency is 4-5 times / day.

[0064] Specifically, newly hatched fry obtain nutrition by absorbing the yolk sac from 1 to 5 days of age. At 4 days of age, they are fed rotifers 4 to 5 times a day, with the rotifer density controlled to be no less than 10 rotifers / mL.

[0065] Feeding rotifers at 4 days old not only provides good palatability for newly hatched fry and a rich source of food, but also helps the fry gradually adapt to external food, stimulates their appetite, reduces stress, and improves their adaptability.

[0066] Fish fry aged 10-25 days were fed Artemia nauplii with a size of 400um-500um at a feeding frequency of 4-5 times / day and an Artemia nauplii density of 10,000 nauplii / L.

[0067] In this invention, the source of the brine shrimp nauplii is not limited. They can be obtained through commercial channels or cultivated by the fish themselves. In one specific embodiment, the brine shrimp nauplii are newly hatched brine shrimp nauplii that have been incubated for 18 hours under conditions of water temperature of 30°C, salinity of 3%, and sufficient light. By controlling the incubation time, it is possible to prevent the brine shrimp from growing too large due to excessive incubation time, which would prevent the fish fry from feeding.

[0068] Feeding fish with Artemia nauplii will not introduce Ichthyophthirius multifiliis cysts and larvae into the rearing pond, greatly reducing the probability of Ichthyophthirius multifiliis outbreaks in fish fry at this stage.

[0069] During the still water warming cultivation, when the average body length of the newly hatched fry is not less than 0.7cm, flow treatment is carried out with a flow rate of 0.04-0.06m / s, flow is carried out twice a day, with an interval of 10 hours, and each flow is carried out for 2 hours, for 10 consecutive days.

[0070] One method of water flow generation is to install a water pump in the aquaculture unit. This water flow generation not only concentrates waste within the aquaculture unit for easy discharge, but also trains the fish fry's swimming ability and improves their predation skills, laying the foundation for subsequent cultivation.

[0071] Furthermore, in one specific embodiment of the present invention, the stocking density for non-hidden breeding is 3000-4000 fish / m². 3 ;

[0072] And / or, the stocking density for concealed breeding is 2000-3000 individuals / m². 3 ;

[0073] And / or, during the concealed cultivation process, flow is generated twice a day at a flow rate of 0.2 m / s, with a time interval of 10 hours, and each flow generation lasts for 2 hours.

[0074] Specifically, the stocking density for unhidden breeding includes, but is not limited to, 3000 fish / m². 3 3200 tails / m 3 3400 tails / m 3 3600 tails / m 3 3800 tails / m 3 4000 tails / m 3 Or a range consisting of any two of them.

[0075] The stocking density for covert breeding includes, but is not limited to, 2000 fish / m². 3 2200 tails / m 3 2400 tails / m3 2600 tails / m 3 2800 tails / m 3 3000 tails / m 3 Or a range consisting of any two of them.

[0076] When the stocking density of both unhidden and hidden culture is within the above range, it not only enables efficient use of space according to different stages, increases growth rate and improves water quality control, but also reduces cultivation costs.

[0077] In one specific embodiment, a pneumatic propulsion device is used to generate flow.

[0078] This invention does not limit the specific type of air-propulsion device. Common air-propulsion devices in the field can be selected, or devices with air-propulsion effects can be independently developed.

[0079] In another specific implementation, such as Figure 3 As shown, the air-push device consists of a nano oxygenation tube 32, a stainless steel disc 31, a four-way air pipe connector 33, and a three-way air pipe connector 34. The stainless steel disc 31 is a concentric circle structure with a diameter of 0.8m. The nano oxygenation tube 32 is wrapped around the stainless steel disc 31 three times. The connectors of the two outermost circles are connected by the four-way air pipe connector 33, and the innermost circle is connected by the three-way air pipe connector 34. Figure 4 This is a schematic diagram of the stainless steel disc structure of the air-pneumatic device.

[0080] Water flow treatment not only promotes the discharge of waste and organic matter in aquaculture units and reduces water pollution, but also encourages fish fry to swim and forage more, which helps to improve their physical strength and swimming ability, reduces stress response, and increases survival rate.

[0081] Furthermore, in one specific embodiment of the present invention, the feed particle size of the transferred culture is 0.32-0.42 mm, and the feed includes mannan oligosaccharides with a mass content of 0.2%-0.3%;

[0082] And / or, the culture water in the transfer pond includes live feed, with a density of 3-4 live feeds / mL.

