A method, system and artificial seawater kit for breeding macrobrachium rosenbergii

Abstract

The present application relates to aquaculture technology and aquatic genetic breeding technology, and particularly relates to a method and system for breeding macrobrachium rosenbergii and an artificial seawater set. The method comprises the following steps: obtaining pretreated water by solid-liquid separation and oxidation disinfection from a freshwater source, adding artificial seawater pre-salt to prepare brine with a salinity of 6.0-10.0 ‰, and culturing macrobrachium rosenbergii stage I nauplii, and performing two-stage ion trajectory control according to the development stage, wherein the relative enrichment of calcium ions is controlled in Z1-Z5 stage, and the relative proportion of potassium ions and magnesium ions is increased from Z6 stage to the stage when the proportion of juvenile shrimp is not less than 70%; meanwhile, the density of chlorella is maintained, and a micro-ecological preparation is added, and the total ammonia nitrogen, nitrite and total number of vibrio are used as threshold values to trigger bypass purification and siphon sewage discharge, so that the daily water exchange amount is not more than 30% of the volume of the breeding water. The present application can improve the stability and out-pool rate of low-salinity breeding, and reduce salt consumption, water exchange amount and salt-containing tail water discharge.

Description

Technical Field

[0001] This invention relates to aquaculture technology and aquatic genetic breeding technology, and particularly to a method, system and artificial seawater assembly for breeding giant freshwater prawns. Background Technology

[0002] The giant freshwater prawn (Macrobrachium rosenbergii) is one of the important freshwater farmed shrimp species in my country, characterized by rapid growth, large size, and high commercial value. A relatively complete breeding, seedling propagation, and aquaculture industry chain has been formed. While giant freshwater prawns are raised in freshwater environments, their larval development and metamorphosis are highly dependent on the osmotic pressure and ionic composition of the water. Traditional large-scale seedling production generally requires a brackish water environment with a certain salinity to stably complete larval development and metamorphosis. For seedling production enterprises inland or far from seawater access, a combination of sea salt / artificial seawater salt and freshwater is typically used to prepare the seedling brine. During the seedling process, water quality is maintained through water exchange, wastewater discharge, disinfection, and microecological regulation. However, the aforementioned traditional models generally suffer from the following prominent problems: First, the consumption of artificial seawater salts is high, resulting in high overall seedling costs; second, the seedling process often requires a large volume of water exchange to maintain ammonia nitrogen, nitrite, and pathogen risks within a controllable range, thus generating a large amount of saline wastewater; third, direct discharge of saline wastewater can easily cause salinization of surrounding water bodies and soil, and may also lead to eutrophication, increasingly constrained by green aquaculture and wastewater treatment requirements; fourth, when the salinity of seedlings is further reduced to decrease salt consumption and emissions, the late metamorphosis stage of larvae is more prone to fluctuations in survival rate, decreased physical condition, or asynchronous development, the root causes of which are often related to ion structure imbalance under low salinity conditions, changes in pathogen pressure, and mismatched water quality control methods. Therefore, the research and engineering application of technologies that can achieve stable high survival rates in seedling production under low salinity conditions, while also reducing wastewater emissions and reusing it, has always been a key focus in the field of giant freshwater prawn seedling production.

[0003] In existing technologies, for the feeding and ecological regulation of giant freshwater prawns during the larval rearing process, relevant patents have proposed using a composite feed system consisting of unicellular algae, Artemia nauplii, and egg custard, combined with water quality improvers and microbial agents for water quality management. For example, Chinese patent document CN104938378A discloses a method for ecological larval rearing of giant freshwater prawns. This method includes steps such as preparing the rearing pond, preparing the rearing water, obtaining larvae, feeding, water quality management, transferring to the pond, and freshwater acclimation. In water quality management, pollution-free water quality improvers and microbial agents are used to regulate water quality. The feed consists of a combination of unicellular algae, Artemia nauplii, and egg custard to improve survival rate and accelerate larval emergence. This type of solution focuses on ecological feed and micro-ecological water conditioning to improve the health and efficiency of seedling cultivation. However, from an engineering application perspective, the seedling brine is still based on brackish water with a certain salinity, and water quality maintenance still relies on water exchange, sewage discharge and external regulation. When aiming to further reduce salinity and significantly reduce salt consumption and saline wastewater discharge, it may still face problems such as late-stage abnormal sensitivity under low-salt conditions, difficulty in stable matching of ion structures, and difficulty in substantially reducing the salinity load of wastewater.

[0004] To improve freshwater adaptability and reduce costs by lowering salinity in seedling rearing, some technologies propose a phased salinity reduction approach. For example, Chinese patent document CN108770742A discloses a high-survival-rate seedling rearing method for giant freshwater prawns. This method describes starting with a low salinity level and gradually reducing it in stages over time during the rearing process, while also adjusting temperature, dissolved oxygen, and feeding regimes to improve larval adaptability to freshwater and reduce costs. While this approach provides a pathway for low-salinity seedling rearing from a salinity trajectory control perspective, it typically emphasizes the management logic of salinity changes over time. It lacks sufficient disclosure regarding the fine-tuning of ion structure under low-salinity conditions (especially the sensitivity of key ion ratios / concentrations during the late metamorphosis stage of larvae), sustainable water quality control strategies under low-water-exchange conditions, and deep desalination and closed-loop reuse of saline wastewater. Therefore, during industrial-scale promotion, survival rate fluctuations may still occur between different batches, different water sources, or different production conditions, and the salt load in the wastewater may still require further process-based emission reduction and treatment measures.

[0005] Furthermore, regarding the treatment and reuse of wastewater from seedling cultivation, existing technologies have also proposed the idea of ​​regenerating wastewater from seedling cultivation and then reusing it for seedling production. For example, Chinese patent document CN101503259B discloses a method for regenerating wastewater from Macrobrachium rosenbergii seedling cultivation. The treatment process includes steps such as wastewater filtration, sedimentation, oxidation disinfection, water storage purification, and magnetization. During the water storage purification stage, salinity is measured. If the salinity is insufficient, sea salt crystals are added to bring the salinity of the regenerated seawater to a certain range before it is used for seedling production. This type of technology can achieve the reuse of seedling water to a certain extent, reduce water replenishment, and alleviate some discharge pressure. However, its core is still to reuse the regenerated water in a higher salinity range, without achieving deep separation and reduction of salt at the mechanism level. For the need to significantly reduce salt discharge and achieve high survival rate seedlings under low salinity targets, the following shortcomings may still exist: First, the regeneration process has limited essential reduction in salt load, making it difficult to reduce the intensity of salinity discharge in the tailwater from the source. Second, direct reuse may lead to ion accumulation or ion ratio shift in multiple batches, affecting stability under low salinity conditions. Third, existing regeneration processes usually lack a synergistic coupling mechanism between the low water exchange water quality control triggered by the ion structure matching threshold during the critical metamorphosis period of larvae, which means that further optimization and integration are still needed under the comprehensive goals of low salinity, low water exchange, and low discharge.

[0006] In summary, while existing giant freshwater prawn (Macrobrachium rosenbergii) breeding technologies have accumulated some experience in areas such as ecological feed feeding, micro-ecological water conditioning, staged salinity reduction, and wastewater reuse, there are still technological gaps and engineering challenges in achieving the comprehensive goals of maintaining stable metamorphosis and high survival rates under low salinity conditions, significantly reducing salt consumption and emissions, and realizing deep desalination and closed-loop reuse of tailwater. On the one hand, under low salinity conditions, the later metamorphosis of larvae is more susceptible to ion structure imbalance. Existing technologies often focus on controlling salinity values ​​or conventional water quality indicators, while neglecting the staged matching and stable control of key ion structures. On the other hand, tailwater reuse technologies are mostly based on conventional purification, making it difficult to simultaneously reduce salt load while ensuring water quality stability and mitigating the risk of ion accumulation during the recycling process. Therefore, there is an urgent need for an artificial seawater formulation and supporting breeding method for low-salinity breeding scenarios. This method should ensure larval development and metamorphosis stability while reducing salt consumption, water exchange volume, and tailwater salinity load, thereby meeting the practical needs of the giant freshwater prawn breeding industry for cost reduction, emission reduction, and green sustainable development. Summary of the Invention

[0007] The technical objective of this invention is to address the problems of existing industrialized breeding of giant freshwater prawns, which relies on high-salinity artificial seawater, consumes large amounts of salt, and results in high pressure from saline wastewater discharge. Furthermore, the invention aims to provide a method, system, and artificial seawater assembly for low-salinity breeding of giant freshwater prawns, which addresses the issues of unstable survival rates due to ion structure imbalance and water quality fluctuations during the later stages of larval metamorphosis in low-salinity breeding environments. This method employs two-stage ion trajectory control in a low-salinity breeding brine of 6.0–10.0‰, combined with algae-bacteria coupling threshold-triggered water control, bypass purification, and reverse osmosis desalination and ion mother liquor reinjection in the wastewater. This achieves stable breeding under low-salinity conditions, reduces water exchange volume, minimizes salt consumption, and reduces saline wastewater discharge.

[0008] Firstly, in order to achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A method for breeding giant freshwater prawns includes the following steps:

[0010] S1, freshwater source water is pretreated by solid-liquid separation and oxidation disinfection to obtain pretreated water;

[0011] S2, add pre-prepared artificial seawater salt to the pretreated water to prepare seedling brine, so that the salinity is 6.0-10.0‰;

[0012] S3, introduce stage I nauplius prawn nauplii into the seedling brine and cultivate them;

[0013] S4. Under the stated salinity, a two-stage ion trajectory control is implemented. In the Z1-Z5 stage, the calcium ion concentration is controlled at 180-260 mg / L, the mass concentration ratio of potassium ions to calcium ions is 0.55-0.85, and the mass concentration ratio of magnesium ions to calcium ions is 1.0-1.6. From Z6 until the proportion of juvenile shrimp is not less than 70%, the calcium ion concentration is controlled at 110-150 mg / L, the mass concentration ratio of potassium ions to calcium ions is 1.25-1.70, and the mass concentration ratio of magnesium ions to calcium ions is 2.0-3.0.

[0014] S5, maintaining the density of unicellular algae at The microecological preparation was added at a rate of 1 / mL. Starting from the 4th day after the seedlings were brooded, sewage was siphoned out, and the daily water exchange was controlled to not exceed 30% of the seedling water volume through bypass purification.

[0015] As a further improvement, in step S1, the oxidation disinfection is ozone disinfection, which makes the oxidation-reduction potential of the effluent 650-750mV and maintains it for 20-40min, and then removes the disinfection residue so that the residual chlorine is not higher than 0.02mg / L;

[0016] And / or, in step S2, the pH of the seedling brine is 7.6 to 8.2, and the alkalinity, calculated as calcium carbonate, is 80 to 120 mg / L; the artificial seawater pre-prepared salt includes sodium chloride, magnesium salt, calcium salt, potassium salt, bicarbonate, and trace element salts.

[0017] As a further improvement, in step S3, the water temperature for cultivation is controlled at 30.5-31.5℃, and the dissolved oxygen is not less than 5.0mg / L; for the first 7 days, Artemia nauplii are fed 4 times a day; from the 8th day onwards, egg custard feed is added to the Artemia nauplii feed, and it is fed 4 times a day. The feed ingredients are disinfected or heat-treated.

[0018] As a further improvement, in step S4, the developmental stage determination of the two-stage ion trajectory control includes: determining the Z1-Z5 stage and the Z6 initial stage based on the morphological characteristics of the larvae, and determining that the proportion of juvenile shrimp is not less than 70% as the end condition of the second stage by random sampling and counting.

[0019] And / or, in step S4, the first stage involves adding calcium salts to enrich calcium ions and making the mass concentration ratio of potassium ions to calcium ions lower than that of natural seawater dilution; the second stage involves adding potassium salts, magnesium salts and / or the ion mother liquor obtained in step S6 to increase the ratio of potassium ions and magnesium ions to calcium ions, so as to reduce the fluctuation of the later metamorphosis survival rate under low salinity conditions.

[0020] As a further improvement, in step S5, the unicellular algae include at least two of Chaetoceros, Brown finger algae, and Chlorella; the microecological preparation includes one or more of photosynthetic bacteria, Bacillus, and lactic acid bacteria.

[0021] And / or, in step S5, when the total ammonia nitrogen is greater than 0.5 mg / L, the nitrite is greater than 0.1 mg / L, or the total number of Vibrio is greater than... At the same time, the bypass purification circuit's processing capacity is increased and the siphon discharge is intensified; the daily processing capacity of the bypass purification circuit is 0.5 to 2.0 times the water volume of the seedling pond per day, and is increased to 1.5 to 3.0 times per day when any condition is triggered.

[0022] As a further improvement, the method also includes step S6, in which the tailwater is treated by solid residue removal, activated carbon adsorption, nano-filter ball filtration and reverse osmosis desalination, and the product water is reused for water distribution or makeup water. The concentrated brine is selectively softened and flocculated and classified with brine to obtain ion mother liquor, which is used for ion replenishment in stage Z6.

[0023] The solid residue removal includes multi-stage screening and filtration, with the final filtration pore size not exceeding 120 mesh; the desalination rate of the reverse osmosis desalination is not less than 95%, and the resulting permeate is reused for the source water makeup in step S1 and / or the salt preparation water in step S2.

[0024] The selective softening flocculation involves adding an alkaline softening agent to concentrated brine to preferentially precipitate calcium ions and separate the solid phase, thereby obtaining softened brine; then, the brine is graded according to conductivity and the concentrations of potassium, calcium, and magnesium ions to obtain an ion mother liquor that meets the requirements for ion trajectory control in the Z6 stage.

[0025] Secondly, the present invention also provides an artificial seawater kit for implementing the method, comprising a basic pre-prepared salt, a first-stage ion compensation pack, and a second-stage ion compensation pack;

[0026] The basic pre-prepared salt is used to prepare freshwater to a salinity of 6.0–10.0‰; the first-stage ion compensation package is used to ensure that the seedling water in stages Z1–Z5 meets the following requirements: calcium ion concentration of 180–260 mg / L, potassium ion to calcium ion mass concentration ratio of 0.55–0.85, and magnesium ion to calcium ion mass concentration ratio of 1.0–1.6; the second-stage ion compensation package is used to ensure that the seedling water from stage Z6 to stage Z5, when the proportion of juvenile shrimp is not less than 70%, meets the following requirements: calcium ion concentration of 110–150 mg / L, potassium ion to calcium ion mass concentration ratio of 1.25–1.70, and magnesium ion to calcium ion mass concentration ratio of 2.0–3.0.