[0083] Specifically, during the transfer rearing process (including both concealed and non-concealed rearing), the feed particle size includes, but is not limited to, a range of 0.32 mm, 0.34 mm, 0.36 mm, 0.38 mm, 0.40 mm, 0.42 mm, or any combination thereof. Feed within the above particle size range is matched to the juveniles' ingestion capacity, thus providing them with better nutrition.

[0084] The mannan oligosaccharide content per 100g of feed includes, but is not limited to, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, or any combination thereof.

[0085] The addition of mannan oligosaccharides helps enhance the immunity and gut health of fish fry, promotes fry growth, increases feed digestibility and absorption, and further improves the immunity of fish fry.

[0086] This invention does not limit the cultivation rules after the fish are transferred to another pond. The feeding frequency and amount can be adjusted according to the feeding situation of the fish fry. In one specific embodiment, the fish are fed 2-3 times a day, and the amount of feed is 1.2 times the normal amount.

[0087] The present invention does not limit the nutritional composition of the feed after the transfer to the pond for rearing, and can select feeds commonly used in the field.

[0088] This can be achieved by combining the trapping and cultivation of live bait with the transfer and cultivation in different ponds to form a circular aquaculture system, thereby improving the efficiency of aquaculture.

[0089] In one specific implementation, the recirculating aquaculture system is as follows: Figure 5 As shown, it comprises an ecological treatment unit 13, aquaculture unit 1, insect-attracting unit 11, and fertilization unit 6. The ecological treatment unit 13 is a cement pool 100m long, 5m wide, and 1.2m deep, entirely below ground level with its elevation extending 0.3m above ground. Figure 6 As shown, the ecological treatment unit 13 is divided into 6 pools, namely, a fertilization pool, a filter media pool, an ecological pool 8, an insect collection pool, and an insect collection pool. The combined area of ​​the fertilization pool and the filter media pool is the same as that of a single ecological pool 8 and an insect collection pool. The fertilization pool is 5m long, 5m wide, and 1.2m deep; the filter media pool is 15m long, 5m wide, and 1.2m deep; and the ecological pool 8 and the insect collection pool are 20m long, 5m wide, and 1.2m deep.

[0090] The fertilization unit 6 includes a fertilization tank and an aeration device. The aeration device includes a blower 15, a PE pipe, an air valve, a 0.8cm diameter hose, and a nano aeration pipe. The blower 15, PE pipe, air valve, 0.8cm diameter hose, and nano aeration pipe are connected in sequence to form the aeration device.

[0091] The aquaculture unit consists of a water pump (9), an inlet main pipe (3), an outlet main pipe (5), and two-stage series aquaculture ponds. Each two-stage series aquaculture pond is composed of two 1m diameter circular PP (polypropylene) ponds connected by a PVC inlet and outlet pipe system. There are two levels of ponds: the first-stage pond is 1.2m high and 0.6m deep; the second-stage pond is 0.8m high and 0.6m deep. Each pond is supported by a PP board at the bottom. The inlet pipe for the first-stage pond is a 6.3cm diameter PVC pipe, and the outlet pipe for the next-stage pond is a 7.5cm diameter PVC pipe. The outlet pipe for the second-stage pond connects to the outlet main pipe, which in turn connects to the ecological treatment unit. Each pond has a drain pipe at the bottom with a valve, connected to the main drain pipe.

[0092] The bottom of the filter media tank is laid with a stainless steel plate, which is 14.8m long and 4.8m wide, with supporting legs 0.3m high. Biological filter media is placed on the stainless steel plate. The biological filter media consists of ceramic pebbles, biological balls and volcanic rock from top to bottom, with particle sizes of 3cm, 8cm and 15cm respectively. Its function is to remove large particulate suspended solids and purify the water.

[0093] The insect-attracting unit consists of an insect-attracting lamp 11, a timer switch 12, and an insect collection pool. The insect-attracting lamp 11 is a halogen lamp with an illuminance of 200 lx, which is turned on at 8 pm and turned off at 6 am. The food organisms in the water are attracted to the lamp and pumped into the breeding pool for the fish fry to feed on.

[0094] Two weeks before the fish fry are transferred to the new pond for rearing, preparations are made for the cultivation of the water in the ecological treatment unit: Water is added to the fertilization tank to a depth of 80cm, 20kg of feed is poured in, and the aeration and oxygenation device is turned on, stirring three times a day to ensure the feed is fully dissolved in the water. After four days, once the feed has completely dissolved and the water turns a yellowish-brown color, the seed source of microalgae such as Chlorella is introduced into the fertilization tank at a rate of 1000g / m³. 3 Add Bacillus subtilis and Bacillus licheniformis to the fertilized water, along with a compound vitamin preparation at a rate of 600 g / m³. After 5 days of cultivation until the fertilized water turns green, turn on the inlet water of the fertilized water fermentation tank, allowing the fermented fertilized water to slowly overflow into the filter and ecological ponds. After adding the fertilized water, turn on the spray equipment and aeration devices in the ecological ponds. After 8 days of cultivation, when the water in the ecological treatment unit turns green, and the density of all food organisms such as rotifers, cladocerans, and copepods is 1-2 individuals / mL, and the ammonia nitrogen concentration is <0.5 mg / L and the nitrite concentration is <0.1 mg / L, transfer the fish fry into this system for further cultivation.

[0095] Before the fish fry are introduced, the water temperature is controlled at around 26-28℃ by switching on and off the spray equipment. One day before the fish fry are introduced, the water pump system is turned on, and the water inflow to each breeding pond is controlled at 0.5 m3 / h. The purpose of this is to filter and intercept cladocerans, copepods and other prey organisms through the screen of the intermediate station pipe in the breeding pond, and retain the prey organisms in the breeding pond, so that the density of prey organisms in the breeding pond is 3-4 per mL.

[0096] Furthermore, in a specific embodiment of the present invention, the ammonia nitrogen concentration in the culture water of the transferred culture pond is <0.5 mg / L, the nitrite concentration is <0.1 mg / L, and the dissolved oxygen is not less than 6 mg / L.

[0097] Maintaining these water quality indicators within the recommended range helps create a healthy aquaculture environment, thereby promoting the healthy growth and high survival rate of fish fry.

[0098] Furthermore, in one specific embodiment of the present invention, during the non-hidden cultivation stage, the water flow velocity in the aquaculture area is 0.06~0.08m / s;

[0099] And / or, during the concealed cultivation stage, the water flow velocity in the aquaculture area is 0.09-0.14 m / s.

[0100] In detail, during the non-concealed cultivation stage, the water flow velocity for aquaculture includes, but is not limited to, 0.06 m / s, 0.062 m / s, 0.064 m / s, 0.066 m / s, 0.068 m / s, 0.070 m / s, 0.072 m / s, 0.074 m / s, 0.076 m / s, 0.078 m / s, 0.08 m / s, or any combination thereof.

[0101] During the concealed cultivation stage, the water flow velocity for aquaculture includes, but is not limited to, 0.09 m / s, 0.10 m / s, 0.11 m / s, 0.12 m / s, 0.13 m / s, 0.14 m / s, or any combination thereof.

[0102] In another specific embodiment of the present invention, during the first 10 days of the concealed cultivation stage, the water flow rate is 0.09-0.10 m / s, and after the concealed cultivation stage has entered the 10-day period, the water flow rate is 0.11-0.14 m / s.

[0103] When the water flow rate is controlled within the above-mentioned range in stages, the physiological needs and behavioral characteristics of the fish fry at different growth stages are met. These flow rate differences help optimize the environment and improve the health and growth of the fish fry.

[0104] Furthermore, in a specific embodiment of the present invention, step 4) further includes seedling transfer treatment before transferring to the pond for cultivation;

[0105] Transplanting is achieved through a transplanting device; such as Figure 7 As shown, the seedling transfer device includes a plastic box 17 and a sieve 18;

[0106] The plastic box includes two long sides, two short sides and one bottom. The long sides and / or short sides include several perforated structures 19. The shortest distance between the perforated structures 19 and the bottom of the box is 40-50cm.

[0107] The screen has an 18-hole structure.

[0108] During use, the water in the breeding pond is drained to a depth of 30cm. This device is then inserted into the drain pipe outside the breeding pond. The station pipe with the screen in the middle of the breeding pond is pulled out, and the fish fry are carried into the fish fry collection device along the direction of the water flow. When the water in the pond is almost drained, the water inlet of the breeding pond is turned on to the maximum, and the fish fry remaining in the drain pipe are flushed into the fish fry collection device. The device is then lifted, and the fish fry are transferred to the next level of breeding facilities.