[0027] Preferably, the basic pre-prepared salt includes sodium chloride, magnesium salt, calcium salt, potassium salt, bicarbonate and trace element salt, wherein the trace element salt includes one or more of borate, strontium salt and bromide salt; the second-stage ion compensation package and the ion mother liquor obtained in step S6 can be mutually substituted as sources of potassium and magnesium ions in the second stage at a mass fraction of 10% to 80%.

[0028] Thirdly, the present invention also provides a giant freshwater prawn breeding system for implementing the method, comprising a source water pretreatment unit, a salt preparation unit, a nursery pond unit, an algae and bacteria addition unit, a bypass purification loop, a tailwater reverse osmosis desalination unit, and a concentrated brine softening, grading, and ion mother liquor unit; the source water pretreatment unit is connected to the salt preparation unit, the salt preparation unit is connected to the nursery pond unit, the algae and bacteria addition unit and the bypass purification loop are respectively connected to the nursery pond unit, the tailwater outlet of the nursery pond unit is connected to the tailwater reverse osmosis desalination unit, the product water outlet of the tailwater reverse osmosis desalination unit is connected to the salt preparation unit and / or the source water pretreatment unit, the concentrated brine outlet of the tailwater reverse osmosis desalination unit is connected to the concentrated brine softening, grading, and ion mother liquor unit, and the concentrated brine softening, grading, and ion mother liquor unit is connected to the nursery pond unit to provide a second-stage ion supply to the nursery pond.

[0029] Preferably, the source water pretreatment unit includes a raw water equalization tank, a solid-liquid separation device, an oxidation disinfection device, and a disinfection residue removal device; the salt preparation unit includes a salt dissolving tank, a stirring or circulation device, a salinity detection device, a pH detection device, and an alkalinity adjustment device.

[0030] And / or, the system further includes a detection module and a control module. The detection module is used to detect the salinity, pH, dissolved oxygen, total ammonia nitrogen, nitrite, total number of Vibrio cells, and concentrations of potassium, calcium, and magnesium ions in the seedling water. The control module controls the bypass purification circuit treatment capacity, algae and bacteria dosage, water exchange volume, and ion mother liquor dosage based on the detection results.

[0031] The technical advantages of this invention are as follows: By controlling the salinity of the seedling stage at 6.0–10.0‰, and adopting a relatively calcium-rich first-stage ionic structure in stages Z1–Z5, and a second-stage ionic structure that increases the relative proportion of potassium and magnesium ions from Z6 onwards until the proportion of larvae is not less than 70%, the early molting and calcification needs of giant freshwater prawn larvae and their later metamorphosis osmotic regulation needs are matched, reducing the problems of asynchronous metamorphosis, decreased vitality, and fluctuations in harvest rate under low salinity conditions; by maintaining the density of unicellular algae and adding microecological agents, combined with total ammonia nitrogen, nitrite, and arctic acid... The total bacterial count threshold triggers bypass purification and siphon discharge, maintaining stable seedling water levels and reducing the risk of pathogen fluctuations under conditions where daily water exchange does not exceed 30%. After solid residue removal, activated carbon adsorption, nanofiltration, and reverse osmosis desalination, the effluent is reused for water distribution or makeup. Concentrated brine undergoes selective softening, flocculation, and brine fractionation to produce an ion-rich mother liquor, which is then reused for Z6 stage ion replenishment. This not only improves water resource utilization but also reduces the amount of salt added to fresh artificial seawater and the salt load discharged, while minimizing the risk of calcium hardness accumulation and membrane scaling caused by direct reuse of concentrated brine. Therefore, this invention achieves cost reduction, stable production, water conservation, and emission reduction in seedling production while ensuring the survival rate and vigor of giant freshwater prawns in low salinity breeding. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the giant freshwater prawn breeding system of the present invention.

[0033] Figure 2 This is a schematic diagram of the low-salinity breeding method for giant freshwater prawns according to the present invention.

[0034] Figure 3 This is a schematic diagram of the two-stage ion trajectory control of the present invention.

[0035] Figure 4 This is a schematic diagram of the closed-loop process of tailwater desalination and pollution removal and ion mother liquor reintroduction in this invention.

[0036] Figure 5 Key ion ratio A graph showing how the number of cultivation days changes.

[0037] Figure 6 Key ion ratio A graph showing how the number of cultivation days changes.

[0038] Figure 7 This is a graph showing the change in total ammonia nitrogen (TAN) in the seedling water as a function of the number of days incubation.

[0039] Figure 8 This is a graph (logarithmic scale) showing the change in the total number of Vibrio bacteria in the seedling water as a function of the number of days of cultivation.

[0040] Figure 9 This is a comparison chart of cumulative salt load during the cultivation period.

[0041] Figure 10 This is a comparison graph showing the change in operating flux of a reverse osmosis unit over time. Detailed Implementation

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the following embodiments are used to illustrate the technical solutions of the present invention, and not to limit the scope of protection of the present invention. Equivalent substitutions made by those skilled in the art for various unit devices, salt sources, addition methods, or detection methods without departing from the concept of the present invention should all fall within the scope of protection of the present invention.

[0043] I. Terminology Explanation

[0044] 1. Low salinity seedling brine refers to brackish water prepared by adding artificial seawater pre-prepared salt to pre-treated freshwater source water for the cultivation of giant freshwater prawn larvae. In this invention, the salinity is 6.0 to 10.0‰.

[0045] 2. Two-stage ion trajectory refers to controlling the concentration of calcium ions and the mass concentration ratio of potassium and magnesium ions relative to calcium ions according to the different developmental stages of giant freshwater prawns, while maintaining the salinity of the low-salinity seedling brine at a basically stable level, so that the early molting and calcification stages and the later metamorphosis and osmotic regulation stages obtain matching ion environments respectively.

[0046] 3. The Z1 to Z5 stages refer to the zoea stages of the giant freshwater prawn larvae from the first to the fifth stage, which can be determined by the morphological characteristics of the larvae.

[0047] 4. The stage from Z6 to the point where the proportion of juvenile shrimp is not less than 70% refers to the stage from when the larvae enter the sixth stage of zoea larvae until the proportion of juvenile shrimp in the group reaches more than 70%, which is the key stage of metamorphosis in the later stage of this invention.

[0048] 5. The proportion of juvenile shrimp refers to the percentage of randomly sampled shrimp that have metamorphosed into juvenile shrimp out of the total number of samples.

[0049] 6. Algae-bacteria coupling refers to maintaining a certain density of unicellular algae in the seedling water and adding microecological agents, so that the algae absorb some inorganic nitrogen, stabilize the ecological buffering capacity of the water body, and inhibit opportunistic pathogens through competition with beneficial bacteria.

[0050] 7. Threshold-triggered water control refers to using total ammonia nitrogen, nitrite and total number of Vibrio as trigger indicators. When any of these indicators exceeds the set threshold, the bypass purification circuit's processing capacity is increased first and the siphon discharge is intensified before water replenishment or replacement.

[0051] 8. The bypass purification circuit refers to the circulating treatment branch connected to the seedling pond. The seedling water is pumped to the nano-filter ball bed and / or activated carbon adsorption bed for treatment and then returned to the seedling pond.

[0052] 9. Ion mother liquor refers to the brine obtained after selective softening and flocculation to reduce calcium hardness and brine classification of reverse osmosis concentrated brine. It is used to replenish potassium and magnesium ions from Z6 to the stage where the proportion of larvae is not less than 70%.

[0053] 10. Artificial seawater kit refers to a combination product used to implement the low salinity breeding method of the present invention, including basic pre-prepared salt, a first-stage ion compensation pack and a second-stage ion compensation pack. If necessary, the second-stage ion compensation pack can be partially replaced by ion mother liquor.

[0054] II. System Structure

[0055] like Figure 1 As shown, the low-salinity breeding system for giant freshwater prawns of this invention includes a source water pretreatment unit, a salt preparation unit, a nursery pond unit, an algae and bacteria addition unit, a bypass purification loop, a wastewater reverse osmosis desalination unit, and a concentrated brine softening, grading, and ion-containing mother liquor unit. The units are connected via pipelines, valves, pumps, and a detection and control module to form an integrated system for low-salinity nursery and wastewater reuse.

[0056] The raw water pretreatment unit is used to treat freshwater source water into pretreated water suitable for preparing brine for seedling cultivation. This unit may include a raw water equalization tank, a coarse filtration device, a fine filtration device, an oxidation disinfection device, and a disinfection residue removal device. The coarse filtration device can use a 20-40 mesh screen, and the fine filtration device can use an 80-120 mesh bag filter, sand filter, or disc filter; the oxidation disinfection device is preferably an ozone disinfection device, but a chlorine-containing disinfection device can also be used; the disinfection residue removal device can be an activated carbon column, an aeration degassing device, or a reducing agent dosing device. The outlet of the raw water pretreatment unit is connected to the brine preparation unit.

[0057] The salt preparation unit is used to mix pretreated water with the basic pre-prepared salt, first-stage ion compensation pack, or second-stage ion compensation pack from the artificial seawater system to form a seedling brine with a salinity of 6.0–10.0‰. The salt preparation unit may include a salt dissolving tank, a stirrer, a circulation pump, a salinity detection device, a pH detection device, an alkalinity adjustment device, and a metering dosing device. The basic pre-prepared salt in the artificial seawater system includes sodium chloride, magnesium salts, calcium salts, potassium salts, bicarbonate, and trace element salts. The trace element salts may include one or more of borates, strontium salts, and bromides. The first-stage ion compensation pack uses calcium salts as the main compensation component, while the second-stage ion compensation pack uses potassium and magnesium salts as the main compensation components. The salt preparation unit is connected to the seedling tank unit.

[0058] The nursery unit is used for the cultivation of first-stage nauplius larvae of the giant freshwater prawn. The nursery unit can be a cement tank, fiberglass tank, or other containers suitable for factory-scale seedling production, and is equipped with aeration pipelines, microporous aeration discs, heating or heat exchange devices, water level control devices, and bottom drain outlets. The nursery unit is connected to the algae and bacteria addition unit, the bypass purification loop, and the wastewater reverse osmosis desalination unit.

[0059] The algae and bacteria addition unit is used to add unicellular algae and microecological preparations to the seedling pond. The unicellular algae may include at least two of Chaetoceros, Brown's Finger Algae, and Chlorella; the microecological preparations may include one or more of photosynthetic bacteria, Bacillus, and lactic acid bacteria. The algae and bacteria addition unit may include a unicellular algae culture tank, a lighting device, an aeration device, an algae solution metering pump, a microecological preparation dissolving tank, and a metering and dosing pump.

[0060] The bypass purification loop is used to circulate and purify the seedling water without extensive water exchange. The bypass purification loop may include a circulation pump, a nano-filter bed, an activated carbon adsorption bed, a flow meter, and a return pipeline. Both the inlet and outlet of the bypass purification loop are connected to the seedling tank unit. Under normal operation, the daily treatment capacity is 0.5 to 2.0 times the volume of the seedling tank water, increasing to 1.5 to 3.0 times the volume per day when a water quality threshold is triggered.

[0061] The tailwater reverse osmosis desalination unit is used to treat siphon discharge wastewater and exchange effluent. This unit includes a tailwater collection tank, a multi-stage screening and filtration device, an activated carbon adsorption device, a nano-filter ball filtration device, a reverse osmosis membrane module, a high-pressure pump, permeate piping, and concentrated brine piping. The permeate piping is connected to the source water pretreatment unit and / or the brine preparation unit, and the permeate can be used for makeup water or brine preparation. The concentrated brine piping is connected to the concentrated brine softening and grading unit and the mother liquor unit.

[0062] The concentrated brine softening and grading unit, along with the ion-concentrated mother liquor unit, is used to further convert reverse osmosis concentrated brine into an ion-concentrated mother liquor suitable for Z6 stage ion replenishment. This unit may include a softening reaction tank, an alkaline softener dosing device, a flocculant dosing device, a sedimentation or filtration device, a brine grading tank, an ion detection device, and an ion-concentrated mother liquor storage tank. The ion-concentrated mother liquor storage tank is connected to the seedling tank unit or the salt preparation unit via a metering pump.

[0063] The detection and control module is used to detect salinity, pH, dissolved oxygen, total ammonia nitrogen, nitrite, total number of Vibrio, and concentrations of potassium, calcium, and magnesium ions. Based on the detection results, it controls the bypass purification circuit's processing capacity, algae and bacteria dosage, water exchange rate, and ion mother liquor dosage.

[0064] III. Specific Technical Route for Implementing the Method of the Invention

[0065] like Figure 2 As shown, the method of the present invention includes S1 to S6. S1 is used to obtain pretreated water with low pathogens and low suspended solids; S2 is used to prepare low salinity seedling brine with a salinity of 6.0 to 10.0‰; S3 is used to complete the first-stage nauplius seedling placement and basic cultivation; S4 matches the ion requirements of different developmental stages through two-stage ion trajectory control; S5 reduces the water exchange volume and stabilizes the water quality through algae-bacteria coupling, bypass purification, and threshold-triggered water control; S6 achieves tailwater desalination and critical period ion replenishment through tailwater reverse osmosis desalination, permeate reuse, and concentrated brine mother liquor production.

[0066] IV. Specific Implementation Methods for Each Step

[0067] (a) Step S1: Raw water pretreatment

[0068] After entering the raw water equalization tank, the freshwater first undergoes settling, grit removal, or coarse filtration to remove large particulate impurities, followed by fine filtration to remove suspended particles. The solid-liquid separated raw water then enters an oxidation disinfection unit. Ozone disinfection is preferred, maintaining the effluent oxidation-reduction potential at 650–750 mV for 20–40 minutes; chlorine-containing disinfectants can also be used. After disinfection, residual oxidant should be removed to ensure residual chlorine does not exceed 0.02 mg / L, avoiding adverse effects on giant freshwater prawn larvae, single-celled algae, and microecological preparations. The pretreated water then enters the salt preparation unit for later use.

[0069] The purpose of this step is to reduce the risk of suspended solids, organic matter, and pathogens entering the source water, laying the foundation for subsequent low-volume water exchange operations where the daily water exchange volume does not exceed 30% of the seedling water volume. If the source water has high turbidity, sand filtration or disc filtration can be added; if the source water has a high organic load, activated carbon pretreatment or ozone contact time can be extended.