[0109] The present invention does not limit the size of the plastic box. A plastic box of appropriate size can be selected according to actual needs. In one specific embodiment, the plastic box is 1-1.5m long, 0.5-1m wide, 0.8-1.0m high, and 0.2-0.3cm thick.

[0110] It is understandable that the number of holes and the spacing between holes on the long and / or short sides of the plastic box can be adjusted according to the actual situation.

[0111] In one specific embodiment, the long side of the plastic box has 20-30 rows of holes with a diameter of 2cm, each row having 5-8 holes with a hole spacing of 2cm, and the short side of the plastic box has 10-20 rows of holes with a diameter of 2cm, each row having 5-8 holes with a hole spacing of 2cm.

[0112] You can choose a suitable screen according to your actual needs, as long as it can ensure that the fish fry are not carried away from the transfer device by the water flow. For example, you can choose a 20-mesh screen.

[0113] To improve the stability of the screen, in one specific method, the holes on the long and short sides of the 20-mesh screen are sealed and fixed to the box with hot melt adhesive. The long side screen is 0.9-1.3m long and 0.3-0.4m wide, and the short side screen is 0.5-0.9m long and 0.3-0.4m wide.

[0114] In another specific implementation, such as Figure 7As shown, the transfer device also includes a PVC pipe 21 and a PVC connector 20. The bottom of the plastic box 17 has a hole structure 19 with a diameter of 110mm in the middle. The PVC pipe 21 has a diameter of 110mm, matching the diameter of the drainage pipe at the bottom of the pond. The PVC connector 20 has a diameter of 110mm, matching the size of the PVC pipe 21. The PVC pipe 21 is connected to the PVC connector 20, secured with PVC glue, and then inserted into the hole at the bottom of the box for further fixation with hot melt glue. Naked loach fry all lie flat on the bottom of the pond. When transferring the fry to another pond for rearing, the fry are all flat on the bottom and less than 1cm in length. Using a net to catch the fry will cause a large number of fry to be injured and die. Using the above-mentioned transfer device can completely avoid this problem, achieving a 100% survival rate.

[0115] The following describes the large-scale seedling cultivation method provided by the present invention through specific embodiments.

[0116] In April 2024, the Wudongde Stocking and Release Station of the Chinese Sturgeon Research Institute of China Three Gorges Corporation used the method provided by this invention to carry out large-scale breeding of naked loach fry, specifically including the following steps:

[0117] 1. Incubation process:

[0118] After fertilization, the eggs are stirred in a 0.6m diameter basin until they reach a diameter of about 0.2cm. Then, the fertilized eggs are transferred to a rearing tank for incubation, with a hatching density of 15,000 eggs / m². 3 A 2m diameter and 0.8m depth rearing tank was selected as the rearing and hatching tank. An aeration and oxygenation device was installed in this tank. Before transferring the fertilized eggs, the water temperature in the rearing tank was adjusted to the same as the spawning water temperature. During hatching, the water temperature was controlled at around 18℃, the inflow rate was 0.15L / min, dissolved oxygen was maintained above 6mg / L, ammonia nitrogen concentration was <0.5mg / L, and nitrite concentration was <0.1mg / L. When the fertilized eggs entered the tailing stage, 300g / m³ of ammonia was added to the rearing tank. 3 Nitrifying bacteria and Bacillus subtilis were added. After 120 hours of incubation, newly hatched fry were obtained.

[0119] 2. Stage-by-stage static water warming cultivation:

[0120] After the newly hatched fry shed their membranes, the refrigeration equipment in the circulation system is turned off, and the water intake to the rearing pond is shut off. A heating device is placed in the rearing pond to slowly raise the water temperature at a rate of 1℃ / day. At 4 days old, the water temperature reaches 22℃ and is maintained at this temperature for 6 days. On the day before the yolk sac is completely absorbed, rotifers are started on the 4th day, fed 4-5 times a day, maintaining a rotifer density of at least 10 rotifers / ml in the pond. When the fry reach 10 days old, Artemia nauplii are started on the 4th day, fed 4-5 times a day. During the 10-25 day rearing stage, the water temperature is gradually increased from 22℃ to 28℃ at a rate of 0.4℃ / day. The Artemia nauplii are newly hatched nauplii that have been incubated for 18 hours under conditions of 30℃ water temperature, 3% salinity, and sufficient light. Once the fry reach a total length of 0.7cm, a water pump is installed in the rearing pond to create flow for 2 hours a day, once in the morning and once in the evening, with the flow rate controlled at 0.04m / s. The water quality is monitored daily, with ammonia nitrogen concentration <0.5mg / L, nitrite concentration <0.1mg / L, and dissolved oxygen maintained above 6mg / L, to obtain juvenile fish.