[0070] (II) Step S2: Preparation of low-salinity seedling saline solution

[0071] Add basic pre-prepared salt to the pretreated water, and after stirring or circulating to dissolve, prepare a seedling brine with a salinity of 6.0–10.0‰. The salinity can be selected according to different production conditions, preferably 8.0–9.0‰. The pH of the seedling brine should be controlled at 7.6–8.2, and the alkalinity, calculated as calcium carbonate, should be controlled at 80–120 mg / L. After preparation, it is advisable to aerate and mature the brine for 2–12 hours to ensure that the salts are fully dissolved and the pH is stable.

[0072] The basic pre-prepared salt may include sodium chloride, magnesium chloride, magnesium sulfate, calcium chloride, potassium chloride, sodium bicarbonate, and trace element salts such as borates, strontium salts, and bromides. The first-stage ion compensation pack is mainly used to increase the relative content of calcium ions, and the second-stage ion compensation pack is mainly used to increase the relative content of potassium and magnesium ions. In actual preparation, it is not required to accurately reach the ion windows of both stages in one go. Instead, a low-salinity seedling brine is prepared first, and then the concentrations and ratios of potassium, calcium, and magnesium ions are gradually adjusted in S4 according to the developmental stage.

[0073] The amount of salt to be added can be calculated based on the difference between the target ion concentration and the measured ion concentration:

[0074] ;

[0075] in, The required amount of salt to be added; The target ion concentration; This represents the measured ion concentration. This refers to the volume of water used for seedling cultivation. This represents the mass fraction of the target ion in the selected salt. This represents the effective purity of the salt. This formula is used to calculate the dosage of calcium, potassium, or magnesium salts.

[0076] (III) Step S3: Infant Care and Basic Nurturing

[0077] Select healthy, vigorous macrophage stage I nauplii and release them into the nursery brine. Maintain the rearing water temperature at 30.5–31.5℃ and dissolved oxygen at no less than 5.0 mg / L. The nursery pond should be continuously aerated to prevent oxygen deficiency and water stratification. Feed the nauplii of Artemia spp. four times daily for the first seven days; from the eighth day onwards, supplement with egg custard feed, feeding four times daily. Sterilize or heat-treat Artemia hatching equipment, egg custard feed, and feeding tools to reduce pathogen introduction.

[0078] After the larvae emerge, record the water temperature, salinity, pH, dissolved oxygen, feeding status, molting status, and larval activity daily. Starting from the 4th day after the larvae emerge, begin gentle siphoning to remove uneaten food, feces, and molting debris to prevent the accumulation of organic load.

[0079] (iv) Step S4: Two-stage ion trajectory control

[0080] like Figure 3 As shown, this invention divides the larval development process into two ion-controlled stages. The first stage is Z1 to Z5, and the second stage is from Z6 until the proportion of larvae is not less than 70%. Stage determination is completed through larval morphological observation. 50 to 100 larvae are randomly sampled daily, and their developmental stages are observed under a stereomicroscope. When larvae with Z6 characteristics appear in the sample and the production set proportion is reached, the control is switched to the second stage; when the proportion of larvae is not less than 70%, the second stage ends and the process enters freshwater acclimation or hatching management.

[0081] The percentage of baby shrimp can be calculated using the following formula:

[0082] ;

[0083] in, The percentage of baby shrimp; This represents the number of juvenile shrimp in the sample. This represents the total number of samples.

[0084] The control targets for the first stage are: a calcium ion concentration of 180–260 mg / L, a potassium ion to calcium ion mass concentration ratio of 0.55–0.85, and a magnesium ion to calcium ion mass concentration ratio of 1.0–1.6. This stage aims to meet the needs of frequent molting and exoskeleton calcification in early larvae through relative calcium ion enrichment, while ensuring that the potassium ion to calcium ion mass concentration ratio is lower than the natural seawater dilution ratio, thus avoiding excessive potassium supplementation in the early stages and subsequent ion balance imbalance.

[0085] The control targets for the second stage are: a calcium ion concentration of 110–150 mg / L, a potassium-to-calcium ion mass concentration ratio of 1.25–1.70, and a magnesium-to-calcium ion mass concentration ratio of 2.0–3.0. This stage aims to increase the ratio of potassium and magnesium ions relative to calcium ions to match the needs of metamorphosis and osmotic regulation in the later stages of larval development, thereby reducing fluctuations in survival rates during the later stages of metamorphosis under low salinity conditions. The potassium and magnesium ions in the second stage can be sourced from the second-stage ion compensation package, or partially or entirely from the ion mother liquor obtained from S6.

[0086] The ion ratio can be calculated using the following formula:

[0087] ;

[0088] in, This represents the mass concentration ratio of potassium ions to calcium ions. This represents the mass concentration of potassium ions. This represents the mass concentration of calcium ions.

[0089] ;

[0090] in, This represents the mass concentration ratio of magnesium ions to calcium ions. This represents the mass concentration of magnesium ions. This represents the mass concentration of calcium ions.

[0091] In actual production, potassium, calcium, and magnesium ion concentrations can be tested once daily, increasing to twice daily in the second stage. If calcium ion concentrations are below the target range in the first stage, calcium chloride or other soluble calcium salts should be added. If the potassium-to-calcium ion mass concentration ratio is too high, calcium should be added preferentially over potassium. If the magnesium-to-calcium ion mass concentration ratio is too low, magnesium salts should be added. In the second stage, ion stock solution or a second-stage ion compensation pack should be added preferentially to increase the relative ratio of potassium and magnesium ions, and the calcium ion concentration should be controlled to not exceed 150 mg / L.

[0092] Figure 5 The results show that the mass concentration ratio of potassium ions to calcium ions in the present invention group was lower than that of the conventional ratio in the control group in the first stage, and rose to the range of 1.25 to 1.70 in the second stage, forming a trajectory of "low potassium-calcium ratio in the early stage and high potassium-calcium ratio in the later stage". Figure 6 The results show that the mass concentration ratio of magnesium ions to calcium ions in the present invention is maintained at 1.0 to 1.6 in the first stage and adjusted to 2.0 to 3.0 in the second stage, indicating that the present invention can establish different ion structures according to the developmental stage, rather than using a fixed seawater dilution ratio.

[0093] (V) Step S5: Algae-bacteria coupling and threshold-triggered low water exchange

[0094] During the cultivation process, unicellular algae are added to the seedling pond to maintain the density of unicellular algae at a certain level. Single-celled algae per mL. Preferably, they include at least two of Chaetoceros, Browniana triangularis, and Chlorella. Single-celled algae can absorb some inorganic nitrogen in the water, buffer pH fluctuations, and provide some nutrition and feeding stimulation for larvae.

[0095] Simultaneously, a microecological preparation is added, which may include one or more of photosynthetic bacteria, Bacillus, and lactic acid bacteria. The microecological preparation can be added every 2-3 days, or dynamically adjusted according to water quality indicators and the total number of Vibrio bacteria. Through the coupling effect of algae and beneficial bacteria, the proliferation of opportunistic pathogens such as Vibrio is inhibited, reducing the risk of disease during low-salinity seedling cultivation.