[0121] 3. Use Figure 7 The transfer device shown is used to transfer juvenile fish. The device consists of a plastic box, a 20-mesh screen, PVC pipes, and PVC connectors. The plastic box is 1m long, 0.5m wide, 0.8m high, and 0.2cm thick, and includes two long sides, two short sides, and a bottom. The long sides have 20 rows of 2cm diameter holes, with 5 holes per row and a 2cm spacing between the holes. The bottom row of holes is 40cm from the bottom. The short sides have 10 rows of 2cm diameter holes, with 5 holes per row and a 2cm spacing between the holes. The bottom row of holes is also 40cm from the bottom. A 110mm diameter hole is drilled in the center of the bottom. The PVC pipes are 110mm diameter, matching the diameter of the drainage pipe at the bottom of the pond. The PVC connectors are also 110mm diameter, matching the size of the PVC pipes. The PVC pipes are connected to the PVC connectors, secured with PVC glue, and then inserted into the hole at the bottom of the box and secured with hot melt glue. Use a 20-mesh sieve to seal the perforated areas on the long and short sides, and fix them to the box with hot melt adhesive. The sieve on the long side is 0.9m long and 0.3m wide, and the sieve on the short side is 0.5m long and 0.3m wide.

[0122] Drain the water in the rearing pond to a depth of 30cm. Insert the fry transfer device into the drain pipe outside the rearing pond. Pull out the central pipe with the screen in the middle of the rearing pond. The fry will be carried into the fry collection device along the direction of the water flow. When the water in the pond is almost drained, turn the water inlet of the rearing pond to the maximum to flush the fry remaining in the drain pipe into the fry collection device. At this time, insert a 40cm long and 110mm diameter PVC pipe into the PVC pipe of the fry collection device to prevent the fry from flowing out from the middle. Then lift the device and transfer the fry to the second rearing unit.

[0123] 4. Transfer to another pond for cultivation

[0124] 1) Construct an ecological cultivation system

[0125] The ecological cultivation system comprises an ecological treatment unit, a breeding unit, an insect-attracting unit, and a fertilization / fermentation unit. The ecological treatment unit is a 100m long, 5m wide, and 1.2m deep cement pool, entirely below ground level with its elevation extending 0.3m above ground. The ecological treatment unit is divided into six pools: a fertilization / fermentation pool, a filter media pool, an ecological pool, another ecological pool, another ecological pool, and an insect collection pool. The combined area of ​​the fertilization / fermentation pool and the filter media pool is the same as that of a single ecological pool or insect collection pool. The fertilization / fermentation pool is 5m long, 5m wide, and 1.2m deep; the filter media pool is 15m long, 5m wide, and 1.2m deep; and the ecological pool and insect collection pool are 20m long, 5m wide, and 1.2m deep.

[0126] The fertilization unit includes a fertilization tank and an aeration device. The aeration device includes a blower, PE pipe, air valve, 0.8cm diameter hose, and nano aeration pipe. The blower, PE pipe, air valve, 0.8cm diameter hose, and nano aeration pipe are connected in sequence to form the aeration device.

[0127] The aquaculture unit consists of a water pump, an inlet main pipe, an outlet main pipe, and two tandem aquaculture tanks. Each tandem aquaculture tank is composed of two 1m diameter circular PP (polypropylene) tanks connected by a PVC inlet and outlet pipe system. There are two levels of tanks: the first level is 1.2m high and 0.6m deep; the second level is 0.8m high and 0.6m deep. Each tank is supported by a PP board at the bottom. The inlet pipe for the first level is a 6.3cm diameter PVC pipe, and the outlet pipe for the next level is a 7.5cm diameter PVC pipe. The outlet pipe for the second level tank connects to the outlet main pipe, which in turn connects to the ecological treatment unit. Each tank has a drain pipe at the bottom with a valve, connected to the main drain pipe.

[0128] The filter tank has a stainless steel plate at the bottom, which is 14.8m long and 4.8m wide, with supporting legs 0.3m high. Biological filter media is placed on the stainless steel plate, consisting of ceramic pebbles, biological balls, and volcanic rock from top to bottom, with particle sizes of 3cm, 8cm, and 15cm respectively. Its function is to remove large suspended solids and purify the water.

[0129] The insect-attracting unit consists of an insect-attracting lamp, a timer switch, and an insect collection pool. The insect-attracting lamp is a halogen lamp with an illuminance of 200 lx, which is turned on at 8 pm and turned off at 6 am. Food organisms in the water are attracted to the lamp and then pumped into the breeding pool for the fish fry to feed on.

[0130] Two weeks before the fish fry are transferred to the fertilization tank, add water to a depth of 80cm in the fertilization tank, pour in 20kg of feed, turn on the aeration device, and stir three times a day to ensure the feed is fully dissolved in the water. After four days, when the feed is completely dissolved and the water turns a yellowish-brown color, introduce microalgae such as Chlorella into the fertilization tank at a rate of 1000g / m³. 3 Add Bacillus subtilis and Bacillus licheniformis to the fertilizer solution at a rate of 600 g / m³. 3 Add compound vitamin preparation to the fertilizer water, and after cultivating for another 5 days until the fertilizer water turns green, turn on the water intake of the fertilizer water fermentation tank, and let the fermented fertilizer water slowly overflow into the filter tank and ecological tank.

[0131] After adding fertilizer and water, turn on the ecological spraying equipment and aeration device. After 8 days of cultivation, the water in the ecological treatment unit turns green, and the density of all food organisms such as rotifers, cladocerans, and copepods is 1-2 per mL, and the ammonia nitrogen concentration in the water is <0.5 mg / L and the nitrite concentration is <0.1 mg / L.

[0132] Before the fish fry are introduced, the water temperature is controlled at around 26-28℃ by switching the sprinkler system on and off. One day before the introduction of the fish fry, the water pump system is turned on, and the water inflow to each rearing pond is controlled at 0.5m³. 3 / h, the purpose of which is to filter and intercept cladocerans, copepods and other prey organisms through the screen of the intermediate station pipe in the aquaculture pond, so as to retain the prey organisms in the aquaculture pond and make the density of prey organisms in the aquaculture pond 3~4 / mL.

[0133] 2) Transfer to a breeding pond

[0134] Unhidden rearing stage: When 26-day-old fry are transferred into the aquaculture system, the stocking density is 3000 fish / m² in each 1m diameter rearing pond. 3 Clean the screen of the intermediate station pipe once a week, feed it twice a day with a particle size of 0.32~0.42mm, and mix 0.2~0.3g of mannan oligosaccharide into every 100g of feed to improve its resistance to Ichthyophthirius multifiliis disease; the feeding amount is 1.2 times the normal feeding amount, and the uneaten feed is discharged into the fertilization tank as raw material for fertilization. This stage of cultivation lasts for 15 days. During this period, the water temperature is controlled at 26-28℃, the ammonia nitrogen concentration is <0.5mg / L, the nitrite concentration is <0.1mg / L, and the dissolved oxygen is maintained above 6mg / L.

[0135] Hidden rearing stage: When the fry reach 41 days of age, they enter the ecological cycle hidden rearing stage. Hidden devices are placed in the rearing pond to provide refuge. An air-pump device is placed below the hidden devices and is activated once a week to backwash the devices, removing accumulated dirt. Additionally, the air-pump device generates a reverse current of 0.2 m / s to train the fry's swimming ability. The stocking density is adjusted to 2000 fry / m² during this stage. 3 Clean the screen of the intermediate station pipe once a week, feed with a particle size of 0.32~0.42mm twice a day, and mix 0.2~0.3g of mannan oligosaccharide into every 100g of feed to improve the disease resistance of Ichthyophthirius multifiliis. The feeding amount is 1.2 times the normal feeding amount. The uneaten feed is discharged into the fertilization tank as raw material for fertilization. This stage is maintained until release to obtain the released seedlings.