[0096] This invention employs threshold-triggered water control. Water quality is controlled when total ammonia nitrogen exceeds 0.5 mg / L, nitrite exceeds 0.1 mg / L, or the total Vibrio count exceeds [a threshold value missing]. When the concentration reaches CFU / mL, increase the bypass purification loop's treatment capacity and intensify siphon drainage. The normal daily treatment capacity of the bypass purification loop is 0.5–2.0 times the volume of the seedling pond water per day, increasing it to 1.5–3.0 times per day after the threshold is triggered. Once the threshold is restored, replenish water or perform a small water change, ensuring that the daily water change does not exceed 30% of the seedling pond water volume.

[0097] Figure 7 The results show that, under the low water exchange conditions of this invention, the total ammonia nitrogen remains below the threshold of 0.5 mg / L, indicating that algae-bacteria coupling, bypass purification, and siphon discharge can replace part of the water quality control function of traditional large-ratio water exchange. Figure 8 The results showed that the total number of Vibrio bacteria in the present invention group was lower than that in the control group, and remained at a lower level for most of the time. The presence of CFU / mL near or below the threshold indicates that algal-bacterial coupling and threshold-triggered water control can reduce the risk of pathogen fluctuations in low-salt seedling cultivation.

[0098] (vi) Step S6: Closed-loop reuse of tailwater and preparation of ion mother liquor

[0099] like Figure 4 As shown, the siphon wastewater and water exchange tailwater generated during the seedling cultivation process enter the tailwater collection tank, where they first undergo multi-stage screening and filtration to remove solid residues such as uneaten feed, feces, and molted shell fragments. The final stage filter has a pore size of no more than 120 mesh to reduce the risk of subsequent reverse osmosis membrane clogging. The filtered tailwater then passes through activated carbon adsorption and nanofiber filtration. Activated carbon adsorption removes some dissolved organic matter, color, and residual oxidation byproducts, while nanofiber filtration retains fine particles and reduces the biodegradable organic load.

[0100] The pretreated effluent enters the reverse osmosis desalination unit, with a desalination rate of no less than 95%. The reverse osmosis permeate is reused as makeup water for S1 and / or as brine for S2, thereby reducing fresh water consumption and effluent discharge. The concentrated brine produced by reverse osmosis enters the concentrated brine softening and fractionation and mother liquor unit.

[0101] Direct reuse of concentrated brine can lead to problems such as excessive calcium hardness, scaling in the reverse osmosis system, and unstable ion ratios. Therefore, this invention selectively softens and flocculates concentrated brine. Specifically, alkaline softening agents such as sodium carbonate, sodium hydroxide, and lime milk are added to the concentrated brine, causing calcium ions to preferentially precipitate. The solid phase is then separated by sedimentation or filtration to obtain softened brine. Subsequently, the brine is graded based on conductivity and the concentrations of potassium, calcium, and magnesium ions. The portion that meets the requirements for ion trajectory control in the second stage is used as the ion mother liquor. After passing testing, the ion mother liquor is stored and metered for addition to the nursery pond from stage Z6 until the proportion of juvenile shrimp is not less than 70%.

[0102] The reverse osmosis desalination rate can be calculated using the following formula:

[0103] ;

[0104] in, This refers to the reverse osmosis desalination rate; The concentration is calculated based on the salinity or conductivity of the reverse osmosis feed water. This refers to the concentration calculated from the salinity or conductivity of the reverse osmosis permeate.

[0105] Figure 9 The invention demonstrates that by reducing salinity, decreasing daily water exchange volume, and reusing produced water, the cumulative salt load during the cultivation period can be significantly reduced. Figure 10 The results show that when the concentrated brine after selective softening flocculation and brine classification is used for the preparation of ion mother liquor, the flux of the reverse osmosis system decreases more slowly; the flux of the comparative example that is directly reused without softening decreases more rapidly, indicating that the concentrated brine mother liquor treatment of the present invention can reduce the risk of scaling and improve system stability.

[0106] V. Examples and Comparative Examples

[0107] The following examples are used to further illustrate the technical effects of the present invention. Unless otherwise specified, all groups used the same water temperature, dissolved oxygen, feeding regime, and daily management conditions. Experimental data are expressed as mean ± standard deviation, and percentage data are calculated according to the corresponding formula.

[0108] (a) Detection methods

[0109] Salinity was measured using a salinity meter; pH and dissolved oxygen were measured using a portable water quality meter; total ammonia nitrogen and nitrite were measured using spectrophotometry; total Vibrio count was counted using TCBS selective medium; unicellular algal density was counted using a hemocytometer; potassium, calcium, and magnesium ions were measured using ion chromatography, ICP, or titration; and reverse osmosis flux was obtained by converting permeate flow rate and membrane area.

[0110] The discharge rate is calculated using the following formula:

[0111] ;

[0112] in, The discharge rate; This refers to the number of baby shrimp harvested from the pond. This refers to the number of juveniles released.

[0113] The cumulative salt load is estimated using the following formula:

[0114] ;

[0115] in, For cumulative salt load; The drainage volume needs to be changed daily; This refers to the salt concentration calculated based on the salinity of the corresponding water body.

[0116] (II) Example 1: Laboratory Low-Salinity Breeding Verification

[0117] This embodiment uses 160L plastic tanks to verify low-salinity breeding. 17,200 stage I nauplius prawns were stocked in each tank, and the water temperature was controlled at 31±0.5℃. For the first 7 days, the prawns were fed brine shrimp nauplius four times daily; from the 8th day onwards, egg custard feed was added four times daily. Wastewater was siphoned out starting from the 4th day.

[0118] Example 1 uses the method of the present invention, with a salinity of 8.5‰, and is executed. Figure 3 The two-segment ion trajectory is shown, and according to... Figure 4 The process shown treats the wastewater, with reverse osmosis permeate reused for makeup water. Concentrated brine undergoes selective softening and flocculation, and is fractionated with brine to form an ion-exchange mother liquor, which is then used for the second-stage makeup water supply. Comparative Example 1 uses conventional 15‰ high-salt seedling cultivation, without two-stage ion trajectory control, with approximately 50% water exchanged daily, and no wastewater is reused via reverse osmosis. Comparative Example 2 uses 8.5‰ low-salt seedling cultivation, but without two-stage ion trajectory control, with approximately 50% water exchanged daily, and no ion-exchange mother liquor is added back.

[0119] Table 1 Comparison of seedling emergence and specifications in laboratory bucket trials

[0120]

[0121] Calculations showed that the survival rate of Example 1 was 14950 / 17200×100%, approximately 86.9%; Comparative Example 1 was 11600 / 17200×100%, approximately 67.4%; and Comparative Example 2 was 12800 / 17200×100%, approximately 74.4%. Example 1 showed an improvement of 19.5 percentage points compared to Comparative Example 1 and 12.5 percentage points compared to Comparative Example 2. These results indicate that under the same low salinity conditions, simply reducing salinity is insufficient to achieve a stable high survival rate. The two-stage ion trajectory method and the re-injection of the mother liquor from the tailwater significantly improve the stability of low-salinity breeding.

[0122] Table 2 Comparison of water and salt consumption

[0123]

[0124] In Table 2, the salt load reduction rate of Example 1 relative to Comparative Example 1 is:

[0125] ;

[0126] in, Salt load reduction rate; The cumulative salt load for Comparative Example 1; The cumulative salt load for Example 1 is calculated. Substituting the data from Table 2, the reduction rate is approximately 66.3%. The salt load reduction rate of Example 1 relative to Comparative Example 2 is approximately 40.7%. The above results are consistent with... Figure 9 The cumulative salt load comparison shown is consistent.