[0136] The concealment device consists of a stainless steel base and round glass spheres. The stainless steel base has a concentric circular structure, comprising support legs, side mesh fixing pillars, a stainless steel frame, a stainless steel bottom mesh, an outer stainless steel mesh, and an inner stainless steel mesh. The support legs are 5cm high, the side mesh fixing pillars are 20cm high, the stainless steel frame is circular with a diameter of 0.8m, and the stainless steel bottom mesh is circular and connected to the stainless steel frame with a mesh size of 0.5cm. The inner and outer stainless steel meshes are rectangular, 20cm high, and connected and fixed to the side mesh fixing pillars. Two sizes of round glass spheres are used: one is a 5cm diameter transparent round glass sphere, and the other is a 1.5cm diameter transparent round glass sphere. Each size of sphere is arranged in two layers.

[0137] The air-assisted device consists of a nano-oxygenation tube, a stainless steel disc, a four-way air pipe connector, and a three-way air pipe connector. The stainless steel disc is a concentric circle structure with a diameter of 0.8m. The nano-oxygenation tube is wrapped around the stainless steel disc three times. The outer two rings are connected at the joints with a four-way air pipe connector, and the innermost ring is connected at the joints with a three-way air pipe connector.

[0138] Within 1-15 days after the fish fry are introduced, the water flow velocity in the pond should be controlled at 0.06 m / s by adjusting the water inflow rate and angle. From day 16 to 25 after introduction, the water flow velocity should be controlled at 0.10 m / s. From then until release, the water flow velocity should be controlled at 0.14 m / s. The pond should be sludged 1-2 times daily, and the sludge should be transferred to a fertilization fermentation tank for fermentation. The fertilization fermentation tank should be regularly fertilized with 1000 g / m³ of fertilizer. 3 The fertilized water is infused with Bacillus subtilis and Bacillus licheniformis. The fermented wastewater can serve as a nutrient source for microalgae in the ecological pond. The wastewater in the fertilized water fermentation pond is always fully filled. The amount of wastewater discharged into the pond each day is the amount of fermented fertilized water that overflows into the filter pond and ecological pond, truly achieving zero discharge of circulating water.

[0139] Using the above methods, the Wudongde Breeding and Release Station of the Chinese Sturgeon Research Institute of China Three Gorges Corporation cultivated 50,000 fry of the required size for release in 2024, and released 30,000 of them on June 29, 2024.

[0140] Example 2

[0141] This embodiment is basically the same as the seedling large-scale cultivation method provided in Embodiment 1, except that:

[0142] Step 1) No pretreatment is performed before the incubation process; the fertilized eggs are directly incubated in the breeding pond.

[0143] Example 3

[0144] This embodiment is basically the same as the seedling large-scale cultivation method provided in Embodiment 1, except that:

[0145] In step 1), the dissolved oxygen concentration is 5.5 mg / L.

[0146] The hatching rates of the large-scale seedling cultivation methods provided in Examples 1-3 were statistically analyzed, and the specific results are shown in Table 1.

[0147] Table 1

[0148]

[0149] Example 4

[0150] This embodiment is basically the same as the seedling large-scale cultivation method provided in Embodiment 1, except that:

[0151] In step 2), the rotifer density is 5 rotifers / mL.

[0152] Example 5

[0153] This embodiment is basically the same as the seedling large-scale cultivation method provided in Embodiment 1, except that:

[0154] In step 2), if the body length of the newly hatched fry is not less than 0.7cm, no flow generation is required.

[0155] Example 6

[0156] This embodiment is basically the same as the seedling large-scale cultivation method provided in Embodiment 1, except that:

[0157] In step 4), the stocking density for unhidden rearing is 4500 fish / m². 3 The stocking density for concealed breeding was 3500 fish / m². 3 .

[0158] Example 7

[0159] This embodiment is basically the same as the seedling large-scale cultivation method provided in Embodiment 1, except that:

[0160] In step 4), the feed does not contain mannan oligosaccharides.

[0161] Example 8

[0162] This embodiment is basically the same as the seedling large-scale cultivation method provided in Embodiment 1, except that:

[0163] In step 4), the aquaculture water does not include live feed.

[0164] Example 9

[0165] This embodiment is basically the same as the seedling large-scale cultivation method provided in Embodiment 1, except that:

[0166] In step 4), the water flow velocity during the unconcealed rearing stage is 0.05 m / s.