[0127] (III) Example 2: Production Pool Test

[0128] This embodiment uses cement seedling trays for production verification. The area of ​​the seedling trays is... Giant freshwater prawns (Macrobrachium rosenbergii) were released, with a larval density of approximately 118,500 larvae per day. The cultivation period is 18-21 days. The water temperature, water level, aeration and feeding methods are the same for all groups. The difference is that Example 2 uses the low salinity breeding method and two-stage ion trajectory control of the present invention, while the control group uses the conventional salinity seedling cultivation method.

[0129] Table 3 Key Indicators for Productive Pool Trials

[0130]

[0131] According to calculations, the salinity decreased by the following amount:

[0132] ;

[0133] in, This represents the decrease in salinity. The average salinity of the control group; The average salinity is shown in Table 3 for Example 2. According to Table 3, the salinity decreased from 12.65‰ to 8.28‰, a reduction of approximately 34.55%.

[0134] The relative increase in the effluent rate is as follows:

[0135] ;

[0136] in, This represents the relative increase in the discharge rate. The average effluent rate in Example 2; The average leaching rate for the control group is shown in Table 3. According to Table 3, the leaching rate increased from 69.56% to 78.86%, an increase of 9.30 percentage points, representing a relative increase of approximately 13.37%. This result indicates that the present invention can still achieve a higher leaching rate under conditions of approximately one-third lower salinity than conventional methods, demonstrating... Figure 3 The two-segment ion trajectory shown Figure 7 The low water exchange ammonia nitrogen control and Figure 8 The control of Vibrio shown exhibits a synergistic effect.

[0137] (iv) Example 3: Verification of reverse osmosis desalination and preparation of mother liquor for tailwater

[0138] This embodiment adopts Figure 4The wastewater treatment process is shown below. The wastewater undergoes multi-stage screening and filtration, activated carbon adsorption, nano-filter filtration, and reverse osmosis desalination. Reverse osmosis permeate is reused for distribution or makeup water, while concentrated brine enters the selective softening and flocculation unit. An alkaline softening agent is added to preferentially precipitate calcium ions. After solid phase separation, the brine is graded according to conductivity and ion concentration to obtain a mother liquor suitable for the second-stage ion replenishment.

[0139] Table 4 Comparison of water quality before and after effluent treatment.

[0140]

[0141] Calculations show that the salinity removal rate is (8.3-0.18) / 8.3×100%, approximately 97.83%; the total nitrogen removal rate is (24.5-1.8) / 24.5×100%, approximately 92.65%; the total phosphorus removal rate is (2.9-0.10) / 2.9×100%, approximately 96.55%; and the COD removal rate is (182-14) / 182×100%, approximately 92.31%. These data indicate that reverse osmosis desalination can significantly reduce salinity, as well as the loads of nitrogen, phosphorus, and organic pollutants.

[0142] After selective softening flocculation and brine fractionation, the calcium ion hardness in the mother liquor decreased, while the concentrations of potassium and magnesium ions remained relatively high. Using this mother liquor for the second-stage replenishment can reduce the amount of fresh potassium and magnesium salts used, and maintain the potassium-to-calcium ion mass concentration ratio at 1.25–1.70 and the magnesium-to-calcium ion mass concentration ratio at 2.0–3.0 from stage Z6 until the shrimp larvae comprise at least 70% of the population.

[0143] (v) Comparative Example 3: Concentrated brine was reused directly without softening and grading.

[0144] The wastewater treatment process of Comparative Example 3 and Example 3 is basically the same, except that selective softening flocculation and brine classification are omitted, and the reverse osmosis concentrated brine is directly used as feed water. The results show that the calcium hardness in the concentrated brine is high, and after direct feed, the ion ratio in the second stage is not easy to stably enter the target window, and the membrane flux decay is significantly accelerated during reverse osmosis operation.

[0145] like Figure 10 As shown, after selective softening flocculation and brine classification treatment, the reverse osmosis flux of this invention is increased from the initial approximately It dropped to about the 10th day. The flux retention rate was approximately 82.9%; in Comparative Example 3, no softening stage was performed, and the flux decreased from approximately Decrease to approximately The flux retention rate was approximately 54.3%. This result indicates that selective softening flocculation and brine fractionation not only provide ionic mother liquor for the second stage, but also reduce the risk of scaling and improve the operational stability of the wastewater reuse system.

[0146] As shown in Example 1, under low salinity conditions of 8.5‰, this invention achieves a pond discharge rate of 86.9±2.2% through two-stage ion trajectory, algae-bacteria coupling threshold water control, and closed-loop effluent reuse, which is significantly higher than the conventional high-salt control and the low-salt no-trajectory control. As shown in Example 2, in a production nursery, this invention reduces the average salinity from 12.65‰ to 8.28‰, a reduction of approximately 34.55%, while simultaneously increasing the pond discharge rate from 69.56% to 78.86%, an increase of 9.30 percentage points. As shown in Example 3 and Comparative Example 3, the permeate after reverse osmosis desalination can be reused for water distribution or makeup water. The concentrated brine, after selective softening flocculation and brine classification, can be used as the second-stage ion mother liquor for reinjection, reducing both fresh salt consumption and the risk of membrane scaling.

[0147] Therefore, compared to conventional high-salinity seedling raising methods and simple low-salinity seedling raising methods, this invention can stabilize the late-stage metamorphosis of larvae under low salinity conditions, improving the hatching rate and the vitality of larvae; compared to simple water exchange and control methods, it can maintain controllable risks of total ammonia nitrogen, nitrite, and Vibrio while maintaining a daily water exchange rate of no more than 30%; compared to conventional tailwater regeneration methods, it can achieve a closed-loop water-salt system through reverse osmosis permeate reuse and concentrated brine ionization. These technical effects collectively demonstrate that this invention can meet the practical needs of cost reduction, stable production, and emission reduction in low-salinity industrialized breeding of Macrobrachium rosenbergii.

Claims

1. A method for breeding giant freshwater prawns, characterized in that, Includes the following steps: S1, freshwater source water is pretreated by solid-liquid separation and oxidation disinfection; S2, add pre-prepared artificial seawater salt to the pretreated water to prepare seedling brine, so that the salinity is 6.0-10.0‰; S3, introduce stage I nauplius prawn nauplii into the seedling brine and cultivate them; S4. Under the stated salinity, a two-stage ion trajectory control is implemented. In the Z1-Z5 stage, the calcium ion concentration is controlled at 180-260 mg / L, the mass concentration ratio of potassium ions to calcium ions is 0.55-0.85, and the mass concentration ratio of magnesium ions to calcium ions is 1.0-1.

6. From Z6 until the proportion of juvenile shrimp is not less than 70%, the calcium ion concentration is controlled at 110-150 mg / L, the mass concentration ratio of potassium ions to calcium ions is 1.25-1.70, and the mass concentration ratio of magnesium ions to calcium ions is 2.0-3.