[0167] Comparative Example 1

[0168] The method for large-scale seedling cultivation provided in this comparative example is basically the same as that in Example 1, except that:

[0169] In step 2), the water temperature is maintained at 22℃ during the period from 1 to 25 days of age.

[0170] Test case

[0171] The fish fry cultured using the methods provided in all embodiments and comparative examples were recorded, and the relevant data are shown in Table 2.

[0172] Table 2

[0173]

[0174] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for large-scale cultivation of juvenile loach fry, characterized in that, Includes the following steps: 1) The fertilized eggs to be hatched were incubated at 18℃ and a water flow rate of 0.15L / min to obtain newly hatched fry; 2) The newly hatched fry were cultured in static water with temperature increase in stages. The temperature increase rate was 0.5-1℃ / d when the fry were 1-4 days old, and the temperature was increased to 22℃ and maintained for 6 days. When the fry were 10-25 days old, the temperature increase rate was 0.27-0.4℃ / d, and the temperature was increased to 26-28℃ to obtain juveniles. 3) The juvenile fish are transferred to another pond for rearing to obtain release fry; The transfer culture treatment includes non-hidden culture and hidden culture; During the static water warming cultivation, when the average body length of the newly hatched fry is not less than 0.7cm, a flow treatment is carried out with a flow rate of 0.04-0.06m / s, with the flow being carried out twice a day at 10-hour intervals, for 2 hours each time, for a period of 10 days. The stocking density for the unhideable rearing was 3000-4000 fish / m². 3 ; The stocking density for the concealed breeding was 2000-3000 fish / m². 3 During the concealed cultivation process, flow was generated twice a day at a flow rate of 0.2 m / s, with a time interval of 10 hours, and each flow generation lasted for 2 hours.

2. The method for large-scale seedling cultivation according to claim 1, characterized in that, The incubation process also includes a pretreatment, which includes the following steps: The fertilized eggs were stirred to obtain fertilized eggs with a diameter of 0.2 cm to be incubated.

3. The method for large-scale seedling cultivation according to claim 1 or 2, characterized in that, In step 1), the dissolved oxygen concentration in the incubation water shall not be less than 6 mg / L, the ammonia nitrogen concentration shall be <0.5 mg / L, and the nitrite concentration shall be <0.1 mg / L.

4. The method for large-scale seedling cultivation according to claim 3, characterized in that, In step 1), the incubation water includes nitrifying bacteria and Bacillus subtilis, and the concentration of the nitrifying bacteria is 1.5%. 10 7 The concentration of Bacillus subtilis is 1.5 spores / L or higher. 10 7 More than one per liter.

5. The method for large-scale seedling cultivation according to claim 1 or 2, characterized in that, In step 2), rotifers are fed to 4-10 day old fish fry, with a rotifer density of not less than 10 rotifers / mL; the feeding frequency is 4-5 times / day. And / or, feed 10-25 day old fish fry with 400-500 μm Artemia nauplii larvae at a feeding frequency of 4-5 times / day, wherein the density of Artemia nauplii larvae is 10,000 / L.

6. The method for large-scale seedling cultivation according to claim 1 or 2, characterized in that, The feed grown in the transfer tank has a particle size of 0.32-0.42 mm and includes mannan oligosaccharides with a mass content of 0.2%-0.3%. And / or, the culture water in the transfer pond includes live feed, the density of which is 3-4 organisms / mL.

7. The method for large-scale seedling cultivation according to claim 6, characterized in that, The aquaculture water in the transfer pond has an ammonia nitrogen concentration of <0.5 mg / L, a nitrite concentration of <0.1 mg / L, and a dissolved oxygen concentration of not less than 6 mg / L.

8. The method for large-scale seedling cultivation according to claim 1 or 2, characterized in that, During the unconcealed cultivation stage, the water flow velocity is 0.06~0.08m / s. And / or, during the concealed cultivation stage, the water flow rate is 0.09-0.14 m / s.

9. The method for large-scale seedling cultivation according to claim 1, characterized in that, In step 4), the process before transferring the seedlings to the pond for cultivation also includes seedling transfer treatment; The seedling transfer process is achieved through a seedling transfer device; the seedling transfer device includes a plastic box and a sieve. The plastic box includes two long sides, two short sides and one bottom. The long sides and / or the short sides include a number of holes. The shortest distance between the holes and the bottom is 40-50cm. The sieve covers the porous structure.

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