0. S5, maintain the density of unicellular algae at 0.8 × 10⁻⁶. 5 ~1.6×10 5 The microecological preparation was added at a rate of 1 / mL. Starting from the 4th day after the seedlings were brooded, sewage was siphoned out, and the daily water exchange was controlled to not exceed 30% of the seedling water volume through bypass purification. The two-stage ion trajectory refers to controlling the calcium ion concentration and the mass concentration ratio of potassium and magnesium ions relative to calcium ions according to the different developmental stages of giant freshwater prawns, while maintaining the salinity of the low-salinity seedling brine at a basically stable level, so that the early molting and calcification stages and the later metamorphosis and osmotic regulation stages obtain matching ion environments respectively.

2. The method according to claim 1, characterized in that, In step S1, the oxidation disinfection is ozone disinfection, which raises the oxidation-reduction potential of the effluent to 650-750mV and maintains it for 20-40 minutes, and then removes disinfection residue.

3. The method according to claim 1, characterized in that, In step S2, the pH of the seedling brine is 7.6-8.2, and the alkalinity, calculated as calcium carbonate, is 80-120 mg / L; the artificial seawater pre-prepared salt includes sodium chloride, magnesium salt, calcium salt, potassium salt, bicarbonate, and trace element salts.

4. The method according to claim 1, characterized in that, In step S3, the water temperature for cultivation is controlled at 30.5-31.5℃, and the dissolved oxygen is not less than 5.0mg / L. For the first 7 days, Artemia nauplii are fed 4 times a day. From the 8th day onwards, egg custard feed is added to the Artemia nauplii feed and fed 4 times a day. The feed ingredients are disinfected or heat-treated.

5. The method according to claim 1, characterized in that, In step S4, the developmental stage determination of the two-stage ion trajectory control includes: determining the Z1-Z5 stage and the Z6 initial stage based on the morphological characteristics of the larvae, and determining that the proportion of juvenile shrimp is not less than 70% as the end condition of the second stage by random sampling and counting.

6. The method according to claim 1, characterized in that, In step S4, the first stage involves adding calcium salts to enrich calcium ions and making the mass concentration ratio of potassium ions to calcium ions lower than that of natural seawater dilution. In the second stage, potassium and magnesium salts are added to increase the ratio of potassium and magnesium ions to calcium ions, thereby reducing the fluctuation of the later metamorphosis survival rate under low salinity conditions.

7. The method according to claim 1, characterized in that, In step S5, the unicellular algae include at least two of Chaetoceros, Brown finger algae, and Chlorella; the microecological preparation includes one or more of photosynthetic bacteria, Bacillus, and lactic acid bacteria.

8. The method according to claim 1, characterized in that, In step S5, when the total ammonia nitrogen is greater than 0.5 mg / L, the nitrite is greater than 0.1 mg / L, or the total number of Vibrio is greater than 1×10² CFU / mL, the treatment capacity of the bypass purification circuit is increased and the siphon discharge is intensified; the daily treatment capacity of the bypass purification circuit is 0.5 to 2.0 times the volume of the seedling pond water, and is increased to 1.5 to 3.0 times when any condition is triggered.

9. The method according to claim 1, characterized in that, The method also includes step S6, in which the tailwater is treated by solid residue removal, activated carbon adsorption, nano-filter ball filtration and reverse osmosis desalination, and the product water is reused for water distribution or makeup water. The concentrated brine is treated by selective softening flocculation and brine classification to obtain ion mother liquor, which is used for ion replenishment in stage Z6. The solid residue removal includes multi-stage screening and filtration, with the final filtration pore size not exceeding 120 mesh; the desalination rate of the reverse osmosis desalination is not less than 95%, and the resulting permeate is reused for the source water replenishment in step S1; The selective softening flocculation involves adding an alkaline softening agent to concentrated brine to preferentially precipitate calcium ions and separate the solid phase, thereby obtaining softened brine; then, the brine is graded according to conductivity and the concentrations of potassium, calcium, and magnesium ions to obtain an ion mother liquor that meets the requirements for ion trajectory control in the Z6 stage.

10. The method according to claim 9, characterized in that, In step S6, the resulting produced water is reused for the source water replenishment in step S1 and the brine preparation water in step S2.

11. An artificial seawater assembly for implementing the method according to any one of claims 1 to 10, characterized in that, Includes basic pre-prepared salt, first-stage ion compensation pack, and second-stage ion compensation pack; The basic pre-prepared salt is used to prepare freshwater to a salinity of 6.0–10.0‰; the first-stage ion compensation package is used to ensure that the seedling water in stages Z1–Z5 meets the following requirements: calcium ion concentration of 180–260 mg / L, potassium ion to calcium ion mass concentration ratio of 0.55–0.85, and magnesium ion to calcium ion mass concentration ratio of 1.0–1.6; the second-stage ion compensation package is used to ensure that the seedling water from stage Z6 to stage Z5, when the proportion of juvenile shrimp is not less than 70%, meets the following requirements: calcium ion concentration of 110–150 mg / L, potassium ion to calcium ion mass concentration ratio of 1.25–1.70, and magnesium ion to calcium ion mass concentration ratio of 2.0–3.

0.

12. The artificial seawater assembly according to claim 11, characterized in that, The basic pre-prepared salt includes sodium chloride, magnesium salt, calcium salt, potassium salt, bicarbonate and trace element salt, wherein the trace element salt includes one or more of borate, strontium salt and bromide salt; the second-stage ion compensation package and the ion mother liquor obtained in step S6 of the method of claim 9 can be mutually substituted as the source of potassium and magnesium ions in the second stage at a mass fraction of 10% to 80%.

13. A breeding system for giant freshwater prawns, used to implement the method described in any one of claims 1 to 10, characterized in that, It includes a source water pretreatment unit, a salt preparation unit, a seedling pond unit, an algae and bacteria addition unit, a bypass purification circuit, a tailwater reverse osmosis desalination unit, and a concentrated brine softening and grading and ion mother liquor unit. The source water pretreatment unit is connected to the salt preparation unit, the salt preparation unit is connected to the seedling pond unit, the algae and bacteria addition unit and the bypass purification circuit are respectively connected to the seedling pond unit, the tailwater outlet of the seedling pond unit is connected to the tailwater reverse osmosis desalination unit, the product water outlet of the tailwater reverse osmosis desalination unit is connected to the salt preparation unit, the concentrated brine outlet of the tailwater reverse osmosis desalination unit is connected to the concentrated brine softening and grading and ion mother liquor unit, and the concentrated brine softening and grading and ion mother liquor unit is connected to the seedling pond unit to provide the seedling pond with a second-stage ion supply.

14. The system according to claim 13, characterized in that, The product water outlet of the tailwater reverse osmosis desalination unit is connected to the salt preparation unit and the source water pretreatment unit.

15. The system according to claim 13, characterized in that, The raw water pretreatment unit includes a raw water regulating tank, a solid-liquid separation device, an oxidation disinfection device, and a disinfection residue removal device; the salt preparation unit includes a salt dissolving tank, a stirring or circulation device, a salinity detection device, a pH detection device, and an alkalinity adjustment device.

16. The system according to claim 13, characterized in that, The system also includes a detection module and a control module. The detection module is used to detect the salinity, pH, dissolved oxygen, total ammonia nitrogen, nitrite, total number of Vibrio, and concentrations of potassium, calcium, and magnesium ions in the seedling water. The control module controls the bypass purification circuit treatment capacity, algae and bacteria dosage, water exchange volume, and ion mother liquor dosage based on the detection results.

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